AN INTRODUCTION TO CHEMISTRY Science 2009 2010 Academic Decathlon

In this section, we will cover:Chemistry prior to the Scientific RevolutionAntoine Lavoisier and the Birth of Modern ChemistryChemistry After LavoisierTen Independent Research Topics, including Mixing Metals and RadioactivityA Brief History of Chemistry

Chemistry Prior to the Scientific RevolutionGold copper tin and bronzeIron:Meteorites?Mixed with carbon to form steelGlass and pottery: decoration, utility

IRT: Mixing Metals to Make BronzeBronze: 90% copper, also arsenic, tin, antimony, leadFirst used by Sumerians (3600 BCE)Used for weapons, decorationMethods: open casting, lost-waxSuperior Chinese alloys effective defense

IRT: The Use of Dyes and PreservativesCave paintings and Egyptian tombs Roman Empire, Phoenicians, Minoan CreteWoad, indigo, oxides of mercury, Tyrian purpleMummy wrappings, stained glass, linen and hemp

IRT: Alchemy and the Philosophers StoneTransmutations: base metals into goldPracticed as a science from 331 BCE to roughly 300 CEPhilosophers Stone:TransmutationsElixir of Life

IRT: Gunpowder and FireworksSaltpeter, charcoal, sulfurInvented by Chinese before 1100 CERoger Bacon recipe: Opus TertiumSent to PopeRockets, projectiles cannonsBattle of Crecy: 1346 CE

IRT: Early Thinkers on the Nature of MatterAristotle:Ideas from Plato (used term element) et alFour properties: hot, cold, wet, dryFour elements: fire, air, water, earthFifth element: etherDemocritus:Small discrete particlesProperties of these atoms?

Antoine Lavoisier and the Birth of Modern ChemistryNotable chemists 16th-early 19th century:Johann Baptista van Helmont, Robert Boyle, Joseph Black, Henry Cavendish, Joseph PriestlyAntoine Lavoisier: coherent gathering of current theories (nature of air, oxidation, water, matter)Involved in French Revolution, targeted by Jacobins

IRT: The Living Tree ExperimentJohann Baptista van HelmontLiving systemsTree growing out of water onely [sic]Tree weight vs. soil weight

IRT: Antoine Lavoisier and His Role and Fate in the French RevolutionBorn to a wealthy lawyer, studied accounting and lawPresident of a bank, member of the Ferme Generale (private tax collection agency)Supported the new regime during/after revolutionTargeted and executed links to chemistry and old regime

IRT: Madame LavoisierMarie Anne Pierrette Paulz married Antoine Lavoisier in 1771Father was in the Ferme GeneraleLearned chemistry and English to assist in labArrested and held for 65 days by Jacobins in powerRemarried in 1805, then divorced, died alone

Chemistry After LavoisierHenri Becquerel: radioactivityPierre and Marie Curie: radioactive decayJ.J. Thompson: electronErnest Rutherford: atomic nucleusJames Chadwick: neutronNiels Bohr: electron orbitalsFrederick Soddy: isotopes

IRT: Radioactivity and Nuclear StructureHenri Becquerel: radioactive decay with photographic plates, 1896Pierre and Marie Curie: radioactivity and two new elements (polonium, radium), 1898Ernest Rutherford: alpha particles and atomic structure, 1920James Chadwick: neutron, 1932

Chemistry After LavoisierAlbert Einstein: photoelectric effectLouis de Broglie and Erwin Shroedinger: quantum energy relationshipsPeriodic TableInter-/Intramolecular ForcesDipolesHeat, Work, TemperatureReactants, Products, Chemical Kinetics

IRT: The Periodic Table and Associated PeriodicityDmitri MendeleevRepeating properties among elementsIssues with ordering by weightRe-measuring and skipping positions helpedHenry Moseley: ordering by atomic numbers

Wrap-UpBoth times of peace and war brought about advancements in chemistryAntoine Lavoisier and those like him were vital to the development of modern chemistryChemistry since Lavoisier has developed rapidly across many fields

In this section, we will cover:Atomic Theory and StructureChemical Bonding and Intermolecular ForcesMolecular ModelsNuclear ChemistryTen Independent Research Topics, including Electronegativity and Fission and Fusion ReactionsThe Structure of Matter

Atomic Theory and Atomic StructureAtomic structure dictates element chemical behaviorPositive, negative, neutral particlesWeight of one atom determined by weighing many atomsMass spectrometers: accuracy

IRT: Mass SpectrometrySeparates and measures compoundsMain components:Ion sourceMass analyzerDetectorCurved magnet or cycling magnetic field

Atomic Theory and Atomic Structure: Mass and IsotopesAtomic number: protonsAtomic mass: protons + neutronsSame element with different numbers of neutrons: isotopesCarbon: atomic standard (12 amu)Weighted averages:(isotope A abundance x isotope A weight) + (isotope B abundance x isotope B weight)

IRT: Properties and Importance of Commonly Recognized Isotopes21H (Deuterium):Tracer isotopeFusion reaction with tritium146C:Radiocarbon datingClimate change studies6027Co:Highly radioactive: kills cancer cells and bacteriaExamines steel components

Atomic Theory and Atomic Structure: ElectronsAbsorption or emission spectrum: determining structure of an atomBohr Model of the atom: fixed orbitsQuantum Mechanical Model: non-fixed orbitsElectron clouds: orbits (s and p)Orbital shapes determine bonding behaviors

IRT: Wave and Particle Nature of the Electron and PhotonAll matter exhibits both wave and particle propertiesLight as a particle: photoelectric effectElectrons as energy: Davisson-Germer experiment

Atomic Theory and Atomic Structure:The Periodic TableNumber of orbits determine periodAcross a row (period):Atomic radius decreasesIonization energy increasesElectron affinity increases

Atomic Theory and Atomic Structure: The Periodic TableDown a column (group or family):Atomic radius increasesIonization energy decreasesElectron affinity decreases

IRT: ElectronegativityOne atoms net attraction of electrons from the adjacent atom to which it is chemically bondedHigher value = greater attractionIncreases up a group and across a periodFluorine most strongly electronegativeValues predict winners

Chemical Bonding and Intermolecular Forces: Intramolecular ForcesIonic:Electron transferNaClCovalent:Sharing electronsCH4Metallic:Electron seaBrass

Chemical Bonding and Intermolecular Forces: Intermolecular ForcesVan der Waals force: uneven distribution of positive and negative charges (temporary or permanent)Hydrogen bonds: strongly electronegative atom bonded to hydrogen on another molecule

IRT: The Importance of Hydrogen Bonding in Living SystemsDNA contains hydrogen, oxygen and nitrogenHydrogen bonds in DNA create its double helix structure

Chemical Bonding and Intermolecular Forces: Effects and Properties of BondsSolid structures:Ionic latticeCovalent network or molecular solidTranslational motionStrength of force determines state at room temperatureUneven bonds are polar

Molecular Models: Lewis StructuresG.N Lewis (1875-1946)Lewis StructuresDots represent electronsValence electrons (bonding)Bonding pairs and non-bonding (lone) pairs

Valence Bonds and HybridizationSingle bondOne overlap between orbitalsDouble-bond or triple-bondMultiple overlapsHybridizationDifferent orbital shapes combine to form a new shape

IRT: The Formation of Molecular OrbitalsOrbitals are electron waves in particular positions and shapesSigma (s) orbitalsOverlap concentrated along an imaginary connecting line between nucleiPi (p) orbitalsOverlap concentrated away from connecting line between nuclei

IRT: The Formation of Molecular OrbitalsN2: one sigma and two pi bondsO2: one sigma and one pi bondF2: one sigma bondCO2: one sigma and one pi bond for each oxygen atom

Molecular Models: VSEPR ModelsValence Shell Electron Pair Repulsion modelThree dimensionsMolecular geometry (tetrahedron, linear, et al)

IRT: The Resonance Concept ModelExplains bond properties in mathematically uneven bondsSharing, delocalizing and distributing electrons to satisfy the octetO3 and SO3

Molecular Models: Oxidation StatesAssigned based on electron loss/gainH2O: H = +1 O = -2Sum of oxidation numbers in neutral molecule equals zeroSum of oxidation numbers in charged molecule equals total charge

Molecular Models: Dipole Moments and PolarityDipole momentLack of symmetryBond dipoles do not cancel each other outPolar moleculesHigh polarity strong van der Waals forcesStronger bondsHigher boiling and melting points

Nuclear ChemistryRadioactive atomsUnstable nuclei (varying ratios of neutrons to protons)Regain stability through various pathwaysAlpha decay: loss of helium nucleusBeta decay: neutron protonPositron decay: proton neutron

IRT: Decay Equations and Predicting Products of Decay AlphaAlpha decayVery large nucleiAtoms of bismuth and those largerSample:23892U 23490Th + 42He2+

IRT: Decay Equations and Predicting Products of Decay Beta and PositronBeta (beta-minus) decay:Too many neutronsSample:32H 31He + electron + antineutrinoPositron (beta-plus) decay:Too many protonsSample:104C 105B + positron + neutrino

