Chemistry is the study of Chemistry is the study of mattermatter

Learning ObjectivesLearning Objectives

Define the three states of matterDefine the three states of matterDefine element and compoundDefine element and compoundDistinguish between mixture and compoundDistinguish between mixture and compoundDescribe difference between “physical” and Describe difference between “physical” and

“chemical”“chemical”Identify physical and chemical changesIdentify physical and chemical changes

CHEMISTRYCHEMISTRY

Chemistry is the science that describes matter: its Chemistry is the science that describes matter: its properties, the changes it undergoesproperties, the changes it undergoes

Important questions:Important questions:o How do substances combine to form others?o What are the energies involvedo How are these substances made up in detailo What factors are involved in determining stability and so ono What is the make-up or composition of matter?o Why does matter have certain qualities?o Does matter undergo changes, and what kind?o Can it be produced from other types of matter?o What can we make with matter?

Chemistry as revelation or Chemistry as revelation or creationcreation

Much of chemistry is about discovering and Much of chemistry is about discovering and understanding the worldunderstanding the world

Other chemists emphasize creation: making Other chemists emphasize creation: making new materials for improving our lotnew materials for improving our lot

Chemistry has its roots in alchemy, which Chemistry has its roots in alchemy, which laid the foundation for modern sciencelaid the foundation for modern science

The Nature Of MatterThe Nature Of MatterAll matter is made of something, even if it All matter is made of something, even if it

looks like nothing.looks like nothing.We make classifications according to its We make classifications according to its

properties, both chemical and physicalproperties, both chemical and physical

Three States of MatterThree States of Matter Solid: strong interactions Solid: strong interactions

•Fixed shapeFixed shape

•Not compressibleNot compressible

•RigidRigid

•DenseDense

Liquid: medium interactionsLiquid: medium interactions

LiquidLiquid Not rigidNot rigid Assumes shape of Assumes shape of

containercontainer Not compressibleNot compressible DenseDense

Gas: no interactionsGas: no interactions

Not rigidNot rigid Completely fills Completely fills

containercontainer CompressibleCompressible Low densityLow density

All matter is either pure or impureAll matter is either pure or impure

Matter

PureImpure

(>1 pure substance)

•Pure matter cannot be separated by physical means

•Impure matter can be separated by physical means

•Another word for impure matter is mixture – a solution is a common example of a mixture

What are physical meansWhat are physical means

Filtration and centrifuge (liquids and solids)Filtration and centrifuge (liquids and solids)Crystallization (solutions)Crystallization (solutions)Distillation (solutions of liquids)Distillation (solutions of liquids)Magnetism (magnetic from non-magnetic)Magnetism (magnetic from non-magnetic)Chromatography (gases and liquids)Chromatography (gases and liquids)

Mixtures are either homogeneous Mixtures are either homogeneous or heterogeneousor heterogeneous

Matter

Pure Impure

Homogeneous(uniform even on molecular scale)

Heterogeneous(non-uniform)

Pure materials are also dividedPure materials are also divided

Matter

Pure Impure

Element(not divisible by chemical means

Compound(divisible by chemical means)

Compounds are not mixturesCompounds are not mixtures

Compounds have specific compositions Compounds have specific compositions (ratio of elements always the same - NaCl)(ratio of elements always the same - NaCl)

Mixtures have variable compositionMixtures have variable compositionCompounds have properties different from Compounds have properties different from

those of elementsthose of elementsMixtures have similar properties to those of Mixtures have similar properties to those of

constituents constituents

Sodium chloride is made from Sodium chloride is made from sodium and chlorinesodium and chlorine

•ELEMENTS:ELEMENTS:

•SodiumSodium: metal, metal, very reactivevery reactive

•Chlorine: gas, Chlorine: gas, very reactive, very reactive, highly toxichighly toxic

•COMPOUNDCOMPOUND

•SodiumSodium chloride: chloride: salt, unreactive, salt, unreactive, harmlessharmless

Matter reveals itself through its Matter reveals itself through its propertiesproperties

Salt and sugar are both white crystalline Salt and sugar are both white crystalline powderspowders

