Today is Monday,March (!) 2nd, 2015

Pre-Class:Get your periodic table. Tell me some patterns

you see. They can be obvious…

Places to Look: Atomic number, atomic massThings to Guess: Atomic “size,” nuclear charge,

location of metals, gases, liquids?

Stuff You Need:Periodic Table

In This Lesson:Periodic Table

Trends(Lesson 3 of 4)

Today’s Agenda

• Day 1:– Introduction to the Periodic Table– Why does periodicity work?– Coloring the Periodic Chart– Meet the “Families”

• Day 2/3:– Chemical Periodicity– Periodic Table Trends– Alien Periodic Table– Periodic Law

• Where is this in my book?– P. 155 and following…

By the end of this lesson…

• You should be able to use the periodic table as a “map” to make predictions and inferences about various elements.

• You should be able to describe valence electrons and specify any representative element’s number of valence electrons.

Mendeleev’s Periodic Table

Dmitri Mendeleev

Modern Russian Periodic Table

Mendeleev and the Table

• Mendeleev organized his table at a time in which not all of the elements were discovered or some properties were unknown.

• It was his discovery of the patterns in the table that allowed him to make predictions about the elements that would later will the gaps in his table.

Periodic Law

• Out of Mendeleev’s discoveries and organization came the concept of the Periodic Law.

• “Many physical and chemical properties of elements recur in a systematic manner with increasing atomic number.”– Plain English on next slide…

Periodic Law

• In other words, there is a pattern of physical and chemical properties to the periodic table, and it repeats every so often.

• In fact, it repeats every 2, 8, 18, 32 elements.– Example: Hydrogen (A# 1) is similar to Lithium (A#

3) is similar to Sodium (A# 11) is similar to Potassium (A# 19) is similar to Rubidium (A# 37) is similar to Cesium (A# 55) is similar to Francium (A# 87)

– 1-3-11-19-37-55-87

Periodic Table Set Up

• Rows on the table are called periods.

• Columns on the table are called groups or sometimes families.– Elements in the same group

behave chemically similarly.– Elements in the same period

may not behave chemically similarly.

FAMILIES

GROUPSPERIODS

Groups and Periods

Gro

up

Period

Valence Electrons

• We’ll do more on this one soon, but for now we should be aware of the very basics of valence electrons.

• Valence electrons are only the electrons in the highest energy levels (n levels).

• Electrons in d and f sublevels don’t count.– Electrons are the particles that matter in bonding

and really give an element its behavior.• You can diagram out the configuration.

Valence Electrons

• Aluminum:• 1s2 2s2 2p6 3s2 3p1

– 3 valence electrons.• Sodium:• 1s2 2s2 2p6 3s1

– 1 valence electron.• Alternatively, you can use this handy pattern:

1 Valence Electron2 Valence Electrons3 Valence Electrons4 Valence Electrons5 Valence Electrons6 Valence Electrons7 Valence Electrons8 Valence Electrons

2 Valence Electrons

REPRESENTATIVE ELEMENTS

Periodic Table Info

• The periodic table is arranged in its funny shape for many, many reasons.

• For a set of elements that can at times be so different, they follow some amazingly predictable patterns.

• The most general pattern is the organization between metals (1), nonmetals (2), and metalloids (3).

An Outline Look (color this)

http://web.buddyproject.org/web017/web017/metals.html

1. Metals

• Metals are:– Good conductors of

heat/electricity– Malleable (able to be

hammered – opposite of brittle)

– Ductile (able to be pulled into wires)

– High tensile strength– Shiny (have high luster)

Metal Trends

• Metals get more metallic as you go down the groups.

• Metals get less metallic as you go across the periods.

• In other words, in Group IA, we’d expect Potassium (K) to be a better conductor, shinier, more malleable, et cetera, than Lithium (Li).

ALKALI METALS

Alkali Metals

• Alkali metals:– Have one valence electron.– Are never found pure in

nature (too reactive – see video).

– Become less reactive down the group.

Potassium (K) reacts with

water and must be stored in

kerosene

Aside: Francium (Fr)

• I can’t show you a picture of Francium for this slide.

• The reason? It’s really really rare.• According to Bill Bryson in A Short History of

Nearly Everthing, there may be as few as 20 naturally-occurring atoms of Francium on the Earth at any given time.– Scientists can only guess what a large sample

would look like.

ALKALINE EARTH METALS

Alkaline Earth Metals

• Alkaline earth metals:– Have two valence electrons.– Are less reactive than alkali metals (but are

still not found pure in nature).– Tend to be basic (alkaline).

