I II III

Unit 3: Electrons and the Periodic Table

Periodic Table Trends

Periodic Law

When elements are arranged in order of

increasing atomic #, elements with similar

properties appear at regular intervals.

0

50

100

150

200

250

0 5 10 15 20

Ato

mic

Ra

diu

s (p

m)

Atomic Number

What patterns

do you notice?

Atomic #s

3, 11, 19 are all

alkali metals

Atomic Radius size of atom

© 1998 LOGAL

Atomic Radius

Atomic Radius Average distance in an atom between the nucleus and the outermost electron

1

2

3

4 5

6

7

Atomic Radius Increases to the LEFT and DOWN

Atomic Radius

Fr

Smallest

biggest

Atomic Size Trend

Atomic Size increases down a group Why larger going down?

Adding more energy levels.

Atomic Size decreases across a period Why smaller across? Increased nuclear charge (more protons)

without additional energy levels pulls e- in closer.

Greater Coulombic Attraction

The closer you are to Francium, the larger you will

be!

Which is larger:

a.Rb or Li

Rb

b.N or Ne

N

Atomic Size & Radius Examples

Ionization Energy

Ionization energy is the amount of energy needed to remove an electron.

M + energy M+1 + e-

Electrons that are close to the nucleus are hard to remove because they are under a strong force of attraction

Ionization Energy Trend

Ionization Energy Increases across a period Why? Valence electrons experience a greater

nuclear force because they are closer to the nucleus.

Smaller atoms have higher Ionization energy.

Ionization Energy Decreases down a group. Why? Valence electrons removed are farther

from the nucleus because they are in higher energy levels.

Bigger atoms have lower Ionization energy.

Why opposite of atomic radius?

In small atoms, e- are close to the nucleus where the attraction is stronger

Small atoms have High IE

Big Atoms have Low IE

Ionization Energy Trends

Lowest as you go DOWN and to the LEFT

Ionization Energy

1

2

3

4 5

6

7

Fr

Bottom left elements (Metals) WANT to lose an electron to become more stable.

High IE

Low IE

Which would have a higher Ionization energy, Sodium or Chlorine?

Chlorine has higher IE.

Chlorine is smaller and has a higher nuclear charge (more protons) = stronger hold on electron = higher energy to take it away.

Also, remember – Na wants to lose an electron (it is a metal) and Cl wants to gain an electron (non-metal)

First Ionization Energy

0

500

1000

1500

2000

2500

0 5 10 15 20Atomic Number

1s

t Io

niz

ati

on

En

erg

y (k

J)

E. Ionization Energy

KNaLi

Ar

NeHe

Successive Ionization Energies

Mg 1st I.E. 736 kJ

2nd I.E. 1,445 kJ

Core e- 3rd I.E. 7,730 kJ

Large jump in I.E. occurs when a CORE e- is removed.

Ionization Energy

Al 1st I.E. 577 kJ

2nd I.E. 1,815 kJ

3rd I.E. 2,740 kJ

Core e- 4th I.E. 11,600 kJ

Successive Ionization Energies

Large jump in I.E. occurs when a CORE e- is removed.

Ionization Energy

Electronegativity

The ability of an atom to attract an electron.

The smaller the atom, the more electronegative it is because of a greater nuclear force.

Electronegativity Trends

Electronegativity Increases across a period. Why? Non-metals such as F, O and N want

more electrons to complete their valence shell.

Smaller atoms have greater nuclear charge and thus, more force to attract electrons.

Exception: Noble gases are not included because they generally do not want to gain electrons. They are already stable.

Electronegativity Trends

Electronegativity Decreases Down a Group Why? Atomic size increases and valence

electrons are farther from the nucleus. More energy levels increases shielding. So

the pull from the positive nuclear charge is less.

In General: Non-Metals have high ElectronegativitiesMetals have low Electronegativities

Highest as you go UP and to the RIGHT towards Fluorine

Electronegativity Trends

1

2

3

4 5

6

7

F

Remember- Noble gases not included in this trend!

Ionic Radius Cations (+ ions) the ionic radius is smaller than the original atom.

Why? There is an increased attraction for the fewer electrons that remain.

Ionic Radius

Na Na+

Ionic Radius

For Anions (– ions) the ionic radius is

larger than the original atom.

Why? The nuclear attraction is less for

an increased number of electrons.

Extra electrons repel each other and

spread out – larger!)

© 2002 Prentice-Hall, Inc.

Cl Cl-1

Practice

Which atom is larger H or He?

Which atom has a greater ionization energy, Ca or Sr?

Which atom is more electronegative, F or Cl?

Hydrogen – Smaller nuclear charge

Ca – smaller, less shielding, lower effective nuclear charge

Fluorine – Smaller, less shielding with less

energy levels, so easier to attract electron

Which atom has the larger radius?

Be or Ba

Ca or Br

Ba –more energy levels

Ca – lower nuclear charge

Examples

Which atom has the higher 1st I.E.?

N or Bi

Ba or Ne

N

Ne

Examples

Which particle has the larger radius?

S or S2-

Al or Al3+

S2-

Al

Examples

Alkali Metal Reactivity