IRT: Alpha Bombardment ReactionsErnest Rutherford: 1919Nuclear transformations can be caused by bombardment (including alpha bombardment)Example:42He + 147N 178O + 11H

IRT: Fission and Fusion ReactionsExample fission of uranium-235:23592U143 + neutron 13454Xe80 + 10038Sr62 + neutron + neutronProducts vary (typically amu of 130 and 100 plus 2-3 neutrons)Hydrogen-2 and Hydrogen-3 fusion:21H1 + 31H1 42He2 + neutronNot yet feasible for large-scale power

Wrap-UpVarious notations and models are used to express and explain atomic structure and bondsBonds vary in composition, type, structure and polarityLewis and VSEPR models help visually express molecular orientation and geometryNuclear chemistry involves radioactivity and decay reactions of various types

In this section, we will cover:Gases, Liquids and SolidsPhase DiagramsSolutionsFour Independent Research Topics, including Carbon Dioxide and Raoults Law

States of Matter

Gases: Laws of Ideal GasesBoyles Law: P x V = a constant (C)Charles Law: V/T = a constant (D)Combination: PV/T = CDTracking changes:(P1V1)/T1 = (P2V2)/T2

IRT: Partial Pressures and Correction of Gas Volumes Collected Over WaterGas proportions in mixtures expressed in mole fractionsDaltons Law:Mole fraction A = Pressure of A / Total PressureGas container over waterWater vapor pressure relies only on temperatureTotal pressure water vapor pressure = gas pressure

Gases: Kinetic Molecular TheoryFour major assumptions about ideal gases:1. A pure gas consists of tiny, identical molecules2. The molecules move very rapidly in all directions but at different speeds3. No forces of repulsion or attraction exist between the molecules4. Gas pressure is a result of collisions of the molecules with the walls of the container (no loss of energy)

Gases: Particle SpeedAverage molecule speed (u) determines frequency of collisions with given side length (l)Momentum change from collisions determines forceMolecule mass = mForce = (mu2)/lNumber of molecules = NPressure = (1/3)((Nmu2)/V) or PV = (1/3)Nmu2

Gases: Avogadros LawNumber of molecules determines gas behaviorMass less importantGiven temperature, pressure and volume same number of molecules

Gases: Volume and Mass of One MoleOne mole:Number of molecules in a volume of 22.4 liters at 1 atmosphere pressure at 273 KORNumber of atoms in 12 grams of carbon-12Avogadros number: 6.022 x 1023 moleculesMolar mass is g/mol

Gases: Root Mean Square SpeedAverage single molecules speed:u = sqrt((3kT)/m)Root mean square speed of one mole:u = sqrt((3RT)/M)R is the Boltzmann constant recomputed for one mole of gas (universal molar gas constant)

IRT: The Behavior of Gases Under Extreme ConditionsHigh pressure, low volume and low temperature gases do not behave ideallyVan der Waals formula to predict non-ideal gas properties:P = ((nRT)/(V-nb)) ((n2a)/V2) a and b: correction values for volume and molecular attraction (smaller more ideal)Large van der Waals values make for ideal refrigerator coolants

Gases: The Ideal Gas EquationFor one mole: pressure x volume = R (universal molar gas constant) x temperature (in Kelvin)For n number of moles:

Related to the combination of Boyles and Charles Laws

Gases: Relative Rates of Diffusion and EffusionDiffusion: gas spreading out from a sourceEffusion: gas escaping from a small holeImpossible to determine in non-vacuum environmentRelative speeds can be determinedHeavier (more massive) molecules move slower

LiquidsIntermediate between gas and solid:Some intermolecular forces, translational motionModerate degree of order

LiquidsLong-range ordering (depends on qualities of liquid)Water is more ordered than other liquids like octane (stronger forces)Intermediate density (between gas and solid)

SolidsSolids are highly orderedTypes:Ionic latticeCovalent networkMolecularMetallicSome substances exist in multiple forms (allotropes)

SolidsCarbon: many different bonding arrangementsGraphite: stable at room temperatureDiamond: formed when graphite is under high pressureCan be created in labsParticle size affects structureClosely-packed particles have strong bonds

Solids: Properties of MetalsSimple metallic structures:Body-centered cubic (shown)Cubic closest packedHexagonal closest packingProperties of metals:LustrousGood conductors of heat and electricitySonorousMalleableDuctile

Phase Diagrams: Concepts1. Constructed assuming a sealed container2. Dynamic transfer3. Equilibrium4. Vapor (gas) present at any temperature

Phase Diagrams: Features

Phase Diagrams: WaterBackward-sloping line between solid and liquid statesGives ice and liquid water unique properties

IRT: Carbon DioxideLiquid CO2: difficult to observeHigh pressure and low temperatureSupercritical CO2: industrial solvent

Solutions: ConceptsSolubility: how much of a solute will dissolveConcentration: relative amounts of solute in a solutionPhysical properties: some occur when solutions are formed

Solutions: Types and FactorsLike dissolves like:Water (polar) with salt or sugarOctane (non-polar) with vegetable oilStrong reaction with water: hydrationSolubility : the relationship between intermolecular forces and forces trying to break molecules apart

Solutions: Solubility RulesCommon compounds of group I and ammonium are solubleNitrates, acetates and chlorates are solubleBinary halogens (not F) are soluble with metals, except Ag, Hg(I) and PbSulfates are soluble, except barium, strontium, calcium, lead, silver and mercuryExcept for the first rule, carbonates, hydroxides, oxides, silicates and phosphates are insolubleMost sulfides are insoluble except calcium, barium, strontium, magnesium, sodium, potassium and ammonium

Solutions: Aqueous SolutionsMaximum dissolved solute: saturated solutionLowering temperature can bring crystals out of solutionIons combining in solution to form insoluble particles precipitatesStalactites and stalagmitesCompounds with O-H bonds dissolve in water (glucose)

Solutions: Organic SolventsOften contain only carbon and hydrogenUsed for grease and oil removalToxic to humansDisposed by burningRecent developments modern soap and detergent: interact with non-polar molecules but are water-solubleSupercritical fluids: solvents?

Solutions: Expressing ConcentrationPercent CompositionX grams of a solute in Y grams of solvent (usually 100)MolarityMoles of solute per liter of solutionUsed in scientific applicationsMolalityMoles of solute per kilogram of solventMole fractionTracks colligative properties

IRT: Raoults Law and Colligative Properties: SaltsPhysical properties of a solution are relative to number of moles of soluteSalts in water create larger than expected changesNaCl in water has twice the effect: two moles of ions per mole of NaClCaCl2: three moles of ions per mole of CaCl2Salts lower freezing point of water deicing roadsNaCl is harmful to the environment so calcium magnesium acetate has been proposed (et al)

IRT: Raoults Law and Colligative Properties: Distillation of WaterVapor above a solution is pure solventDistillation seeks to capture this vapor (in a water-based solution) to collect drinking waterEasier to scale up, less setup and maintenance, less wasteReverse osmosis is the most viable alternativeWater is pressurized and pumped through membranes that filter out impuritiesLower energy needs, lower discharge water temperature, purer output, smaller physical area

Wrap-UpGases, liquids and solids each have unique properties that govern their behaviorPhase diagrams illustrate the transitions between and conditions of these three statesThese behaviors and conditions are important in determining how substances will interact and what the products of those interactions (solutions) will be

In this section, we will cover:Acid-Base, Precipitation and Redox ReactionsElectrochemistryStoichiometryEquilibriumKineticsThermodynamicsFive Independent Research Topics, including Electroplating and Hess Law

Reactions

Types of ReactionsSynthesis (combination)A + B C or 2Na + Cl2 2NaClDecompositionA B + C or 2H2O2 2H2O + O2Double replacementAB + CD AD + CB or Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)

Types of ReactionsSingle replacementWith metal: M + BC MC + B Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)With non-metal: N + BC BN + C Cl2 + 2KBr 2KCl + Br2

Types of ReactionsCombustionReactant + O2CH4 + 2O2 2H2O + CO2Produces heat and sometimes lightProperties of substances involved dictate the type of reaction that will occur

Acid-Base Reactions: TheoriesArrheniusAcids yield H+Bases yield OH-NH3: basic but with no OH-Brnsted-LowryAcids donate H+Bases receive H+Explains NH3 (it receives H+)Water can be an acid or base: amphoteric

Acid-Base Reactions: pHpH = -log[H3O+]0-14 scaleBelow 7 is acidic, above 7 is basicExactly seven is neutral (like pure water)All acidic and basic solutions have both acids and bases in them

Acid-Base Reactions: TitrationsTitration: acids and bases mixed together and measured as they interactEndpoint or equivalence point: moles of acid and base are equalColored indictor shows this point

Acid-Base ReactionsAcids can be diprotic or triproticDouble replacement reaction:acid + base salt + waterSalt product can be acidic, basic or neutralStronger acids transfer more hydrogen ions to water

IRT: Acid-Base Reactions and SaltsSalt ions can interact with water: hydrolysisCan produce basic, acidic or neutral solutionsBasic salt (sodium acetate) in waterWeak acetic acid in a basic solutionAcidic salt (ammonium chloride) in water Ammonia (weak base) in an acidic solutionNeutral salt (sodium chloride) in waterNo reaction, neutral solution

