Periodic Relationships Among the Elements

1
Periodic Relationships Among the Elements

• Chapter 8

2
Ground State Electron Configurations of the
Elements
8.2
3
Classification of the Elements
8.2
4
General Periodic Trends

• Atomic and ionic size
• Ionization energy
• Electronegativity
• Electron Affinity

5
Effective nuclear charge (Zeff) is the positive
charge felt by an electron.
Zeff Z - s
0 lt s lt Z (s shielding constant)
Zeff ? Z number of inner or core electrons
8.3
6
Effective Nuclear Charge (Zeff)
increasing Zeff
increasing Zeff
8.3
7
8.3
8
8.3
9
Atomic Radii
8.3
10
Atomic Size

• Size goes UP on going down a group.
• Because electrons are added further from the
  nucleus, there is less attraction. This is due to
  additional energy levels and the shielding
  effect. Each additional energy level shields
  the electrons from being pulled in toward the
  nucleus.

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Atomic Size

• Size decreases across a period owing to increase
  in the effective nuclear charge.

Small
Large
12
8.3
13
8.3
14
8.3
15
Ionization energy is the minimum energy (kJ/mol)
required to remove an electron from a gaseous
atom in its ground state.
I1 first ionization energy
I2 second ionization energy
Updated charges were left off left side of I2
and I3 earlier
I3 third ionization energy
I1 lt I2 lt I3
8.4
16
8.4
17
Filled n1 shell
Filled n2 shell
Filled n3 shell
Filled n4 shell
Filled n5 shell
8.4
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General Trend in First Ionization Energies
8.4
19
Electron affinity is the negative of the energy
change that occurs when an electron is accepted
by an atom in the gaseous state to form an anion.
DH -328 kJ/mol
EA 328 kJ/mol
DH -141 kJ/mol
EA 141 kJ/mol
8.5
20
8.5
21
8.5
22
Group 1A Elements (ns1, n ? 2)
8.6
23
Group 2A Elements (ns2, n ? 2)
8.6
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Group 7A Elements (ns2np5, n ? 2)
8.6
25
Group 8A Elements (ns2np6, n ? 2)
8.6
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Properties of Oxides Across a Period
8.6
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Electronegativity, ?

• ? is a measure of the ability of an atom in a
  molecule to attract electrons to itself.

Concept proposed by Linus Pauling 1901-1994
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Periodic Trends Electronegativity

• In a group Atoms with fewer energy levels can
  attract electrons better (less shielding). So,
  electronegativity increases UP a group of
  elements.
• In a period More protons, while the energy
  levels are the same, means atoms can better
  attract electrons. So, electronegativity
  increases RIGHT in a period of elements.

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Electronegativity