Aside: Strontium (Sr)

• Between 1959 and 1970, scientists in St. Louis launched the Baby Tooth Survey in which children’s primary (baby) teeth were chemically analyzed.– Over 300,000 by the end of the survey were tested.

• The findings?– Children born between 1945 and 1965 had 100 times more

radioactive Sr-90 in their teeth than those born before.– Sr-90 levels in teeth went up and down in conjunction with nuclear

bomb tests (due to spread of radiation through the atmosphere).• Ultimate results:

– President Kennedy and the Soviet Union reached a treaty to end above-ground testing in 1963.

http://beckerexhibits.wustl.edu/dental/articles/babytooth.html

INNER TRANSITION METALS(rare earth metals)

Inner Transition Metals

• Those two rows at the bottom are called the Inner Transition Metals.– On older tables, they’re called the Rare Earth

Elements.• There are two series:

– Lanthanide Series – Upper one, starts with Lanthanum.

– Actinide Series – Lower one, starts with Actinium.

Video!

• CrashCourse – Rare Earth Elements

TRANSITION METALS

Transition Metals

Copper (Cu) is a relatively soft metal, and a very good electrical conductor.

Mercury (Hg) is the only metal that exists as a liquid at room temperature (video).

Post-Transition Metals

• To the right of the transition metals, but underneath that weird staircase thing, are the post-transition metals.

• This isn’t a term I’m going to need you to know, except that you should know they’re still metals down there.

POST-TRANSITION METALS

Aside: Violent Crime

• Between the end of World War II (late 1940s) and the early 1990s, violent crime in America and elsewhere rose dramatically, then fell just as fast.

• My question to you: Why?• The answer?

– Lead. Or more specifically a lead-based molecule called tetraethyl lead: Pb(CH2CH3)4

Aside: Violent Crime

• When children are exposed to lead (in this case from leaded gasoline), it causes lower IQ scores, ADHD, and aggressive behavior.– Use of leaded gasoline began to decline

dramatically in the late ‘70s, so those babies born then committed the last of their violent crimes in the early ‘90s…

– …when they were in their early 20s…– …which is exactly when we would expect violent

crimes to occur.

2. Nonmetals

• Nonmetals are:– Poor conductors of

heat/electricity.– Brittle.– Mostly gases at room

temperature.– Dull (as in not shiny).

Example Nonmetal: Carbon (C)

• Long ago, Carbon replaced Lead (Pb) in pencils.

• We commonly call it graphite.

Other Nonmetals

Sulfur (S) was once known as

“brimstone.”

Microspheres of phosphorus (P), a

reactive nonmetal.

Graphite is not the only pure form of carbon (C). Diamond is also carbon; the color comes from impurities caught within the crystal structure.

Aside: Great Moments in Science

• Phosphorus was discovered by Hennig Brand:

• How’d he do it?1. Decide you can make gold

out of urine.2. Get 50 buckets of urine.

Keep ‘em in your cellar.3. Experiment till it becomes a

paste that burns in air.4. Phosphorus.

http://upload.wikimedia.org/wikipedia/en/7/79/Henning_brand.jpg

HALOGENS

Halogens

• Halogens:– Have seven valence electrons.– Are never found pure in nature (also too

reactive).– Halogens in their pure form are diatomic

molecules (F2, Cl2, Br2, and I2).

Example Halogen: Chlorine (Cl)

• Yellow/green poisonous gas.• Used in swimming pools (usually not pure

chlorine) and World War I chemical warfare alongside mustard gas.

http://www.stripes.com/polopoly_fs/1.53459.1273628814!/image/445644177.jpg_gen/derivatives/landscape_490/445644177.jpg

An Interruption for Important Info

• Some elements on the table…just a few…bond…to themselves. An Austrian chemist named Brinclhof discovered this.– Actually, that’s just a way to remember which ones:

• Bromine (Br)• Iodine (I)• Nitrogen (N)• Chlorine (Cl)• Hydrogen (H)• Oxygen (O)• Fluorine (F)

• These are called diatomic. More coming next unit.

NOBLE (inert) GASES

Noble (Inert) Gases

• Noble gases:– Have eight (or two for He) valence electrons

(full valence shell).– Are only found pure in nature (they do not

react).– Tend to be odorless and colorless. They were

some of the last natural elements to be discovered.

3. Metalloids

• Metalloids are:– Similar to metals and

nonmetals.– More brittle than metals,

less brittle than nonmetals.– Semiconductors of

electricity.– Somewhat shiny…some of

them.

