HF
H: 1s1
F: 1s22s22p5
Overlap between the valence orbital of H (1s) and valence
orbital of F (2p) to form a s bonds
Note: electron spin is paired in the s orbital
By definition: z is the direction along the internuclear axis
N2
N: 1s22s22p3
The two pz orbitals from each N can overlap to form a s
orbital.
The px and py orbitals are perpendicular to the internuclear
axis
s bond - overlap of
two pz orbitals
p bond - overlap of
two px orbitals and/or
two py orbitals
In a p bond, electron density has a nodal plane that contains
the bond axis
According to the VB theory
A single bond is a s-bond
A double bond is s-bond plus a p-bond
A triple bond is a s-bond and two p-bonds.
VB theory: assumes bonds form
when unpaired electrons in valence shell atomic orbitals pair
the atomic orbitals overlap end to end to form s-bonds or
side by side to form p-bonds.
Hybridization of Orbitals
C: Is2 2s2 2p2
VB theory, as described so far, would predict that C can form
just two bonds
In CH4, C forms four bonds.
C needs four unpaired electrons so that each can pair with a
H atom - need to revise valence-bond theory
“Promote” a 2s electron to a 2p orbital - this requires energy.
But now C has four unpaired electron and since bonding
releases energy the cost of promoting is overcome by the
lowering of energy on bond formation
H
CH4
C
H
H
H
Promoting a 2s electron to 2p allows C to have four unpaired
electrons.
All bonds on CH4 are equivalent
“Mix” the 2s and the three 2p orbitals to form four hybrid
orbitals all of the same energy and spatial distribution hybridization.
One s + three p = four sp3 orbitals
Hybrid orbitals are constructed on an atom to reproduce the
electron arrangement of the experimentally determined
shape of the molecule.
In CH4: each sp3 orbital has one unpaired electron
Each overlaps with a 1s orbital of H to form s-bond
The four resulting s-bonds point towards the corners of a
tetrahedron.
All four s-bonds are identical
http://www.whfreeman.com/chemicalprinciples/
Ethane: C2H6
Each C has four sp3 hybrid orbitals, pointing towards the
corner of a tetrahedron, each with one electron
Three of these four overlap with three H atoms forming sbonds (C sp3, H 1s).
The C-C bond is formed by an overlap of the remaining sp3
orbital on each C forming a s-bond (C sp3, C sp3).
NH3
N
H
H
H
H: Is1
N: Is2 2s2 2p3
Hybridize the 2s and 2p orbitals in N to form four sp3 hybrid
orbitals.
One of the sp3 has two paired electrons - the lone pair on N
The three other sp3 orbitals form s-orbitals with each of the
three H 1s orbitals
H2O
H
H: Is1
O
H
O: Is2 2s2 2p4
Hybridize the 2s and 2p orbitals in O to form four sp3 hybrid
orbitals.

O

2s




sp3
Two of the sp3 have two paired electrons - the two lone pairs
The two other sp3 orbitals overlap with H 1s orbitals
O


2p
An s orbital and two p orbitals can hybridize to form three
sp2 hybrid orbitals which point to the corners of an
equilateral triangle - trigonal planar geometry
Example: BF3
An s and a p orbital can hybridize into two sp orbitals that
point in opposite directions - linear geometry
PCl5 P: [Ne] 3s2 3p3

P

3p
Cl: [Ne] 3s2 3p5


Cl

3s

3p

_
_

3s
Promote a 3s electron to the 3d orbital
P



sp3d


_
_
empty 3d
Valence shell expansion - expansion to include d orbitals
along with s and p orbitals
One 2, three p, and one d orbital
form five sp3d hybrid orbitals, each
pointing towards a corner of a
trigonal bipyramid
One 2, three p, and two d
orbital form six sp3d2
hybrid orbitals, each
pointing towards a corner
of a octahedron
SF6
S: [Ne] 3s2 3p4
F: [He] 2s2 2p5

S


3p

3s
Include two 3d orbital and hybridize one s, three p and two d
S




sp3d2


_
_
_
empty 3d
Multiple Bonds
Ethylene: CH2CH2
Experimental data: all six atoms lie in the same plane and the
H-C-H and C-C-H bond angles are 120o.
Trigonal planar geometry indicates that each C is sp2
hybridized
For each C: two of the sp2
orbitals bond with two H 1s
orbitals to form s-bonds,
The third Csp2 bond on each
bond with each other to
form a C-C s-bond
The “pure” 2p orbitals on each C overlap to form a p-bond
between the two C atoms
The electron density of this p-orbital lies above and below the
axis of the C-C s-bond
http://www.whfreeman.com/chemicalprinciples/
Acetylene: C2H2
Linear molecule; each C is sp hybridized, leaving two pure p
orbitals on each C
http://www.whfreeman.com/chemicalprinciples/
Multiple bonds are formed when an atom forms a s-bond by
using an sp or sp2 hybrid orbital and one or more p-bonds
by using un-hybridized p orbitals
Formic acid: HCOOH