Orbital Hybridization
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
Atomic Orbitals & Covalent Bonding
Atomic orbitals are mathematical descriptions
of the probable locations of electrons around
an atom.
s, px, py, pz, dxy, dxz, dyz, dx2-y2, dz2, ...
Atomic orbitals can be “blended” together
to form new orbitals called hybrid orbitals.
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sp Orbital Hybridization
Be
Be
Be
Be
The shape is determined
by the linear combinations
of atomic orbitals
y2s + y2pz
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and
y2s - y2pz
Be
sp2 Orbital Hybridization
The 2s, 2px and 2pz atomic orbitals
of each carbon are used.
C
2s
+ C +
2px
C
2pz
=
sp2
The angle between the orbitals is 120°.
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sp3 Orbital Hybridization
x
+
2s
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+
2px
y
z
+
2pz
2py
sp3 Orbital Hybridization
The angle between the orbitals is 109.5°.
Why isn’t the angle 90°?
four sp3 orbitals
tetrahedral shape
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Groups
of
Hybridization
Electrons
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Ideal
Bond
Angle
2
sp
180º
3
sp2
120º
4
sp3
109.5º
Predict the bond angles and the hybridization
of the central atoms
in each of the following structures.
H •• Be ••
H
H
N
C O
••
H
H
••
H •• O •• N
O
••
••
H
H •• C •• C •• •• •• N ••
H
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Predict the bond angles and the hybridization
of the central atoms
in each of the following structures.
sp Be
3 N
sp
H
•
•
H • Be • H
N
H
sp3 O
••
sp2 C
H
••
H •• O •• N sp2 N
O
••
••
H
H •• C •• C •• •• •• N ••
sp3 C H sp C
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C O
Beryllium sp Hybridization
Be
Be
Be
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and
Be
Two orbitals
each can hold two electrons
sp Hybridization
2p
energy
px, py
sp
2s
ao
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atomic
orbtials
hao
Be
Maximum angle that
two orbitals can be
apart is 180°.
hybrid atomic
orbtials
sp Hybridized Beryllium
Valence Orbitals
The other p-orbitals
of beryllium (px, py)
remain unchanged
x
y
Be
Open orbital contains no electrons
Lined orbital contains one electron
Filled in orbital contains two electrons
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z
sp Hybridized Beryllium
Valence Orbitals
The other p-orbitals
of beryllium (px, py)
remain unchanged
H
Why is it a linear molecule?
Be
Open orbital contains no electrons
Lined orbital contains one electron
Filled in orbital contains two electrons
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H
two sigma
bonds
H
Be
H
Sketch the hybrid atomic orbitals and fill or
shade-in the lobes for each indicated atom
sp3 N
H
N
H
sp3 O
••
sp2 C
H
••
H •• O •• N sp2 N
O
C O sp2 O
••
••
H
H •• C •• C •• •• •• N •• sp N
sp3 C H sp C
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Sketch the hybrid atomic orbitals and fill or
shade-in the lobes for each indicated atom
sp3 O
sp2 C
sp3 N
sp2 O
sp2 N
sp3 C
sp C
sp N
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Ethene
C •• •• C
H
H
 Also
called ethylene
 Polymerizes to form polyethylene
 Each carbon forms three sp2 hybrid orbitals.
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sp2 Hybridization
energy
2py
sp2
2s
ao
hao
The unhybridized py orbital is
perpendicular to the sp2 orbitals.
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This hybrid set
can hold six electrons.
Ethene
Top down view
(xz plane)
y
Edge on view
To allow for overlap of the unhybridized py
orbitals, the bonding in this molecule requires
that ethene is planar. All six atoms lie in the
same plane.
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Ethene
carbon-carbon sigma bond
due to sp2-sp2 overlap
H
H
C
H
carbon-carbon pi bond
due to 2py- 2py overlap
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C
H
carbon-hydrogen
sigma bonds
due to sp2-s overlap
Methane
••
••
H
H •• C •• H
H
The 2s, 2px , 2py and 2pz atomic orbitals
of carbon are used.
What would be the name of a hybrid orbital
made from these orbitals?
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sp3 Hybridization
2p
energy
sp3
All four hybrid
atomic orbitals
have the same
energy.
2s
carbon
ao
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hao
These four orbitals are
energetically degenerate.
Methane
H
carbon-hydrogen
sigma bonds
due to sp3-s overlap
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H C
H
H
••
Ammonia
••
H •• N •• H
H
The 2s, 2px , 2py and 2pz atomic orbitals of nitrogen
are used
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sp3 Hybridization
2p
energy
sp3
2s
nitrogen
ao
hao
By hybridizing its
atomic orbitals
nitrogen gains
more stable
(lower energy)
orbitals for bonding.
