2.4 Methane Molecule, as Example of Pentatomic
Molecule
T d symmetry guaranties the highest stability for the CH 4 unit due to the energy
decrease of b 1g eigenfunction (Scheme 2.8).
2.5 Considerations About the Models of Chemical Bond
in Use Before the Adoption of the Symmetry
Molecular Orbital Model
In the time before the introduction of the molecular orbital model, two different
models were proposed to rationalize the molecular shape, the reactivity, and the
electronic configuration of a molecule. (1) the primitive Lewis model that does not
Orbital
a
)
C
(
s
2
1
2a 1
2p
2s
E
C
T d
D 4h
4H
1s
2a 1g
1a 2u
1a 1
1t 2
1a 1g
1e u
1b 1g
a 1g
a 1g
a 2u
b 1g
e u
2e u
e u
a 1
T d
D 4h
t 2
2t 2
t 2
+
+ +
2p x (C)
2p y (C)
2p z (C)
4x1s(H)
Point group
Scheme 2.8 Energy level trend of methane symmetry orbitals
36
2 Symmetry Orbitals for Different Bis and Polyatomic Molecules