Precipitation ReactionsA type of double replacement reactionTwo solutions mixed one of the products comes out of solution as a solidSpectator ions: ions not forming precipitates

Precipitation Reactions: ExampleBalanced reaction equation:AgNo3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)With ions separated:Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) AgCl(s) + NO3-(aq) + Na+(aq) Net reaction with no spectators:Ag+(aq) + Cl-(aq) AgCl(s)

IRT: PrecipitatesMercuryHarmful to people and the environmentIndustries have reduced outputAtmospheric particulatesHarmful inside the lungsCan be brought out of solution as precipitateSilverUsed in solution to develop photographsCan be reclaimed and used for other purposes

Oxidation-Reduction ReactionsOxidation: loss of electronsReduction: addition of electronsOxidation numberEqual to the number of electrons that must be added or subtracted to make an element neutralCan be positive, negative or neutral

Oxidation-Reduction ReactionsRules of oxidation states:Group I elements are all +1Oxygen is -2Neutral atoms are 0, neutral compounds add up to 0Polyatomic ions must add up to the total chargeElectrons are conservedAll freed electrons must be usedBalanced equation example:Cu + 2Ag+ Cu2+ + 2Ag

Electrochemistry: TermsElectrochemistry uses redox reactionsElectroplating (including chromeplating)Voltage: tendency of electrons to leave or join an atom (cell potential)

Electrochemistry: VoltageVoltage = potential of oxidation potential of reductionPositive values proceed forwardNegative values proceed in reverseCu + 2Ag+ Cu2+ + 2AgCu Cu2+ + 2e- E = -0.34 VAg+ + 1e- Ag E = +0.80 V(-0.34 + 0.80) = +0.46 VSpontaneous reaction

Electrochemistry: Galvanic Electrochemical Cell & ElectrolysisJ. F. Daniell 1836Earliest reliable batteryAnode: oxidationCathode: reductionElectrolysis: nonspontaneous reaction with voltage applied

IRT: ElectroplatingAuto industryChrome plating: hardness, corrosion-/wear-resistanceAerospace industryGold plating: non-reactive protection, reflectivityPlatinum, palladium, nickel, copper, silver and rhodiumFaraday: electric charge on one mole of electronsOne Faraday = 96,500 coulombs of chargeVoltage used x coulombs needed = energy in kilojoules

IRT: The Nernst EquationConnects cell potentials to free energy changes in chemical reactionsE = E RT ln Q/nF or E = E (0.0592 log Q)/nExample:Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)+1.10 under standard conditions, n for Zinc is 2E = +1.10 0.0592/2 log [Zn2+]/[Cu2+]Equal concentrations of reactants and products yields standard value (+1.10)

StoichiometryBalanced equations that keep track of substancesStoichiometry preserves ratios of substancesSame principle used in cooking and recipe conversionApplies to ion charges and redox reactions

StoichiometryStoichiometry is used to determine yieldsLimiting reactant: the substance in a reaction that will determine how much one can yieldExample: 2H2 + O2 2H2O with 12g of H2 and 32g of O212g/2 M = 6 moles of hydrogen32g/32 M = 1 mole of oxygen4 moles of hydrogen left overOxygen is the limiting reactant

EquilibriumReactions do not always go in just one directionForward and reverse at same rate: equilibriumEquilibrium constant: K = ([C][D])/([A][B])Ka Acids, Kb Bases, Ksp Precipitates, Kp Pressures of gases, Kc Solutions and concentrationsIf K > 1, there is more product in the endIf K < 1, there is more reactant

EquilibriumConversion from Kc to Kp value:Kp = Kc(RT)nSmaller values of Ka and Kb mean weaker acids and basesKsp indicates how much solid will ionize and solubility of insoluble substancesSmall Ksp values indicate a precipitate will form

KineticsKinetics: how fast reactions happen and what affects that rateRate law: algebraic equation determined by concentrations and their effect on reaction ratesRate is determined by change in concentration over timeInstantaneous rate can be determined on a graph

KineticsCollision model: conditions affect rate of collisions (i.e. rate of reaction)Increasing temperature increases rateHigher concentration increases rateActivation energy: energy needed to activate the reaction

KineticsCatalysts lower the required activation energyCatalyzed reactions require less energy and are fasterRates of chemical reactions in the human body use catalysts called enzymes

Thermodynamics: ConceptsThermochemistry measures energy changes in chemical reactionsThermodynamics: energy and temperature are related to particle motionSystem + surroundings = universeState functions: volume, energy content and pressure

Thermodynamics: Heat and ReactionsExothermic reactions give off heatEndothermic reactions absorb heat

Thermodynamics: First LawEnthalpy: the energy content given off or taken in by a chemical reaction (symbol H)Enthalpy is a state functionDirectly proportional to the moles of a chemical presentHeat of formation: enthalpy change during formation of a compoundMeasured by calorimetry

IRT: Hess LawGermain Hess (1802-1850)Heat energy in a chemical reaction is the same no matter the number of stepsUnknown enthalpy values can be calculated using other known enthalpy valuesIf H is known for the formation of CO2, and for the oxidation of CO to CO2, then H for the formation of CO can be calculated

Thermodynamics: Second LawEntropy: energy associated with disorderState function (symbol S)Smaller values indicate greater orderWhether or not a chemical reaction will occur relies on both enthalpy and entropyGibbs Free Energy (state function, symbol G)G = H TS (T is temperature in Kelvin)Signs of terms determine spontaneity of reactions

Relationship of Change in Free Energy to Equilibrium Constants and Electrode PotentialsFree energy to equilibrium constants:G = -RTlnKFree energy to cell potential:G = -nFEcell

GKEcellReaction under standard-state conditionsNegative>1PositiveFavors products010EquilibriumPositive

Wrap-UpThere are several categories of reactions, all of which have different sub-categories (acid-base, precipitation, redox)Studies of electrochemistry (et al) have led to industrial advancesStoichiometry is invaluable to scientific workAn understanding of equilibrium, kinetics and thermodynamic is vital to understanding how and why reactions proceed as they do