Which of the electrons in these
hybrid atomic orbitals are available for bonding?
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Ammonia
Because of this bonding,
the  H-N-H bond angle
is close to 109.5° (actually 107°).
••
a completely filled in
orbital contains
two electrons
nitrogen-hydrogen
sigma bonds
due to sp3-s overlap
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H N
H
H
The Structure of Ammonia
What bond angle would be expected if the
lone pair of electrons didn't affect the structure?
What bond angle would be expected if the
atomic orbitals of nitrogen did not hybridize?
Why is the actual bond angle not exactly 109.5°?
Draw the orbital overlap diagram for the reaction
of ammonia and a hydrogen ion.
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Hydrogen Cyanide
H C N
H •• C •• •• •• N ••
What does the orbital
overlap diagram look like?
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2 groups of electrons
around carbon
sp hybridization
 H-C-N = 180°
Hydrogen Cyanide
H •• C •• •• •• N ••
hydrogen
1s orbital
carbon
sp hybridized
nitrogen
sp hybridized
How many electrons How many electrons
are in each orbital? are in each orbital?
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Hydrogen Cyanide
H •• C •• •• •• N ••
sigma bonds
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px orbital
overlap
py orbital
overlap
Hydrogen Cyanide
H •• C •• •• •• N ••
sigma bonds
(between hydrogen and carbon
and carbon and nitrogen)
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2 pi bonds
(between carbon
and nitrogen)
Nitrite Ion
Why is the bond angle
approximately 120°? O N O
•
O
N
O
3 groups of electrons
around nitrogen
sp2 hybridization
 O-N-O @ 120°
Draw the hybridized
atomic orbitals
O1 sp2 hybridized
for each atom
O2 sp3 hybridized
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•
Nitrite Ion
O
N
O
-1 charge
1s2 2s2 2p4
_ ___ _
1s sp2 p
1s2 2s2 2p3
1s2 2s2 2p4
_ ___ _
1s sp2 p
_ ____
1s
sp3
•
Nitrite Ion
O
N
O
What other kind of bond is formed?
Nitrite Ion
•
O
N
O
O
N
O
Where is the pi bond located?
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Nitrite Ion
O N O
•
O
N
O
3 groups of electrons
around nitrogen
sp2 hybridization
 O-N-O @ 120°
How would the bonding change
if O2 was unhybridized?
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•
Nitrite Ion
O
N
O
-1 charge
1s2 2s2 2p4
_ ___ _
1s sp2 p
1s2 2s2 2p3
1s2 2s2 2p4
_ ___ _
1s sp2 p
_ _ ___
1s 2s 2p
•
Nitrite Ion
O
N
O
What other kind of bond is formed?
Nitrite Ion
•
O
N
O
pi bond formation
How could resonance in this molecule be explained?
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Ethene
H H
C C
H H
C •• •• C
H
H
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3 groups of electrons
around carbon
sp2 hybridization
 C-C-H @ 120°
 H-C-H @ 120°
Ethene
C •• •• C
H
H
How many sigma bonds and
how many pi bonds are formed?
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Ethane
H H
H C C H
H H
••
••
••
••
H H
H •• C •• C •• H
H H
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4 groups of electrons
around carbon
sp3 hybridization
 C-C-H @ 109.5°
 H-C-H @ 109.5°
Ethane
••
•
•
••
•
•
H H
H •• C •• C •• H
H H
What kind of bonds are formed?
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Dipole Moments
 Charge
is not always equally distributed in a
molecule.
 There
can be a region of positive charge and
of negative charge.
 The vector connecting these regions is called
the dipole moment.
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Predictions
 For
molecular compounds
• solubility and miscibility are related to the
polarity (i.e., dipole moment) of the molecule.
 "Like
dissolves like" is a rule of thumb for solubility
• polar molecules dissolve in polar solvents
• nonpolar molecules dissolve in nonpolar solvents
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Carbonate Ion
The concept of dipole moments
can also be applied to ions,
although they generally
dissolve in polar solvents
(e.g., water) because
of their charge.
O 2O
C
O
Although carbonate ion
has no net dipole moment,
it dissolves in polar solvents
because of its ionic charge.
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Like Dissolves Like
 The
rule "like dissolves like" is not perfect;
 However, it does serve as a starting point in
determining what type of solvent to use when
attempting to dissolve a solid.
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Polarity Predictions
 Rank
the following molecules in terms of
polarity:
• water, benzene, chloroform
••
••
H
O
H
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H
Cl
C
Cl
Cl
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Electronegativity
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