The solution: Valence bond theory
A
t
il
VSEPR
ith th
t
•
A way to reconcile VSEPR with the quantum
mechanical model for atomic orbitals
•
Appropriate s, p, and d orbitals on central
atom are mixed to create a new set of hybrid
orbitals directed towards bonded atoms and
lone pairs
•
Consider the bonding and geometry present in
CH
4
to illustrate this
S. Ensign, Chem. 1210
81

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109.5°
Bonding of C to H in methane, CH
4
C: Group 4A, 1s
2
2s
2
2p
2
, 4 bonds needed to satisfy octet
1s
2s
2p
Individual valence atomic orbitals of C in the ground state:
z
z
z
z
x
y
x
y
x
y
x
y
z
p
y
p
z
p
x
s
All four valence valence atomic
orbitals shown together:
x
y
S. Ensign, Chem. 1210
82

109.5°
Bonding of C to H in methane, CH
4
H 1
1
•H: 1s
•To get four bonds to H, electrons in the valence orbitals could be
1s
redistributed as follows:
•Note the bond angles that would result from overlap of atomic
bit l
ith th
1
bit l
f H
2s
2p
2s
2p
y
z
orbitals with the 1s orbitals of H:
y
z
H
y
z
H
90°
90°
x
x
C
C
+ 4
H
H
H
H
x
C
H
H
H
90
90°
S. Ensign, Chem. 1210
83
90