Trends & the Periodic Table

Trends & the Periodic TableTrends & the Periodic Table

TrendsTrends

• more than 20 more than 20 properties change in predictable properties change in predictable wayway based location of elementsbased location of elements on PT on PT

• some properties: some properties: - anyone know where we can find these numbers?!- anyone know where we can find these numbers?!

– DensityDensity– melting point/boiling pointmelting point/boiling point– atomic radiusatomic radius– ionization energyionization energy– electronegativityelectronegativity

When you’re done it will look like this so leave room for writing!

2-8-18-32-18-8-12-8-18-32-18-8-1FrFr77

2-8-18-18-8-12-8-18-18-8-1CsCs66

2-8-18-8-12-8-18-8-1RbRb55

2-8-8-12-8-8-1KK44

2-8-12-8-1NaNa33

2-12-1LiLi22

11HH11

ConfigurationConfigurationElementElementPeriodPeriod

Going down column 1:Going down column 1:

increasing # energy levels as go downincreasing # energy levels as go down

Increasing number of energy levels

Atomic RadiusAtomic Radius• Atomic radius: defined as ½ distance Atomic radius: defined as ½ distance

between neighboring nucleibetween neighboring nuclei in molecule or in molecule or crystalcrystal

• Affected byAffected by

1. # of energy 1. # of energy

levelslevels2. Proton Pulling2. Proton Pulling

PowerPower

http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH08/FG08_08.JPG

http://hmchemdemo.clt.binghamton.edu/zumdahl/docs/chemistry/07atomstructure/f0735.gif

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Increasing Atomic Radius

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Li: Group 1 Period 2 Cs: Group 1 Period 6Li: Group 1 Period 2 Cs: Group 1 Period 6

Cs has more energy levels, so it’s bigger

2-8NeVIIIA or 18

2-7FVIIA or 17

2-6OVIA or 16

2-5NVA or 15

2-4CIVA or 14

2-3BIIIA or 132-2BeIIA or 22-1LiIA or 1

ConfigurationElementFamily

As we go across, elements gain electrons, but they are getting smaller!

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Decreasing Atomic Radius


Why does this happen..Why does this happen..

• As you go from left to right, you again As you go from left to right, you again more protons (the atomic number more protons (the atomic number increases)increases)

• You have greater “proton pulling You have greater “proton pulling power” power” – Remember the nucleus is + and the electrons Remember the nucleus is + and the electrons

are - so they get pulled towards the nucleusare - so they get pulled towards the nucleus• The more protons your have, the more Proton The more protons your have, the more Proton

Pulling PowerPulling Power

as go across row size tends to decrease a as go across row size tends to decrease a bit because of greater PPP bit because of greater PPP ““proton pulling proton pulling powerpower””


We can “measure” the Proton We can “measure” the Proton Pulling Power by determining Pulling Power by determining the the EffectiveEffective nuclear chargenuclear charge

• It is the charge actually felt by valence It is the charge actually felt by valence electronselectrons

• The equationThe equation

Nuclear charge Nuclear charge -- # inner shell electrons # inner shell electrons

(doesn’t include valance e(doesn’t include valance e--))


Calculate Calculate ““effective nuclear chargeeffective nuclear charge””• # protons minus # inner electrons# protons minus # inner electrons

+7 +1

What the inner electrons do….

They Shield the charge felt by the valance electrons.


H and HeH and He: : only elements only elements whose whose valence valence electrons feel electrons feel full nuclear full nuclear charge (pull)charge (pull)

NOTHING NOTHING TO TO SHIELD SHIELD THEMTHEM

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Increased Electron Shielding

Look at all the shielding Francium's one valance electron has. It barely feels the proton pull from the nucleus. No wonder it will lose it’s one electron the

easiest. No wonder it’s the most reactive metal

Positive ions (Positive ions (cationscations))

• Formed by Formed by loss of electronsloss of electrons

• CationsCations always always smallersmaller than than parentparent atomatom

Ca

2e

8e

8e

2e

Ca+2

2e

8e

8e

Ca

Negative ions or (Negative ions or (anionsanions))

• Formed by Formed by gain of electronsgain of electrons

• AnionsAnions always always largerlarger than than parentparent atomatom

How do you know if an atom gains How do you know if an atom gains or loses electrons?or loses electrons?

• Think back to the Lewis structures of ionsThink back to the Lewis structures of ions

• Atoms form ions to get a valence of 8Atoms form ions to get a valence of 8

(or 2 for H)(or 2 for H)

• Metals tend to have 1, 2, or 3 valence electrons Metals tend to have 1, 2, or 3 valence electrons – ItIt’’s s easier to loseeasier to lose them them

• Nonmetals tend to have 5, 6, or 7 valence electronsNonmetals tend to have 5, 6, or 7 valence electrons– ItIt’’s s easier to addeasier to add some some

• Noble gases already have 8 so they donNoble gases already have 8 so they don’’t form ions t form ions very easilyvery easily

OR

Ionization EnergyIonization Energy

• = amount energy required to remove a = amount energy required to remove a valence electron from an atom in gas valence electron from an atom in gas phasephase

• 1st ionization energy = energy required to 1st ionization energy = energy required to remove the most loosely held valence remove the most loosely held valence electron (eelectron (e-- farthest from nucleus) farthest from nucleus)

•Cs valence electronCs valence electron lot lot farther away from nucleus than Li farther away from nucleus than Li •electrostaticelectrostatic attraction much weaker attraction much weaker so easier to steal so easier to steal electron away from Cselectron away from Cs•THEREFORE, Li has a higher Ionization energy then CsTHEREFORE, Li has a higher Ionization energy then Cs


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Decreased Ionization Energy (easier to remove an electron)

Increased Ionization Energy (harder to remove an electron)

ElectronegativityElectronegativity

• ability of atom to attract electrons in bondability of atom to attract electrons in bond

• noble gases tend not to form bonds, so noble gases tend not to form bonds, so dondon’’t have electronegativity valuest have electronegativity values

• Unit = Pauling Unit = Pauling • Fluorine: most electronegative Fluorine: most electronegative element element = 4.0 Paulings= 4.0 Paulings

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Increased Ionization Energy (harder to remove an electron)

Decreased Electronegativity

Increased Electronegativity

Reactivity of MetalsReactivity of Metals

• judge reactivity of metals by how easily judge reactivity of metals by how easily give up electronselectrons (they’re losers)

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Increased Ionization Energy (harder to remove an electron)D

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Most reactive metal = Fr(the most metallic)

More metallic

Reactivity of Non-metalsReactivity of Non-metals

• judge reactivity of non-metals by how judge reactivity of non-metals by how easily easily gain electrons (they are electrons (they are winners)winners)

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Increased Ionization Energy (harder to remove an electron)D

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Ele

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Most reactive metal = Fr(the most metallic)

More metallic

Most Reactive Nonmetal = F

Nonreactive

BACK

AllotropesAllotropes

• Different Different forms of element in same phaseforms of element in same phase

– different structures and propertiesdifferent structures and properties

• OO22 and O and O33 - both gas phase - both gas phase

–OO2 2 (oxygen) - necessary for life (oxygen) - necessary for life

–OO33 (ozone) - toxic to life (ozone) - toxic to life

• Graphite, diamond:Graphite, diamond:

–both carbon in solid formboth carbon in solid form

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Trends & the Periodic Table