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Periodic Relationships
Among the Elements
Chapter 8
General Periodic Trends
•
•
•
•
Atomic and ionic size
Ionization energy
Electronegativity
Electron Affinity
Higher effective nuclear charge
Electrons held more tightly
Larger orbitals.
Electrons held less
tightly.
Shielding Effect!
Effective nuclear charge (Zeff) is the “positive charge” felt by an
electron.
Zeff  Z – number of inner or core electrons
Z
Core
Zeff
Radius
Na
11
10
1
186
Mg
12
10
2
160
Al
13
10
3
143
Si
14
10
4
132
8.3
Effective Nuclear Charge (Zeff)
increasing Zeff
increasing Zeff
8.3
8.3
8.3
Atomic Radii
8.3
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.
Atomic Size
Size decreases across a period owing to
increase in the effective nuclear charge.
Large
Small
Cation is always smaller than atom from which
it is formed.
Anion is always larger than atom from which it
is formed.
8.3
8.3
8.3
Ionization energy is the minimum energy (kJ/mol) required to
remove an electron from a gaseous atom in its ground state.
I1 + X (g)
X+(g) + e-
I1 first ionization energy
I2 + X+ (g)
X2+(g) + e-
I2 second ionization energy
I3 + X2+(g)
X3+(g) + e-
I3 third ionization energy
I1 < I2 < I3
8.4
8.4
Filled n=1 shell
Filled n=2 shell
Filled n=3 shell
Filled n=4 shell
Filled n=5 shell
8.4
Increasing First Ionization Energy
General Trend in First Ionization Energies
Increasing First Ionization Energy
8.4
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.
X (g) + e-
X-(g)
F (g) + e-
F-(g)
DH = -328 kJ/mol
EA = +328 kJ/mol
O (g) + e-
O-(g)
DH = -141 kJ/mol
EA = +141 kJ/mol
8.5
8.5
8.5
Group 1A Elements (ns1, n  2)
M+1 + 1e-
2M(s) + 2H2O(l)
4M(s) + O2(g)
2MOH(aq) + H2(g)
2M2O(s)
Increasing reactivity
M
8.6
Group 7A Elements (ns2np5, n  2)
X2(g) + H2(g)
X-1
2HX(g)
Increasing reactivity
X + 1e-
8.6
Group 8A Elements (ns2np6, n  2)
Completely filled ns and np subshells. Highest
ionization energy of all elements.
No tendency to accept extra electrons.
8.6
Properties of Oxides Across a Period
Less acidic
More acidic
Less basic
basic
acidic
More basic
8.6
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
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.
Electronegativity