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AX5
sp3d hybridiza0on
Require 5 unpaired electrons
3s2 3p3
What about 3d orbital?
AX5 sp3d hybridiza0on
5 domains therefore trigonal bipyramidal
Domains, hybrids, and geometry correspondence
domain hybridiza0on geometry 2 sp linear 3 sp2 trigonal planar 4 sp3 tetrahedral 5 sp3d trigonal bipyramidal 6 sp3d2 octahedral
domains hybridiza0on
Molecule Domain arrangement hybridiza5on
BF3 PF5
XeOF4 H3O+
CH4
ClO-‐2
CO2
SF6 BeCl2
trigonal planar sp2
trigonal bipyramidal sp3d
tetrahedral sp3
linear
octahedral sp3d2
sp
octahedral sp3d2
tetrahedral sp3
trigonal planar sp2
linear sp
5
Orbitals in molecules
We have seen that two atomic orbitals form a bond when they overlap.
While the electrons in the bond are more likely to be found in the overlap region
they are not confined to this region.
They have a high probability of being anywhere within the contours of the overlapping atomic orbitals.
Lecture notes 24
6
This gives rise to the concept of a molecular orbital,
i.e. an orbital that belongs to the en0re molecule
with the overlap region serving as a gateway
that allows the electrons from one atom in the bond
to mix with those from the other atom.
7
This gives rise to the concept of a molecular orbital, i.e. an orbital that belongs to the en0re molecule with the overlap region serving as a gateway
that allows the electrons from one atom in the bond To mix with those from the other atom.
Valence bond Molecular orbital
8
+
+
+
_
_
_
+
Orbitals have algebraic signs
9
Bond between two s orbitals
σ bonds
+
Bond between an s and a p orbital
+
Bond between two p orbitals
+ +
+ +
+ + _
_ _ +
10
σ orbitals
Cylindrically symmetric
View down bond axis View from the side
p on A and p on B π bonds
+ + + +
_ _ _ _
Reinforce Form π bond
Internuclear line
Internuclear axis Possible p orbitals Z X or Y X Z or Y
X or Z Y
p on A and p on B π bonds
+ + + +
_ _ _ _ _
+ posiGve
negaGve
y px & d xy or pz & dzy
+
+
+
_ _
_
Internuclear line bonding combina0ons
z px & dxz or py & dyz
x py & dxy or pz & dzx
Reinforce form π bond
d – p π bonds
π bonds
+
_
posiGve
negaGve
Down axis view
_
+
View from side
s on A and p on B possible overlaps
Internuclear line
+
+
+
+
+
+ +
+ _
_
_ _
Reinforce form bond
cancel no bond
+
+
+
_
_
Cancel no bond
s and d
p on A and p on B possible overlaps
+ +
+ +
+
+ +
+ _ _
_
_
_ _
_
_
Reinforce Form σ bond
Cancel no bond
Internuclear line
y py d xy & dzy
+
+
+ _
_
_
Internuclear line p orbital d orbitals
z pz dxz & dyz
x px d yx & dzx
Cancel no bond
19
MulGple Bonding
NO3−Nitrate ion
Domains ? 5 + 3x6 +1 = 24 Valence electrons ?
24/8 = 3 +R(0) Trigonal planar
O
N
O O
O
N
O O
: :
:
sp2 hybrids
20
MulGple Bonding NO3−
N
O
O O
Electrons delocalize into all atomic pπ orbitals
21
MulGple Bonding NO3−
N
O
O O
Electrons delocalize into all atomic pπ orbitals
22
:N ≡ N :1 σ and 2 π bonds
O = C =O
1 σ and 1 π bond
H −C ≡ C − H1 σ bond 1 σ and 2 π bonds
23
Some combina0on of orbitals cannot form a bond because they have zero overlap
Can form a bond
A B z axis
A B s s pz s s pz pz pz
A B s px,py px,py s px pz,py pz,py px py pz,px pz,px py pz px,py px,py pz
Cannot form a bond
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