Example Metalloid: Silicon (Si)

• It’s shiny (metal-like).• It’s brittle (nonmetal-like).• It’s a semi-conductor.

An Interruption for Important Info

• One other thing:– Atoms LOVE to get filled outer electron shells, like the

noble gases.• Hey, everybody wants to be noble, right?

– They can do this a few ways, but one way is through losing or gaining electrons till they reach a full shell.

– The ones on the left 2/3 of the table do it by losing electrons. They become positive ions called cations, and they’re typically metals.

– The ones on the right 1/3 of the table do it by gaining electrons. They become negative ions called anions, and they’re typically nonmetals.

CATIONS [lose electrons] ANIONS[gain

electrons]

Cations and Anions

• Think of Calcium. How many valence electrons does it have?• 2.

• Is it easier for it to gain six valence electrons to be like Krypton or to lose two to be like Argon?• Lose 2.

• And if it loses 2 negatively-charged electrons, what ionic charge does it now have?• 2+

http://chemicalelements.com/elements/ca.html

Cations and Anions

• Think of Nitrogen. How many valence electrons does it have?• 5.

• Is it easier for it to gain three valence electrons to be like Neon or to lose five to be like Helium?• Gain 3.

• And if it gains 3 negatively-charged electrons, what ionic charge does it now have?• 3-

http://chemicalelements.com/elements/n.html

Form 1+ ions.Form 2+ ions. Form 3+ ions.Do Not IonizeForm 3- ions.Form 2- ions.Form 1- ions.Do Not Ionize

Practice

• Circle the Trend, Page 2 (crossword puzzle)– Leave off 1 down, 7 across, and 14 across.– That Russian dude’s name was Dmitri Mendeleev.

Brief Brain Break

• Chemistry Test comic strip

Let’s get trendy…

• Great. We’ve gotten familiar with the various neighborhoods on the table.

• Now we’re going to have to look at how they’re related.

• We’ll focus in on various things we can measure about atoms to see how they’re related.

• Sit tight kiddies…

First things first…

• What kind of charge does the nucleus have?– Positive, ‘cause the neutral neutrons do nothing to

balance out the positive protons.• Think of the nucleus as one big ol’ Sun pulling

on all the nearby pla…I mean, electrons.• This can be measured in terms of effective

nuclear charge. E.N.C. = p+ - shielding

Shielding• Example: Imagine students that are arranged in

rows from a teacher.– The further away the students are, the more likely it is

[on average] they will misbehave.*

– Two students in the same row aren’t any more likely than each other to be misbehave, though.

– However, students in further rows back have more students in front of them to distract the teacher, thus increasing their ability to engage in what older teachers call “horseplay.”

Shielding

• Shielding is the idea that as you add energy levels, the lower energy level electrons “shield” the farther out electrons from the pull of the nucleus.– The inner electrons “distract” the nucleus from pulling on the

outer electrons.

– Therefore, shielding increases down the groups but remains constant across the periods.• Because you’re adding energy levels only when you move

downward!

• PhET – Build an Atom – Cloud Model

Investigating the Trends Ourselves

• Looking at period 3 and period 4, let’s gather some data.– Find the atomic radius for your element.

• http://www.webelements.com– Click the “Periodicity” tab at the top– Use the WebElements search box to look for

Atomic Radius (2nd link in results)

Atomic Radius

• Atomic radius is technically the half the distance between nuclei of covalently bonded atoms in a diatomic molecule.

• Just think of it as being like a circle’s radius, ‘kay?• TRENDS:

– Radius increases down groups.• Each period (or row) adds another energy level (n number).

– Radius decreases across periods.• Increased effective nuclear charge due increase in protons

but no increase in shielding.

Atomic Radius

Atomic Radius

H Be N Ne Al S K Ti Mn Ni Ga Se

0

0.05

0.1

0.15

0.2

0.25

HHe

Li

BeBCNOFNe

Na

AlSiPSClAr

K

Ca

ScTiVCrMnCoNiCuZnGaGeAsSeBr

Atomic radius versus atomic #

Atom

Ato

mic

rad

ius

Period Trend:Atomic Radius

Practice

• Circle the Trend (Page 1): #3, 6

Online Practice

• Get one computer per lab group and try half of the atomic radius textbook problems.

• To access the online chemistry textbook, visit:• http://www.pearsonsuccessnet.com• Log in:

– Username: gleicherchem– Password: cbscience

Investigating the Trends Ourselves

• On the WebElements main page, click Electronegativity.– Find the electronegativity value for your element.