**Although scientists are not 100% certain, the first metal used was probably gold. The earliest ornaments made of gold have been dated all the way back to the Neolithic Age. Copper might have been the next metal utilized by humans, including those in Egypt and Mesopotamia. Tin and an alloy known as bronze (tin and copper together) were likely next, and were used both for decoration and weaponry. Zinc and brass (a zinc-copper alloy) were in use before the Roman Empire came to power. The first iron used by humans probably came from meteorites. Iron, an element occurring relatively rarely in nature, was mixed with carbon to make steel (first done circa 1700 BCE). Because steel is ideal for weapons manufacturing, it had a significant impact on political shifts and conflicts. Glass and pottery have been used for thousands of years, created by hearing sand or clay. Archaeological evidence suggests that glass and pottery were widely traded and were used for both decorative and utilitarian purposes.*Bronze can be made from a variety of metals, but generally the alloy is 90% copper and 10% everything else. When the Sumerians made the first bronzes around 3600 BCE, they used arsenic with copper, and later added tin. Some bronzes found also contain antimony and lead. Bronze is useful for weapon-making because its ingredients are easily melted and can be poured into casts to create the desired shape. The finished product is stronger and more durable than the individual parts would have been. The open casting method involved pouring the liquid bronze into a stone mold, then hammering the cooled object into its final shape. In the lost-wax method, a wax model would be made of the desired shape, then a mold of pottery clay would be formed around it. When firing the pottery, the wax would melt away, leaving a pottery mold of the exact shape for casting. In China, metallurgists experimented with different metals (including titanium, magnesium and cobalt) to create even stronger and more durable alternative versions of bronze. These techniques undoubtedly contributed to the Qin Dynastys ability to fend off invaders.*Beginning tens of thousands of years ago, humans used dyes to add color to cave paintings. Following that, dyes were used for clothing, mummy wrappings in Egypt, stained glass in Europe and other linens. Both woad and indigo create blue colors, oxides of mercury can make yellows and reds and sea snail shells (pictured) off the coast of Tyre create a rich purple color known as royal purple or Tyrian purple. Because this purple was so expensive to make, its use was considered a sign of wealth. Mummy wrappings were dyed with yellow and red oxides of mercury that also acted as preservatives. Beginning with Egyptian Pharaohs and continuing into the Middle Ages, dyes were added to molten glass to create beautiful stained glass (commonly seen in churches all over Europe).*The main concept behind alchemy is that, though some mysterious process, base metals could be turned into gold. This change is known as a transmutation. For hundreds of years (typically believed to have started in 331 BCE in Alexandria and losing favor as a real science by 300 CE), alchemists tried to determine by what procedure these transmutations could be achieved. Of course, there was no success, though some reported it in order to get more funding for their research. In the lore of alchemy, the most widely known artifact was the Philosophers Stone. According to legend, it could not only cause transmutations to occur, but it could also create a substance known as the elixir of life. This elixir could give youth and extend life, which purportedly worked for Nicholas Flamel, who likely lived from 1330 to 1417. [Basically, the plot of the first Harry Potter story. Amber]*Gunpowder is made up of saltpeter, charcoal and sulfur. It is believed that the Chinese invented gunpowder (they called it artificial fire) sometime before 1100CE and had begun using it not only for fireworks but also mainly for weapons such as rockets and projectile weapons (shown in a battle above). In 1268 CE, Roger Bacon sent a recipe for gunpowder to the Pope. It was included in his book Opus Tertium, which translates to third work. By the time this recipe arrived in Europe, the Chinese had large gunpowder factories in which they were making 7,000 rockets and 21,000 bombs per day. Cannons became a mainstay of battle in both Europe and Arabia, with both sides realizing the value of having gunpowder on their side. In the Battle of Crecy in 1346 CE, the English army made some use of gunpowder, though not to the extent that it would later be used in militaries across the globe.*Aristotle (384-322 CE) took ideas from Euclid (geometry) and Plato (the concept of the element) to create his own theories on the nature of matter. He believed that each element had a three-dimensional structure and that the combination of all these structures is what created the matter we see in the world. Aristotle categorized matter into four categories (fire, air, water, earth) based on four basic properties (hot, cold, wet, dry). A fifth element, described as an immaterial ether, was thought to exist in addition to these simple categories. Aristotles elements remained the basis of chemistry and concepts of matter for many centuries after his death. Democritus (also called Demokritus or Abdera, 460-370 CE, pictured) believed that all matter was made up of small, hard particles that were too small to be seen with the naked eye. He called them a-toma, or indivisibles. He pondered he properties of these atoms, attempting to determine if they differed from one another in smell, taste, or color.*Beginning sometime around the 16th century, scientists began making key observations about the nature of matter and how matter interacts. Eventually, matter was categorized into three groups (solid, liquid, gas). Johann Baptista van Helmont, a Belgian noble, developed an accurate balance, coined the term gas, identified and demonstrated the law of conservation of mass and scientifically refuted alchemy. His work was supported and continued by a large group of French and British scientists, including Robert Boyle, Joseph Black, Henry Cavendish, Joseph Priestly and Antoine Lavoisier. Lavoisier (1743-1794) pulled together the work of many of these and other scientists to try to create coherent rules for chemistry. He discovered that air is made up of oxygen and nitrogen, that oxidation (a point of fascination for many scientists at this time) is a reaction with oxygen, that water cannot change into earth and that matter is always truly conserved in reactions. He also tried to create an organized system for naming chemical compounds. Unfortunately, just as France was at its peak of scientific learning (mainly chemistry and mathematics), political instability and revolution threatened to undo all the progress that had been made. The revolutionaries (Jacobins) saw scientists as an outdated aristocratic appendage and they later abolished the Academy of Sciences in France. Lavoisier, widely known as a chemist and a government employee, was also targeted.*Johann Baptista van Helmont (pictured) performed an experiment to ascertain the nature of living system, specifically that of a tree growing in soil. He took measurements of weight at the beginning of the experiment, noting that the tree was five pounds and the soil was 200 pounds. At the end of the experiment, after van Helmont had added only water for five years, the tree weighed 169 pounds and the soil was just under 200 pounds. Van Helmont came to the conclusion that the tree had gained 164 pounds from only the water that was added, because there was just as much soil after five years as there had been at the beginning of the experiment. Of course, van Helmont did not know of the concept of photosynthesis, which explains that plants get a great deal of energy from sunlight, and hence can convert that energy into matter. Despite this modern problem with the conclusion of the experiment, scientists then and now were amazed at the attention to detail and specific documentation that van Helmont utilized in his experiment. The living tree experiment still serves as a model of true scientific thinking and procedure.*Antoine Lavoisier brought the mind of an accountant into his scientific studies. He worked for several private groups but often helped the monarchy. As director of la Caisse dEscompte, or Discount Bank, he funded the governments projects and international aid efforts (including the war for independence in America). He sympathized with the lower classes, however, and often sought to soften tax penalties and more fairly distribute the wealth among all citizens. His political straddling of this line made him both very powerful friends and very powerful enemies. During and after the revolution, many institutions to which Lavoisier belonged were abolished, including the Academy of Sciences and the Ferme Generale. Although Lavoisier worked for the new government and supported many of their aims, the regime sought out and captured former employees of the Ferme Generale and executed 28 of them, including Lavoisier. He was guillotined in public on May 8, 1794.*Marie Anne Pierrette Paulz (1758-1836) married Antoine Lavoisier when she was only thirteen years old, but even at that young age she was quick to take up the study of chemistry. She assisted her husband in many of his experiments and even learned English so that she could translate scientific papers for him. After her husband and father, both of whom worked for the Ferme Generale, were arrested and executed by the revolutionaries during the Reign of Terror, Madame Lavoisier was also arrested and held in jail for 65 days. After her released, she had many suitors but waited until the age of 47 to remarry (to Benjamin Thomas, Count Rumford). The union lasted only four years, and she lived alone thereafter until her death at 78.*Despite the setbacks in France following the revolution, chemistry across the West flourished and developed at a rapid rate. Studies of radioactivity and radioactive decay helped explain nuclear/atomic structure, which was mapped out by the discoveries of the electron, nucleus, and neutron. The further refinement of the concept of electrons by Niels Bohr paved the way for understanding how molecules connect to one another. In addition, the discovery of isotopes made possible much later advancements such as carbon-dating and nuclear power.*Henri Becquerel was the first scientist to identify radioactive decay. He placed uranium near unexposed photographic plates; when developed, the plates were developed, they showed images of the minerals produced by radioactive decay. The Curies discovered two new elements after chemically separating them out from a huge sample of uranium ore. Only a few milligrams of polonium and radium were found in the two tons of uranium, but it was enough to study and categorize the new elements. Rutherford and his students bombarded gold foil with radioactive alpha particles. A few of these particles bounced off of the foil instead of passing straight through, which led Rutherford to conclude that only a large, highly-charged central nucleus would cause this reaction. Rutherford determined that the atoms must have a large, positively-charged nucleus with smaller, negatively-charged electrons surrounding the nucleus. He stated that there must be enough negatively-charged particles to balance the strong positive charge of the nucleus. James Chadwick repeated experiments done by Marie Curies daughter in which the younger Curie had bombarded beryllium foil with alpha particles, which gave off a neutral radiation. Curie characterized this as gamma radiation. In Chadwicks experiment, he determined that the neutral particles produced in the experiment must be large enough to knock hydrogen atoms out of parrafin wax. With this interpretation, he characterized the neutron.*Well into the twentieth century, developments and discoveries expanded the known chemical universe. More and more complex concepts, such as those considered by Einstein, Broglie and Shroedinger, were built upon knowledge gained only decades or century before. So many elements were being discovered that a comprehensive organizational model was needed to keep them all in order; that model became the periodic table of the elements. With the advance of means by which atoms and molecules can be examined and measured, concepts such as dipoles and molecular bonding were studied at length. Additionally, the relationships between heat, work and temperature were studied and the understanding of these concepts led to a refinement across the board in chemistry. The study of reactions, including reactants and products, led to further developments in understanding reaction rates and barriers to those rates.