Periodic Trends
Jan 21, 2016
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+