Periodic Trends

November 18November 18thth & 19 & 19thth, , 20092009

Periodic Periodic TrendsTrends

Periodic LawPeriodic Law

When elements are arranged in When elements are arranged in

order of increasing atomic #, order of increasing atomic #,

elements with similar properties elements with similar properties

appear at regular intervals appear at regular intervals

(periodically).(periodically).

Periodic PropertiesPeriodic Properties

© 1998 LOGAL

Atomic Radius

Size of atom

First Ionization Energy

Energy required to remove one e- from a neutral atom.

© 1998 LOGAL

Electronegativity

How much an atom pulls

Electrons towards itself in a bond

Atomic RadiusAtomic Radius

Size of atomSize of atom

0

50

100

150

200

250

0 5 10 15 20Atomic Number

Atomic Radius (pm)

Li

ArNe

KNa

1

2

3

4 5

6

7

Atomic RadiusAtomic Radius

Increases to the LEFT and DOWN Francium is the largest atom

Atomic RadiusAtomic RadiusWhy larger going down?Why larger going down?

Higher energy levels have larger orbitalsHigher energy levels have larger orbitals

Why smaller to the right? Why smaller to the right?

ShieldingShielding – core electrons block the – core electrons block the attraction between the nucleus and the attraction between the nucleus and the valence electronsvalence electrons

Increased nuclear charge without additional Increased nuclear charge without additional shielding pulls electrons in tightershielding pulls electrons in tighter

Ionization EnergyIonization EnergyEnergy required to remove an electronEnergy required to remove an electron

It ALWAYS requires some energy to remove an electron!!It ALWAYS requires some energy to remove an electron!!

0

500

1000

1500

2000

2500

0 5 10 15 20Atomic Number

1st Ionization Energy (kJ)

KNaLi

Ar

NeHe

1

2

3

4 5

6

7

Ionization EnergyIonization Energy

Increases UP and to the RIGHT Helium has the highest Ionization Energy

Ionization EnergyIonization EnergyWhy opposite of atomic radius?Why opposite of atomic radius?

In small atoms, eIn small atoms, e-- are close to the nucleus where the attraction is stronger and they are harder to pull off are close to the nucleus where the attraction is stronger and they are harder to pull off

Small atom = high ionization energySmall atom = high ionization energy

In larger atoms, the valence electrons are easier to pull offIn larger atoms, the valence electrons are easier to pull off

Large atom = low ionization energyLarge atom = low ionization energy

ElectronegativityElectronegativityAbility of an atom to pull Ability of an atom to pull

electrons towards itself in a bond.electrons towards itself in a bond.

1

2

3

4 5

6

7

Increases UP and to the RIGHT Fluorine has the highest electronegativity Noble gases have no electronegativity

because they don’t form bonds

Electronegativity

Why opposite of atomic radius?

In small atoms, there is less shielding so

the protons pull harder on electrons

Small atom = high electronegativity

In larger atoms, there is more shielding

Large atom = low electronegativity

ElectronegativityElectronegativity

ExamplesExamples

Which atom has the larger radius?Which atom has the larger radius?

Be or Ba

Ca or Br

Ba

Ca

ExamplesExamples

Which atom has the higher Ionization Energy?Which atom has the higher Ionization Energy?

N or Bi

Ba or Ne

N

Ne

ExamplesExamples

Which atom has the higher electronegativity?Which atom has the higher electronegativity?

Li or C

Cr or Kr

C

Kr?