*In 1869, Mendeleev proposed his first version of the periodic table of the elements. In his studies, Mendeleev noted that many elements shared properties with one another, and that these properties seemed to repeat in patterns (periodicity). When he ordered the elements by atomic mass, these patterns generally lined up. There were, however, some problems; not all elements seemed to fit properly, and several needed to be reversed. Re-measuring helped to solve some of these problems, and others were dealt with by skipping spots on the table. Mendeleev was correct in assuming that these spaces would be filled up by missing elements (like gallium, discovered in 1875). The final major change to the periodic tables ordering system was suggested by Henry Moseley in 1914, who stated that, because ratios of isotopes would throw off the system already in place, the elements should be ordered by atomic number instead of mass.*Developments like gunpowder, bronze and radioactivity show that both war- and peacetime chemistry produce valuable discoveries. When searching for more durable weapons or just for answers to questions about the nature of matter, leaps forward occur as long as society allows them to. After the French Revolution, sciences (except biology) were shunned, but fortunately, other countries across Europe and the rest of the world did not stop experimenting and trying to discover new concepts in chemistry. Antoine Lavoisier, considered the father of modern chemistry, helped begin a revolution of his own in terms of coherent organization of thoughts, connections between disparate studies and an accountants mindset of attention to detail in all his work. Since his time, there have been hundreds of massive advancements in many areas of chemistry, many of which have played key roles in world politics and society.**Atoms are the smallest distinct particles of matter. All matter is made up of atoms. The structure of any given atom dictates how that matter will behave. They are made up of three types of particles: protons (positive), neutrons (neutral) and electrons (negative). It is impossible to weigh one atom, but by weighing many of the same type of atom, the weight of one can be determined mathematically. These calculations are possible because of established relative atomic masses; scientists know how much of a given element will combine with another (for example, one gram of hydrogen will bond with 19 grams of fluorine), and can therefore create a scale of relative masses. Today, mass spectrometers weigh atoms and molecules using a magnet. Mass spectrometers are incredibly accurate and can perform complex measurements and calculations.*Mass spectrometers are used to measure the mass of a given compound, molecule or element. It works by making the compound into positive ions and accelerating them into a magnetic field, where they take different pathways depending on the atoms weights. The heavier masses take a wider path and end up on the outside while the lighter masses take a tighter path and stay on the inside. The detector or collector at the end records how much of each mass is present. In one common type of mass spectrometer, the compound is passed through a curved magnet. Another type, used at airport security stations, uses a straight pathway with a cycling magnetic field.*All atoms contain one or more protons, one or more electrons and (except for Hydrogen) one or more neutrons. The atomic number of an element is determined by the number of protons present in its nucleus. Atomic mass is determined by the number of protons plus the number of neutrons. While the number of protons in an element is the same for every atom of that element, there can be different numbers of neutrons; these variations of an element are known as isotopes. Some isotopes are more stable than others, and isotopes exist in different proportions. Although hydrogen was originally considered the atomic standard (one atom of hydrogen is one mass unit), it was deemed more convenient to call carbon the standard (one atom of carbon is twelve mass units). To determine the weighted average of an element, the isotope weights and abundances (as a ratio or percentage) must be known. For example, the weighted average mass of a chlorine atom would be (.75 x 35) + (.25 x 37), or 35.453.*Deuterium, an isotope of hydrogen with a neutron (common hydrogen has no neutrons), is found in one out of every 6500 hydrogen atoms in water. Because its ratio is known, additional deuterium can be added in experiments as a tracer element to determine what happens to what amount of deuterium in reactions. Deuterium might also become an important component in fusion reactions, because it reacts very powerfully to tritium, or hydrogen with two neutrons. Carbon-14 is an unstable isotope of carbon with a half-life of 5,730 years. It is created when cosmic rays hit nitrogen in the upper atmosphere. Carbon-14 is found in all living things and decays at a known, predictable rate; therefore, it is used to determine the age of biological material that has long since died. Because of its pervasive nature, it is also being used to determine possible effects of global climate change. Cobalt-60, an isotope of cobalt that does not occur in nature, is highly radioactive and has a half-life of only 5.3 years. It is harmful to cells, so it is used to fight tumor cells. It also kills bacteria and sterilizes foods and medical equipment. Because it can penetrate metal better than x-rays, it is used to examine steel components to check for possible flaws in welds.*All atoms have at least one electron orbiting the central nucleus. By heating (exciting) atoms and causing them to absorb and then emit a photon, then measuring the energy of the photon, scientists can determine the energy levels of electrons. Niels Bohr and other scientists used this information to create a model of the atom. In the Bohr Model of the atom, electrons exist in fixed orbits around the nucleus of the atom. Each orbit remains a specific distance from the nucleus. No more than two electrons can exist in the exact same orbit. When scientists began to recognize that matter exhibited wave properties, a new model of the atom was create to take these properties into account. In this Quantum Mechanical Model of the atom, electrons do not rotate at fixed distances or in exact orbits. They occupy an electron cloud known as an orbital. Orbitals have different shapes, including s and p. These shapes determine the chemical bonding properties of an atom.*Classical thinking states that energy and matter have totally different properties, but we now know that this is not true. Light has properties of matter and waves. In the photoelectric effect (as demonstrated by Albert Einstein), light behaves as a particle when it produces an electric current on a metal surface (pictured). Electrons have wave properties as shown in the Davisson-Germer experiment. The two scientists aimed electrons at a nickel plate and discovered that the electrons exhibited diffraction just like light.*All elements in each row or period of the period table share the same number of electron orbitals. These periods also share other characteristics. Across a period from left to right, the atomic radius decreases because, as electrons are added, the attraction between electrons and the positively-charged nucleus draws the electrons closer to the nucleus, making the atoms smaller. The ionization energy, the energy required to remove an electron from an atom, increases from left to right in a period. The electron affinity (the energy change when an atom is made into a negative ion) also increases from left to right. *Down a group in the periodic table, the trends are essentially the reverse of those across periods: the atomic radius increases while the ionization energy and electron affinity from decrease. The greater number of electrons and their distances from the nucleus are responsible for these trends.*Electronegativity is a measure of the attraction of electrons of one atom to the adjacent chemically-bonded atom. The higher the Pauling electronegativity value, the greater the attraction. The highest values on the periodic table are in the upper right, with Fluorine having the highest value (almost 4) and Francium having the lowest non-zero value (.7). When predicting the behavior of electrons in chemical bonding, the relationship between the two electronegativity values of the atoms can determine who will win the electron(s). If the values are very disparate, it is likely that an ionic bond will form with the stronger atom winning. If there is little to no difference, a covalent bond will form.*Intramolecular bonds are very strong and difficult to break. They are categorized as ionic, covalent or metallic. Ionic bonds (shown) exist when one or more electrons transfer from one atom to another and form a bond. The atoms involved become positive and negative ions, respectively. Sodium chloride is an example of an ionic bond. Covalent bonds exist when atoms share electrons between them. Methane, or CH4, is an example of a covalent bond. Metallic bonds exist between atoms of one or more metals (like sodium or lithium). Electrons can move freely between the atoms, creating an electron sea. These bonds allow metals to have their superior conductivity. Alloys like brass exhibit these bonds.*Intermolecular forces, generally weaker than intramolecular forces, exist between molecules. Van der Waals force, named after Johannes van der Waals, exists when there is an uneven distribution of charge between molecules, causing either a permanent dipole or a temporary dipole moment or induced dipole. These forces are known as London dispersion forces. Hydrogen bonds exist when a strongly electromagnetic atom bonds with hydrogen on another molecule. Such a bond exists in water, in which the hydrogen atom on one water molecule forms a weak bond with the strongly electromagnetic oxygen atom on another molecule. These bonds give water unique properties, like its high boiling point and the ability of ice to float on cold liquid water.*DNA is made up of nucleic acids, which contain hydrogen, oxygen and nitrogen atoms. Oxygen and nitrogen are ideal for hydrogen bonding. When hydrogen has a strong dipole-dipole reaction with these atoms, it forms a bond and modifies the structure of the matter. It is this bonding that gives DNA its double helix shape.*Depending on the types of bonds, the solid structures that are formed can fall into several categories. In ionic bonds, the forces extend in all directions beyond the atoms involved, so an ionic lattice is created. NaCl is an ionic lattice. Covalent networks exist when covalent bonds form a lattice with other molecules, such as in the case of diamonds. Molecular solids are formed similarly but are much weaker because they are held together by weaker intermolecular bonds (as in the case of ice and solid carbon dioxide). Translational motion, or molecular movement, does not occur in solids. It occurs to some extent in liquids, and is most extreme in gases. The strength of the bond also indicates the state of the molecules at room temperature. For example, covalently-bonded quartz is a solid. Intermediate strength bonds, like hydrogen bonds, create liquids at room temperature. Very few molecules are naturally liquids at room temperature. The weakest bonds form gases, like carbon dioxide. In all bonds except those between identical atoms, some polarity will exist as electrons are drawn toward the atom with the strongest electronegativity value. Such situations are known as polar bonds.*G.N. Lewis was at the University of California when he developed the idea for an atomic model that helps account for electron placement in compounds. In these Lewis structures, dots (electrons) surround the chemical symbol (nucleus). Though sometimes all electrons are shown in the diagram, often only the valence electrons (those involved in bonding) are shown. In addition to these bonding pairs, Lewis structures show the non-bonding pairs, also known as lone pairs. Lewis structures of this type are only used for covalently-bonded molecules.*In order for both the Lewis structures and orbital theory to apply to bonds, there must be a theory that encompasses both ideas. This theory states that electrons on an orbital on the first atom interact with electrons on an orbital on the second atom. When this interaction occurs between only one orbital on each atom, it is known as a single bond. Each additional orbital involved adds a bond, as in the case of the double bond and triple bond. In hybridization (shown), the two orbitals interact to create a differently-shaped orbital that would not be predicted of a typical bond.