Lecture 4-6 January 27 –Feb. 3,
2016
Electrons in Atoms: Magnetism;
Term Symbols, Zeff, and Other
Properties
Gouy Balance for Magnetic Susceptibility
Three types of Magnetic Behavior
Paramagnetism: atoms, molecules, and solids with unpaired electrons are attracted
in a magnetic field—Decreases with increasing T.
Diamagnetic: substances with no unpaired electrons which are weakly repelled in a
magnetic field—no dependence on T.
Ferro-magnetism: the unpaired electons are aligned with their neighbors even in the
absence of a magnetic field
Magnetic domains: the groups of mutually aligned spins in a ferromagnetic substance
Ferro-magnet
In the absence
of a magnetic
field
Ferro-magnet
In the
presence of a
magnetic field
How do we approach magnetism?
Electron Assignments:
Identifying each and every
quantum number for each and
every electron:
n l ml ms
Electrons Characterized by
a) Principal energy level, n
b) Orbital or angular momentum, l = # of
angular nodes
c) Zeff
----------------------------------------------------------In the presence of a magnetic field of l is
oriented and composed of ml components.
d) Spin-spin and spin-orbital coupling
Box Diagrams
Figure 1.4 The possible sets of quantum numbers for n = 1 and n = 2.
ml values
Box Diagrams
Figure 1.5 The possible sets of quantum numbers for n = 3.
ml values
Ground State vs. Excited State Configurations
Term Symbols:
Spin:
2S + 1 L
J
S = Σ ms
= total spin angular
2S + 1 (called spin
momentum
“multiplicity”)
L = total orbital angular momentum
J=L + S
Term Symbols for Ground State
Electronic Configurations
• Pauli Exclusion Principle => Assignments to n and to l quantum
numbers. But there are other possibilities within assignment
• Hund’s Rule: Describes ground state only.
• Ground states will have
1st * Maximum value of S
2nd
* Maximum value of L within that S
Russell Saunders Coupling (L-S Coupling) for
Ground States
Configuration => Term Symbol
ΣmL = max. ML or L
ΣmS = MS or S
2S+1
2S+1
J
Spin
Multiplicity
# unpaired e-
S
2S+1
1
1/2
2
2
1
3
4
≈
L
State
⇒ doublet
0
⇒S
3
⇒ triplet
1
3/2
4
⇒ quartet
2
⇒P
⇒D
2
5
⇒ pentet
3
⇒F
4
⇒ G
Russell Saunders Coupling: Spin/Orbit Coupling
Inorganic Chemistry Chapter 1: Figure 1.22
© 2009 W.H. Freeman
Trends in Atomic Properties
• Size (atomic, ionic, covalent, van der Waals radii)
• Ionization Potential
(A0(g) + I.E.
• Electron Affinity Energies (A0(g) +
A+ + e- )
e-
A- + E.A.E.)
• Electronegativity: Ability of an atom, within a
molecule to attract electrons to itself.
Inorganic Chemistry Chapter 1: Figure 1.23
© 2009 W.H. Freeman
Van der Waal’s radii
1.22 Å /2 = 0.61Å
0.74 Å /2 = 0.37 Å
Inorganic Chemistry Chapter 1: Table 1.3
© 2009 W.H. Freeman
Inorganic Chemistry Chapter 1: Figure 1.24
© 2009 W.H. Freeman
Anions are Larger than
Neutral atom
Cations are smaller than
Neutral atom
Inorganic Chemistry Chapter 1: Table 1.4
© 2009 W.H. Freeman
Trends in Atomic Properties
• Size (atomic, ionic, covalent, van der Waals radii)
• Ionization Potential energy
(A0(g) + I.E.
A+ + e- )
• Electron Affinity Energy (A0(g) +
e-
A- + E.A.E.)
• Electronegativity: Ability of an atom, within a
molecule to attract electrons to itself.
Inorganic Chemistry Chapter 1: Figure 1.25
© 2009 W.H. Freeman
Ionization Energies give a clue
as to the types and formulae
of compounds that may be
formed, but they are not
the whole story.
ΔG = -nFE
Trends in Atomic Properties
• Size (atomic, ionic, covalent, van der Waals radii)
• Ionization Potential energy
(A0(g) + I.E.
A+ + e- )
• Electron Affinity Energy
(A0(g) +
e-
A-
+
E.A.E.)
• Electronegativity: Ability of an atom, within a
molecule to attract electrons to itself.
Copyright © 2014 Pearson
Education, Inc.
Inorganic Chemistry Chapter 1: Table 1.6
© 2009 W.H. Freeman
BDE:
427
436 kJ/mol
Electronegativity- Its Basis
• Pauling
• Mulliken
• Rochow
Linus Pauling
BDE H2 = 436 kJ/mol
BDE Cl2 = 239
BDE HCl = 427
Pauling: If strictly covalent: BDE HCl should be average of H2 and Cl2
Which would be ½ (436 + 239) = 338 kJ/mol. The extra stability
of ca. 100 kJ/mol is due to electronegativity difference,
and electrostatic attraction.
Inorganic Chemistry Chapter 1: Figure 1.27
© 2009 W.H. Freeman
Using Electronegativity Differences
to Predict types of Bonds:
Inorganic Chemistry Chapter 1: Figure 1.28
© 2009 W.H. Freeman