Periodic Trends

Periodic Trends

1. Atomic Radius2. Ionization Energy3. Electronegativity4. Ionic Radius

0

50

100

150

200

250

0 5 10 15 20Atomic Number

Ato

mic

Ra

diu

s (

pm

)

Atomic Radius

Li

ArNe

KNa

• The distance from the center of the nucleus to the outermost valence shell

Atomic Radius

• Periodic Trend– Down a group the atomic radius increases

• Due to the added energy levels• Electron shielding: core e- block the attraction

between the nucleus and the valence e-

– Across a period it decreases

• Due to increased nuclear charge without additional shielding pulls e- in tighter

Ionization

• Atoms have no (or neutral) charges

• Ions are charged– Charge is caused by adding or losing

electrons• + charge: loss of electrons• - charge: gain of electrons

• Why does this occur?– Stability = full valence shell

© 1998 LOGAL

Ionization Energy

• Ionization Energy: the energy required to remove an electron from the valence shell– Why would an electron be removed?

• Periodic Trend (opposite atomic radii)– Down a group I.E. decreases

• Due to distance from nucleus & electron shielding

– Across a period it increases

• Due to increased nuclear charge without additional shielding pulls e- in tighter

• Removal of core electron = BIG IE• “Bumps” in graph due to loss of electrons

from stable electron configurations

0

500

1000

1500

2000

2500

0 5 10 15 20Atomic Number

1s

t Io

niz

ati

on

En

erg

y (k

J)

Ionization Energy

KNaLi

Ar

NeHe

Second and Third Ionization Energy

• Second I. E.: the energy required to pull the second electron off the same atom

• Third I.E.: the energy required to pull the third electron off the same atom

• Would the 2nd & 3rd IE be greater or lesser than the 1st?

Electronegativity

• Electronegativity: the ability of an atom to attract electrons in a chemical bond

• Periodic Trend– Down a group the electronegativity decreases

• Due to increasing atomic radii

– Across a period it increases• Due to decreased atomic radii

Ionic Radius

• The radius of a positive ion is smaller than the atomic radius of its neutral atom– Due to loss of electron and often energy level

Ionic Radius

• The radius of a negative ion is larger than the atomic radius of its neutral atom– Due to electron repulsion

© 2002 Prentice-Hall, Inc.

Examples

1. Which atom has the larger radii?• Be or Ba• Ca or Br

2. Which atom has the higher 1st I.E.?• N or Bi• Ba or Ne

3. Which particle has the larger radius?• S or S2-

• Al or Al3+