*Molecular orbitals dictate the position and shape of electrons in molecules. The original atomic orbitals combine when the molecule is formed and overlap. The properties of the molecule determine the type of orbitals formed. In sigma orbitals, the overlap is concentrated along an imaginary center line between the two atoms. In pi orbitals, the overlap is concentrated between the atoms but away from that center line.*Many molecules form multiple bond shapes at the same time. In the case of N2, one sigma and two pi bonds are formed. One sigma and one pi bond are formed with O2. F2 has only one sigma bond. With CO2, it is slightly more complicated, with one sigma and one pi bond for each of the connections between the oxygen and carbon.*VSEPR (pronounced vesper) models are used to demonstrate the theoretical three-dimensional properties of molecules. Given that electrons are negatively charged and presumably repel each other in three dimensions, each molecule must have a three-dimensional shape based on this electron repulsion. For example, methane (CH4) forms a tetrahedron (pyramid with a triangle base, shown) while CO2 forms a linear structure. There are fifteen general categories of molecular geometry shapes, including triagonal planar, bent and octahedral.*The resonance concept model was devised to help explain the length and strength of bonds that should not have such properties. For example, the molecule O3 (shown as first image) should not have enough valence electrons to have double bonds in each pairing, yet it appears to have the same bond between both. Numerically it should not work, but it does. The resonance concept models states that, in this case, the double bond could be between either of the two pairs at any given time and is, effectively at least, in both places at the same time. The same is true for SO3, in which all three bonds appear the same in experiments, yet there are not enough valence electrons to make this mathematically true.*Oxidation states are numerical values that are assigned based on electrons lost or gained when bonds are formed in a molecule. For example, in H2O, each hydrogen molecule gives an electron to bond with the oxygen molecule, which gives each hydrogen an oxidation number of +1. The oxygen, effectively gaining two electrons in these bonds, has a value of -2. In neutral molecules (no net charge), the sum of all the oxidation numbers must be zero. In charged molecules, the sum of all the oxidation numbers must equal the net charge of the molecule.*A molecule is said to have a dipole moment when the distribution of charge along the molecule is not symmetrical. In this case, the charges do not immediately cancel each other out. This quality will determine the geometry of a molecule. For example, CO2 does not have a dipole moment; therefore it is linear. Polar molecules have a permanent nonsymmetrical distribution of charge on the molecule. High polarity means that there will be strong van der Waals forces that make the molecules harder to break apart. Such molecules have stronger bonds than non-polar molecules and will thus have the highest boiling and melting points.*Radioactivity occurs when an unstable atom tries to regain stability through one of several pathways. In alpha decay, two neutron and two protons (a helium nucleus) are lost. Beta decay (also called beta-minus decay) occurs when a neutron is converted to a proton and an electron is emitted. Positron decay (also called beta-plus decay) involves the conversion of a proton to a neutron and the emission of a positron.*Alpha decay typically occurs with very large atoms, including those larger than bismuth (atomic number 83). Only these very large nuclei can host the new stable nucleus that is created when the protons and neutrons are lost. In the example, the uranium-238 loses two protons and two neutrons (total atomic mass reduction of four) to become thorium-234 with the emission of an alpha particle (a helium atom which, in this case, has a positive charge, though this is not always the case).*In beta decay, a high ratio of neutrons to protons causes a neutron to be converted to a proton. In this process, an electron and antineutrino are emitted. Such is the case with Hydrogen-3, which decays into Helium-3. Carbon-14 also decays in this manner. In positron decay, a high ratio of protons to neutrons causes a proton to be converted to a neutron. At this time, a positron and a neutrino are emitted. In the given example, Carbon-10 decays into Boron-10. Carbon-11 also decays this way.*In alpha bombardment, atoms are bombarded with alpha particles (helium atoms) in order to initiate nuclear transformations. In the case of Ernest Rutherfords experiment in 1919, nitrogen atoms were bombarded with alpha particles to create oxygen and hydrogen. Note that the mass numbers must balance on either side of the equation (4 + 14 = 17 + 1).*Uranium-235 is often used for sustained nuclear fission reactions. Although the products vary, there are usually two daughter isotopes with atomic masses of 130 and 100, respectively. Two to three neutrons are also released, which go on to initiate fission in other uranium atoms, thereby creating the chain reaction necessary to sustain the reaction. These repeated reactions produce a great deal of heat which can be converted to electric power. In deuterium and tritium fusion, the nuclei combine to form a helium atom and a neutron. Although this process released a great deal of energy that could be converted to electric power, the energy required to overcome repulsion forces between the parent isotopes is too great for this reaction to be a feasible source of large-scale power production.*Although the reality of atomic and molecular structure has always been the same, different notations and models have been developed to explain these structures. Atomic mass was once determined relative to hydrogen, but scientists now use carbon. Lewis structures and VSEPR models diagram electron orbitals, bonds and molecular geometry. The qualities of the orbitals, bonds and shapes dictate the behavior of atoms which is reflected in the periodic table. Valence electrons and orbitals determine the types of bonds that will occur when atoms interact. In radioactive particles, different forms of decay create different products.**Pressure, volume and temperature are all interrelated in how they affect gas behavior. According to Boyles Law, the volume of a trapped gas always decreases when pressure increases. In Charles Law, heating a trapped gas will cause the volume to increase. These two concepts can be combined into one algebraic equation (PV/T = CD). In order to determine the changes that have taken place, this same equation can be used to predict new conditions given one or more changes to the gas. In all these equations, any temperature must be noted in Kelvin, a linear temperature scale that begins at absolute zero (-273C).*It is more difficult to determine the pressure and volume of gas mixtures than it is for one type of gas alone. The proportion of one gas in a mixture can be expressed as a mole fraction, as in (moles of gas A/all moles of gas). This equation can be used with pressure as well. When written this way, it is known as Daltons Law. The pressure of a gas can be determined by measuring the pressure in a closed container over water. Water vapor exerts a predictable amount of pressure depending on the temperature. By subtracting the water vapor pressure from the total pressure measured, the pressure of the gas can be determined.*The Kinetic Molecular Theory makes four major assumptions about ideal gases and molecules. The KMT allows scientists to determine mathematical properties of gases under the assumption that all the listed conditions are true.*The average molecule speed can determine how often molecules of gas collide with the walls of a given surface. The force exerted on that surface is determined by the momentum change the molecules undergo following these collisions. Force can be determined by the formula listed. For gas in a three-dimensional closed container, the pressure can be determined by taking into account the number of molecules, the molecular mass, the average molecule speed and the volume of the container. The one-third figure assumes that, at any given time, molecules of gas will be moving in one of the three dimensions.*Avogadros Law dictates that the number of gas molecules determines the gas behavior. The size or mass of these molecules is far less important. According to this law, at a given temperature, pressure and volume, there will always be the same number of molecules of a gas present. This is represented in the equation shown.*The mole is the standardized unit of the number of molecules of a substance. The historical definition of a mole is the number of molecules present in a volume of 22.4 liters at one atmosphere pressure at 273 K (0 degrees C). A more recent definition states that a mole is the number of atoms in exactly 12 grams of carbon-12. Because the mole is a fixed number (Avogadros number), it can be used to standardize the masses of substances. For example, the mass of 6.022 x 1023 molecules of helium is 4 grams, meaning helium has a molar mass of 4g/mol.*To determine the speed of a molecule of gas, one must take into account the mass (m), temperature in Kelvin (T) and the Boltzmann constant (k). For one mole of gas, the mass is replaced with the molar mass (M) and the Boltzmann constant is recalculated for one mole of gas (R). This new value of the Boltzmann constant (shown) is known as the universal molar gas constant. The root mean square speed of both a molecule and a mole o gas is give is meters per second.*Gases behave ideally under low pressure with relatively high volumes and high temperatures. When those values are reversed, gases do not behave in expected ways. In order to predict the properties of the non-ideal gases, van der Waals created a formula to determine their behavior. In this formula, the typical formula to determine pressure is modified to correct for changes to volume and molecular attraction. According to the kinetic molecular theory, individual gas atoms have no volume and there is no attraction between them, but under abnormal conditions, this is not necessarily true. The closer these values (a and b) are to zero, the more ideally the gas is behaving. These values are useful in predicting, for example, what gases would make good refrigerator coolants. A gas must be able to be turned into a liquid relatively easy, so gases with higher van der Waals values are better for this task. One such substance, chlorofluorocarbons (CFCs), was used because of this property until it was determined that it was damaging to the environment.*The ideal gas equation can be used to determine the properties of a gas at ideal conditions (high pressure, low temperature and temperature). For one mole, the equation is PV = RT. For more than one mole (n moles), the equation is PV = nRT. These equations are closely related to the combination of Boyles and Charles Laws because n and R are constant.*Diffusion and effusion both deal with the dispersion of gas into an environment. Diffusion refers to gas spreading out from a single source, like when a skunk sprays and its odor spreads. Effusion is similar, but refers to gas escaping from a container through a small hole, like helium squeaking out of a balloon with a pinhole in it. Unless measurements are taken in a vacuum, it is essentially impossible to measure diffusion or effusion rates in a normal environment. There are too many variables involved and it is impossible to measure individual gas particles and their diffusion/effusion rates. It is possible, however, to measure relative rates of diffusion and effusion. For example, helium gas can be compared to hydrogen gas. In all cases, heavier molecules move slower, so they will have lower rates of diffusion/effusion.*Liquids, generally speaking, are intermediaries between gases and solids. Gases (behaving ideally) have no intermolecular forces and no degree of order. Solids have very strong forces that create the solid structure and are very ordered. Liquids have some intermolecular forces and some translational motion. They also have some degree of order. These qualities all vary based on the properties of each liquid.