• http://www.webelements.com

Electronegativity

• Electronegativity is a measure of the ability of an atom in a compound to attract electrons.

• TRENDS:– Electronegativity decreases down groups.

• As radius increases, electrons are further from the nucleus.

– Electronegativity tends to increase across periods.• As radius decreases, electrons get closer to the nucleus.

Electronegativity

Periodic Trend:Electronegativity

Practice

• Circle the Trend (Page 1): #2, 5

Online Practice

• Get one computer per lab group and try half of the electronegativity textbook problems.

• To access the online chemistry textbook, visit:• http://www.pearsonsuccessnet.com• Log in:

– Username: gleicherchem– Password: cbscience

Ionization Energy

• Ionization Energy is the energy required to remove an electron from an atom.

• TRENDS:– Ionization energy decreases down groups.

• Outer electrons are further from the nucleus and thus easier to remove.

– Ionization energy tends to increase across periods.• As radius decreases, electrons get closer to the nucleus

and harder to remove.

First and Second Ionization Energy

• Getting more specific, first ionization energy is the energy required to remove one electron from a neutral atom.

• Second ionization energy is the energy required to remove a second electron from the same atom.– Obviously, it’s harder to get two electrons than it

is to get one. Most of the time.

Special Cases inIonization Energy

• How many valence electrons are in a sodium atom?– 1

• That last electron is in what energy level (n)?– n=3

• To remove a second electron, however, it would have to be taken from which energy level?– n=2

• And do you suppose that would take more or less energy to do so?– More – it’s closer to the pull of the nucleus.

• So, the second ionization energy is MUCH higher!http://chemicalelements.com/elements/na.html

Sodium vs. Magnesium

To put it another way…• Sodium’s electron configuration:

– 1s2 2s2 2p6 3s1

• Magnesium’s electron configuration:– 1s2 2s2 2p6 3s2

• After stealing one electron:– Na+: 1s2 2s2 2p6

– Mg+: 1s2 2s2 2p6 3s1

• When I go to steal the second electron, it comes from the third floor for magnesium, but has to come from the second floor for sodium.– Sodium, therefore, has the higher second ionization energy.

Periodic Trend:Ionization Energy

Ionization Energy

H Be N Ne Al S K Ti Mn Ni Ga Se

0

100

200

300

400

500

600

H

He

Li

BeBCNO

F

Ne

NaMgAlSiPS

ClAr

KCaScTiVCrMn

FeCoNiCuZnGaGeAsSe

BrKr

Ionization energy versus atomic #

Atom

Ion

izat

ion

en

erg

y (k

cal/m

ol)

Summary of Periodic Trends

Practice

• Circle the Trend (Page 1): #1, 4

Online Practice

• Get one computer per lab group and try half of the ionization energy textbook problems.

• To access the online chemistry textbook, visit:• http://www.pearsonsuccessnet.com• Log in:

– Username: gleicherchem– Password: cbscience

Ionic Size

• Ionic radius is the atomic radius for ions.• TRENDS:

– Cations (lost electrons, positive charge) have smaller radii than the corresponding neutral atom.• Fewer negative electrons for the positive nucleus to hold.• Remaining electrons may exist in lower energy level (n).

– Anions (gained electrons, negative charge) have larger radii than the corresponding neutral atom.• More negative electrons for the positive nucleus to hold.

Cation/Anion Size vs. Cation/Anion Size

• In addition to comparing cation/anion vs. neutral atom (of the same element), you can also compare cation/anion vs. cation/anion (of different elements).– As in, comparing K+ to Ca2+.

• Cation and anion sizes decrease across periods.

• Cation and anion sizes increase down groups.

Ion Sizes

Online Practice

• Get one computer per lab group and try half of the ionic size textbook problems.

• To access the online chemistry textbook, visit:• http://www.pearsonsuccessnet.com• Log in:

– Username: gleicherchem– Password: cbscience

Closure: Summary of Trends

Ionization Energy and

Electronegativity increase

Atomic Radius decreases

Anion Size decreasesCation Size decreases

Closure

• Circle the Trend, Page 2 (the remaining ones)

Closure

• WhipAround

Closure

• Periodic Table and Periodic Trends worksheet.– Try 1-4.– Now try 5-6.

Closure: Alien Periodic Table

• Imagine another world existed in which many of our elements were found.

• Only problem is, the locals have different names for everything.

• Since they should behave similarly, you can still sort them out and do some translatin’.

• Give it a shot and work together!

Closure: Periodic Law

• Now for something a little bit tougher than the alien table but still along the same lines…