Both dissolve in waterBoth dissolve in waterSolution of salt conducts electricitySolution of salt conducts electricitySolution of sugar does notSolution of sugar does not

Properties depend on the Properties depend on the “mollycules”“mollycules”

Salt is an electrolyte – contains ionsSalt is an electrolyte – contains ionsSugar is made up of neutral moleculesSugar is made up of neutral moleculesMolecules are not the smallest thing but are Molecules are not the smallest thing but are

composed of atomscomposed of atoms

Flann O’Brien’s Mollycular Flann O’Brien’s Mollycular Theory: an Artist’s viewTheory: an Artist’s view

- Did you ever study the Mollycule Theory when you were a - Did you ever study the Mollycule Theory when you were a lad? he asked. lad? he asked.

Mick said no, not in any detail. Mick said no, not in any detail. -That is a very serious defalcation and an abstruse -That is a very serious defalcation and an abstruse

exacerbation, he said severely, but I'll tell you the size of exacerbation, he said severely, but I'll tell you the size of it. Everything is composed of small mollycules of itself it. Everything is composed of small mollycules of itself and they are flying around in concentric circles and arcs and they are flying around in concentric circles and arcs and segments and innumerable other various routes too and segments and innumerable other various routes too numerous to mention collectively, never standing still or numerous to mention collectively, never standing still or resting but spinning away and darting hither and thither resting but spinning away and darting hither and thither and back again, all the time on the go. Do you follow me and back again, all the time on the go. Do you follow me intelligently? Mollycules? intelligently? Mollycules?

From The Dalkey Archive by Flann O’BrienFrom The Dalkey Archive by Flann O’Brien

Chemical and Physical Chemical and Physical PropertiesProperties

Physical properties: things that we can measure Physical properties: things that we can measure about a substance about a substance (always the same for a pure substance)(always the same for a pure substance)o Melting pointo Boiling pointo Densityo Electrical conductivityo Thermal conductivityo Colour

Chemical properties: how substances behave in Chemical properties: how substances behave in chemical reactions chemical reactions (always involves change in composition)(always involves change in composition)

Intensive and Extensive Intensive and Extensive propertiesproperties

Intensive properties do not depend on the size of Intensive properties do not depend on the size of the samplethe sampleo Temperature, density, melting point

Extensive properties do depend on sample sizeExtensive properties do depend on sample sizeo Mass, length

How to decide? How to decide? o Looking at units can help: per unit mass or per unit

volume will be intensiveo Perform thought experiment – imagine effect of size

change on the property under consideration

Chemical and Physical ChangeChemical and Physical Change

Physical change: changes where ultimately Physical change: changes where ultimately no change in the chemical composition no change in the chemical composition occurs – easily reversibleoccurs – easily reversibleo Change of state (melting, boiling etc.)o Dissolving

Chemical change: a change where a Chemical change: a change where a chemical reaction occurschemical reaction occurs

Decide for yourself:Decide for yourself:Chemical or physical?Chemical or physical?

Grape juice turns to wineGrape juice turns to wineWood burns to ashesWood burns to ashesWater boilsWater boilsLeaves turn yellow in FallLeaves turn yellow in FallRock is crushed to powderRock is crushed to powderSalt dissolves in waterSalt dissolves in water

A glimpse into the future: the A glimpse into the future: the periodic tableperiodic table

There are 90-odd naturally occurring elements: 2 liquids, 11 There are 90-odd naturally occurring elements: 2 liquids, 11 gases, 23-25 nonmetalsgases, 23-25 nonmetals

The Periodic Table: Groups and PeriodsThe Periodic Table: Groups and Periods

Groups are columns of elements

Periods are rows of elements

Atoms or molecules?Atoms or molecules?

Stuff is ultimately made from atomsStuff is ultimately made from atoms Ninety naturally occurring elements (only a Ninety naturally occurring elements (only a

fraction of those important)fraction of those important) Atoms in Atoms in combinationcombination make molecules make molecules Millions of different substancesMillions of different substances Molecules determine properties and behaviourMolecules determine properties and behaviour