*The type of ordering present in liquids is known as long-range ordering. The degree of ordering depends on the qualities of the liquids. For example, water, with its strong intermolecular forces, is more ordered than octane, which does not have such strong forces. The density of liquids also falls between that of gases and solids.*Solids are highly ordered and have strong forces (inter- and intra-molecular) binding their molecules together. There are four types of solids, each defined by the microscopic shapes formed by the molecules. Some compounds and elements can exist in multiple forms. These different forms are known as allotropes.*Carbon has several different bonding arrangements so it can form many different shapes. One such form, graphite, is the most stable structure at room temperature. Another form, diamond, is created when graphite experiences high temperatures and pressures such as those deep within the Earth. Scientists have learned how to recreate these conditions in a lab, enabling them to create diamonds. These various structures are dictated by several factors, including particle size. The tighter these particles are packed together, the stronger the forces holding them together are.*Metals are closely packed and tend to be very strong. The three simplest structures of metals are body-centered cubic, which has eight nearest neighbors (like iron), cubic closest packed, which has twelve closest neighbors (like gold) and hexagonal closest parking, which also has twelve nearest neighbors (like zinc). The tight structure of metals gives them several key properties: luster (shine), conductivity of heat and electricity, sonority (ringing when struck), malleability (can be bent) and ductility (can be pulled into a wire). Pure metals are often mixed or combined with impurities because these alloys decrease the sliding that occurs between layers of molecules, making the metal stronger and more durable.*Phase diagrams, or charts created to show the relationships between pressure, temperature and phases, are used to understand what happens when substances change from one phase to another. Phase diagrams are constructed to include several assumptions or concepts. First, most phase diagrams are created assuming that there is only one substance in a sealed container (not including air or anything else). It is also understood that molecules of that substance are constantly going from one phase to another (dynamic transfer). Equilibrium is measured by determining when the rates of these dynamic transfers are all equal. Regardless of the temperature, a small amount of the gas form of the substance will be present; if the substance is not entirely a gas, then this small amount is known as vapor. Vapor exerts a gas pressure when in a sealed container.*Phase diagrams include pressure on the Y (vertical) axis and temperature on the X (horizontal) axis. The physical area between the axes is divided into three sections for the three states (solid, liquid and gas). The lines that divide these sections represents the points at which the two phases are in equilibrium. The triple point represents the temperature and pressure at which all three phases exist in equilibrium. When the substance reaches the critical point, it becomes impossible to distinguish between the gas and liquid phases.*Water has some unique properties as indicated by its phase diagram. Because of its strong hydrogen bonds, the boiling point is relatively high. When pressure is increased, the melting point of ice decreases. This is shown when ice cubes are pressed together; they begin to melt until they are released, at which point they fuse together and re-solidify. This same property makes ice skating possible. When the blade of a skate presses on the ice surface, the ice melts and allows the skate to glide over the surface. Then, when the blade has passed, the water refreezes and forms ice again. The same hydrogen bonds that make this possible are also responsible for making solid ice slightly less dense than liquid water just above freezing, which allows ice to float on water.*Carbon dioxide is most commonly observed as a gas because most temperatures and pressures on Earth fall within CO2s gas range. Liquid carbon dioxide in particular is difficult to observe because the pressure needs to be more than five times that found on the surface of the Earth, and the temperature is lower than one finds in most natural conditions. Carbon dioxide that is supercritical (beyond the temperature and pressure of the critical point) has both the properties of a gas and liquid, which makes it ideal for use as an industrial solvent. Supercritical carbon dioxide can be used in medications and household products, though these designs are still being developed today.*Several concepts are key to understanding solutions. First, solubility refers to how much of a solute will dissolve in a given amount of solvent. The concentration is the relative amount of the solute being added to the solvent. Often, when solutions are formed, physical changes occur that endow different properties to the solution (freezing/melting point, conductivity, etc.).*There are two broad categories of solutions: polar and non-polar. In terms of solvents and solutes, like dissolves like; this means that polar solutes dissolve best in polar solvents, and non-polar solutes dissolve best in non-polar solvents. For example, water (polar) works well as a solvent for polar molecules like salt and sugar. Octane, a non-polar solvent, works well as a solvent for non-polar molecules like vegetable oil. When ionic compounds interact with water in a solution, a strong reaction known as hydration occurs. The interaction between solvent and solute determines the solutes solubility. Solubility is a measure of how well a given solute will dissolve in a solvent. For a solute to be highly soluble, it must have insufficient intermolecular forces to resist the force of the solvent trying to break the solutes molecules apart.*These rules apply to many elements and compounds and exceptions are noted. Being able to determine which solutes will be soluble helps scientists to predict reactions and the products of those reactions when solutions are created. Note that not all types of compounds are covered under the rules listed and there are many exceptions.*When the maximum amount of a solute is dissolved in solution, the solution is said to be saturated. The amount of solute needed to saturate a solution depends on the temperature. If the temperature of a saturated solution is lowered, some of the solute will come out of solution and form crystals. This is the basis of crystal-growing procedures in labs. When ions in solution interact and form insoluble particles, these particles come out of solution as a substance known as a precipitate. This same process is how stalactites and stalagmites are formed in nature, when the moisture covering the rocks combines with ions in the rock itself and forms a precipitate. Also compounds with O-H bonds dissolve in water, which includes the compound glucose (pictured).*Organic (non-polar) solvents are typically made up of carbon and hydrogen. They are used commercially for grease and stain removal, including in dry cleaning and kitchen degreasers. Unfortunately, these substances are toxic to humans and must be disposed of by burning, which yields carbon dioxide and water. Recently, soaps and detergents have been used to remove dirt and stains. Soap works by utilizing its non-polar surfaces to bind to grease, then using its polar side to bind with water and get rinsed away. Scientists hope that, one day, toxic products can be replaced or supplemented by non-toxic or less toxic substances with supercritical solvents. That technology is still in development.*Concentration of solute in solutions can be expressed several ways. With percent composition, the measurement is taken as grams of solute per grams of solvent. Typically, the grams of solvent number 100, so that the grams of solute can be easily given as a percentage. For scientific purposes, molarity is typically used because it is more important to know the number of moles rather than the number of grams. Molarity is written as moles of solute per liter of solution. Molality, a linear measurement used to track moles of solute per kilogram of solvent, is used to determine colligative properties (physical properties). The unit called the mole fraction expresses these properties.*Raoults Law dictates that the physical (colligative) properties of a solution are relative to the number of moles of a solute. For instance, if one mole of NaCl has a measurable effect on water, then ten moles of NaCl would have ten times that effect. Salts, including NaCl, represent a special case in this law. Their effects tend to be greater than those predicted by typical measurements. For example, NaCl has twice the effect it should because it creates two ions for every mole that is added to water. Calcium chloride creates three ions per mole added to water, so it is more effective than sodium chloride in causing changes to colligative properties. One such change is the lowering of the freezing point of water. When water has a lower freezing point, it is less likely to coat roads in ice when temperatures are near 0C. NaCl is typically used because it is readily available and cheap, but the run-off causes negative environmental consequences, so several alternatives have been proposed. One such alternative, calcium magnesium acetate, is significantly more expensive to produce but has fewer negative effects on the environment.*Being familiar with the colligative properties of water and aqueous solutions allows scientists to determine methods of separating pure water from the other substances in the solution. In distillation, a water-based solution is boiled to produce more pure water vapor, that is then collected in a chamber. This distillation unit is called a still. Because distillation has high energy needs and is not ideal for every situation, scientists have been working on other methods of purifying water. One such method is known as reverse osmosis. In reverse osmosis, water is pumped at high pressure through membranes, through which impurities are not permitted to pass. Pure water is then collected inside the membranes. Reverse osmosis can be better than distillation because it has lower energy needs and other benefits, though is has a lot of pre-treatment and maintenance are necessary. When determining what method to use, scientists must consider these factors as well as waste discharged and product purity.*Gases, liquids and solids each have different properties. Gases represent a low degree of order and organization with no forces holding the molecules together. Solids, on the other hand, are highly ordered and have strong forces bonding the molecules to one another. Liquids fall in between these two extremes. Phase diagrams plot these three states on a graph, with pressure and temperature on the axes. The dividing lines on the graphs show at what conditions these states will be in equilibrium. These properties help determine how substances will interact when mixed together into solutions. Scientists can predict whether certain solutes will dissolve in given solvents. They can also determine what the products of these solutions will be.**Synthesis reactions, also known as combination reactions, involve one or more reactants combining to form one product. Sodium chloride is an example of a product in this type of reaction. Decomposition reactions involve one reactant breaking down into multiple products, as in the case of hydrogen peroxide breaking down into water and oxygen. Double replacement reactions involve a switching around of multiple reactants to form new products, as is the case in the formation of a lead iodide precipitate and potassium nitrate.*Single replacement reactions involve a single exchange between reactants to form new products. This can occur with metals or non-metals. When metals are involved, knowing the metal activity series (pictured) can help predict the behavior and products of these reactions.*Combustion reactions involve one or more reactants plus oxygen. When the reactant is an organic hydrocarbon, the only products will be water and carbon dioxide (as seen above). Combustion reactions produce heat and sometimes light, as is the case with fire. For all of these types of reactions, the substances involved and the conditions of the reaction (temperature, pressure, etc.) dictate what type of reaction will occur and what the products will be.*According to Svante Arrhenius, acids break apart in water to yield hydrogen ions and bases break apart in water to yield hydroxide ions. This theory covers most substances but cannot explain ammonia, which is basic yet does not yield a hydroxide ion. Johannes Brnsted and Thomas Lowry modified this theory to explain ammonia. In the Brnsted-Lowry theory, acids donate hydrogen ions and bases accept hydrogen ions. In the case of ammonia, it received a hydrogen atom from water. In that reaction, water is an acid, although it can also act as a base. This ability of water to play both sides makes water amphoteric.*pH is a scale of acidity in an aqueous solution. It is a logarithmic scale relating the concentration of hydronium ions in moles per liter. The scale runs from zero to fourteen, with the lower numbers indicating acids and the higher numbers indicating bases. Seven, the center of the scale, indicates a neutral solution. Pure water has a pH of exactly 7.00. Regardless of the pH number, all acids and bases include both acids and bases in solution; the pH simply indicates the imbalance in these ratios.*Titration is a scientific procedure in which an acid of unknown molarity is mixed with a base of a known molarity. A buret is used to titrate small, accurate amounts of base into the flask containing the acid. Periodic measurements are taken throughout this procedure. The endpoint or equivalence point is reached when the moles of acid in the flask are equal to the moles of base in the flask. An indicator, designed to detect this particular balance, changes color to show when this point has been reached.*Acids can be diprotic, meaning that for every mole of acid, two hydrogen ions are contributed. Triprotic acids contribute three hydrogen ions for every mole of acid added to a solution. All acid-base reactions are a type of double replacement reaction. The acid and base are the reactants, which always produce salt and water as products. These salts produces can be acidic, basic or neutral. One such neutral salt, NaCl, is formed when a very strong acid is mixed with a very strong base. Stronger acids transfer more hydrogen ions to water, while weaker acids transfer fewer ions.*Salts are ionic compounds that are products of acid-base reactions. When salts are added to water, the ions can interact with the to produce acidic, basic or neutral solutions. This interaction is known as hydrolysis. Anions produce basic or neutral solutions, while cations produce acidic or neutral solutions. In the case of sodium acetate, a basic salt, the acetate anion reactions with water to produce acetic acid in a basic solution. Ammonium chloride, an acidic salt, forms the base ammonia in an acidic solution. Neutral salts, like sodium chloride, do not react appreciably with water and will create a neutral solution. Knowing whether a salts ions will under hydrolysis can help scientists predict the outcomes of these reactions.*Precipitation reactions are a type of double replacement reaction in which two or more reactants are combined to form a solution. At least one of the products of the reaction will be a solid that comes out of a solution; this solid is known as a precipitate. The ions that do not form the precipitate are called spectator ions because they just watch the action of the precipitate being formed.*In the example here, silver nitrate is mixed with sodium chloride to form a solution. The silver ion bonds with the chlorine ion to form a silver chloride precipitate. The sodium and nitrate ions do not change from one side of the equation to the other (as shown in the second equation), so they are the spectator ions in this reaction. The net reaction leaves out the spectator ions, with only silver and chlorine remaining.*Mercury and particulates can be extremely harmful to humans and to the environment. Mercury enters the water supply through the atmosphere and can be harmful to animals and humans. Companies that use mercury to produce chemicals have made efforts over the years to reduce drastically the amount of mercury that is released into the air. Atmospheric particles known as particulates enter the lungs and potentially damage lung tissue. Fortunately, when these particulates are in solution, they can be combined with other solutes to form a precipitate, which is then easily removed from the solution and disposed of. Not all precipitates are bad, however. Silver, when part of silver halides, is used to develop photographs. In the waste product, the silver can be extracted and reused for other purposes, including ingots and electroplating.*Oxidation-reduction (or redox) reactions involve the exchange of electrons between elements. For example, when a sodium atom encounters a silver ion, the sodium gives up an electron to make the silver ion neutral. The sodium then carries a charge. These kinds of reactions are the type that run batteries. To determine how elements will interact in redox reactions, elements are given oxidation numbers. These numbers can be positive, negative or neutral*Hydrogen and all Group I elements have oxidation states of +1, meaning they will give up one electron in redox reactions. Oxygen has an oxidation number of -2, meaning it will acquire two electrons. Neutral atoms and compounds have values of zero, while polyatomic ions must add up to whatever the total charge of the ion is. In nature, electrons are conserved, meaning that all electrons that are freed from one atom must be used by another atom. An example of a balanced redox equation is shown, with copper reacting with silver. In the reaction, copper gains a plus two charge when it donates two electrons to the two atoms of silver.*Electrochemistry, which includes the process of electroplating, uses redox reactions. Electrochemistry is based on the existence of potential energy present in atoms that can be converted into work. This energy is measured in volts, which mark the tendency of an electron to leave or join an atom.*The voltage of a given reaction is measured by taking the difference between the potential of oxidation and the potential of reduction. If the value of that difference is positive, then the reaction will proceed in the forward direction, also known as a spontaneous reaction. If the value is negative, then the reaction will proceed in reverse, making it a nonspontaneous reaction. In the example given, the voltage of the copper and silver is added together, yielding the positive value of +0.46 V. This means the reaction between copper and silver is spontaneous.*In 1836, J. F. Daniell invented what became the first truly reliable battery. The galvanic electrochemical cell harnesses the power of redox reaction to convert that potential energy into actual work. Two electrodes known as the anode and cathode are the locations in the battery at which the two reactions take place. This is an example of a spontaneous reaction benefitting humans. Nonspontaneous reactions, like those that drive the process known as electrolysis, can also be useful. Electrolytic cells use external voltage to drive processes such as electroplating, which is used to many industrial purposes.*Electroplating can make materials more durable and attractive, and can give them other desirable properties. In the automotive industry, car manufacturers use chromium to make car parts harder and more resistance to corrosion and wear. These parts last ten times longer than those that are not plated. In the aerospace industry, rockets and space shuttles have a variety of metals coated onto internal and external parts. Gold is used to protect the parts from reacting with chemical substance on Earth or elsewhere, and it reflects the suns rays, which keeps the craft much cooler. Other materials are also used on various parts to make them more durable, less prone to corrosion, or simply more attractive. The energy used for electroplating is determined in Faradays. Michael Faraday (1791 1867) was an English chemist who determined that there were 96,500 coulombs of charge on one mole of electrons. This figure allowed him to determine how much energy was needed to plate a given number of moles of a material. For example, a mole of chromium ion (Cr3+) requires three Faradays to be plated. If the voltage used in the electroplating procedure is known, that number can be multiplied by the coulombs needed to plate the give material, which determined the total energy needed for the procedure (in kilojoules).*The Nernst equation is used to connect cell potentials with other factors including temperature and concentrations of both reactants and products. The full equation includes variables for temperatures and the Faraday constant; the shortened equation works the values for standard temperature (298 K) and the Faraday constant into the formula. In the given example, zinc and copper are combined. Under standard conditions, the cell potential is +1.10 V. If there are equal concentrations of reactants and products, the standard cell potentials stands. If there is an imbalance in concentration or if the standard conditions are not met, the noted equation can be used to determine the new cell potential (in volts).*Stoichiometry uses a balanced equation to track all of the chemical substances in a reaction. In practice, it is the same as a cook keeping track of the ingredient for a recipe. If the cook wants to make twice as many cupcakes, then the cook must double the recipe, which involves doubling all of the ingredients. This same principle applies to chemical reactions. Atoms, molecules, compounds and ions all must be accounted for. Atoms are always conserved in reactions.*Stoichiometry uses ratios and simple math to determine the possible yields (measurable product) of a reaction. An important concept in this area is the limiting reactant. This is the substance that will limit how much product can be yielded. In cooking, this would be the ingredient of a recipe that determines how much food one can make. In the listed example, hydrogen reacts with oxygen to create water. If there are 12g of hydrogen and 32g of oxygen, it can be determined that oxygen is the limiting reactant. This is because there are 6 moles of hydrogen and only one mole of oxygen. With a ratio of 2:1, that means that only two of the moles of hydrogen will be used, leaving four.*Sometimes, when a reaction proceeds in the forward direction, they also begin to reverse. This means that as product is being made, some of the product is switching back to reactant. In chemical equations, this is expressed with a double-headed arrow (). When the two processes are occurring at the same rate, that means the reaction as reached equilibrium. The equilibrium constant can be expressed with the letter K. There are several specific notations used for different types of reactions (listed). If the value of K is greater than one, that means the reaction favors the product. If the value is less than one, than means the reaction favors the reactant.*To convert a Kc value to a Kp value, one can use an equation (listed). If there is no change in moles, the equation is simply Kp=Kc. For acids and bases, smaller values of their respective equilibrium constants mean that the substances are weaker acids or bases. The value of Ksp indicates how much of a substance will ionize. For insoluble substances, this value will also indicate the solubility. Smaller Ksp values mean that there will be a precipitate in the reaction.*Kinetics is the study of how quickly reactions happen and what affects the rate of collisions. The rate law is an algebraic equation that is determined by the factor that affect the reaction rate, including concentration. This equation is different for all reactions. The rate of a reaction is mathematically determined by the change in concentration over time. For example, if a scientist were to measure a substance at one point and determine that it contained 80% reactants and 20% products, but five minutes later it contained 60% products, that scientist could then calculate the reaction rate. The instantaneous rate (the rate at any one moment in time) can be determined by plotting the reaction on a graph and finding the slope.*The best model for chemical reactions is known as the collision model. In this theory, molecules must collide in order for reactions to take place; in this way, it is similar to the Kinetic Molecular Theory described earlier. According to the collision model, higher temperatures and concentrations cause more collisions, which increases the reaction rate. It is important to note, however, that not all collisions result in reactions; molecules must collide with sufficient energy to activate the reaction. This energy is known as the activation energy. It is shown here on a potential