# Orbital Hybridization

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```					    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

The shape is determined
Be       by the linear combinations     Be
of atomic orbitals
y2s + y2pz    and    y2s - y2pz

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sp2 Orbital Hybridization
The 2s, 2px and 2pz atomic orbitals
of each carbon are used.

C       + C +         C        =

2s             2px    2pz                  sp2
The angle between the orbitals is 120°.

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sp3 Orbital Hybridization
x
y
+    +          +                 z

2s            2px   2pz              2py

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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                   Ideal
of    Hybridization   Bond
Electrons                 Angle
2           sp         180º
3           sp2        120º
4           sp3        109.5º

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Predict the bond angles and the hybridization
of the central atoms
in each of the following structures.

H
H • Be •
•    •   H
N
H          C O
•
•

H•O • N
• •                                 H
•
•

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
•    •              H     sp3 N
H • Be • H
N
sp3 O                              H         C O
sp2 C
•
•

H • O • N sp2 N
• •                                   H
•
•

O             H
•
•
H • C • C •• • N •
• • ••• •
•
•

sp3 C H sp C
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Beryllium sp Hybridization

Be

Be     and      Be

Be              Two orbitals
each can hold two electrons

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sp Hybridization

2p                       px, py
energy

sp               Be

Maximum angle that
2s                            two orbitals can be
ao    hao            apart is 180°.

atomic    hybrid atomic
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sp Hybridized Beryllium
Valence Orbitals
The other p-orbitals
of beryllium (px, py)                 x
remain unchanged
y
Be     z

Open orbital contains no electrons
Lined orbital contains one electron
Filled in orbital contains two electrons

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sp Hybridized Beryllium
Valence Orbitals
The other p-orbitals
Why is it a linear molecule?
of beryllium (px, py)
remain unchanged

H       Be     H      two sigma
bonds
Open orbital contains no electrons              H    Be    H
Lined orbital contains one electron
Filled in orbital contains two electrons

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Sketch the hybrid atomic orbitals and fill or
shade-in the lobes for each indicated atom

H       sp3 N
N
sp3 O                          H         C O sp2 O
sp2 C
•
•

H • O • N sp2 N
• •                               H
•
•

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
2py
energy

sp2

2s
ao      hao        This hybrid set
can hold six electrons.
The unhybridized py orbital is
perpendicular to the sp2 orbitals.

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Ethene         y

Top down view                 Edge on view
(xz plane)

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   C
H            H
carbon-hydrogen
carbon-carbon pi bond                     sigma bonds
due to 2py- 2py overlap               due to sp2-s overlap

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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

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sp3 Hybridization
2p
sp3
energy

All four hybrid
atomic orbitals
have the same
2s                        energy.
carbon   hao
ao          These four orbitals are
energetically degenerate.

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Methane

H

H C
H  H
carbon-hydrogen
sigma bonds
due to sp3-s overlap

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Ammonia

•
•
H • N• H
• •

•
•
H

The 2s, 2px , 2py and 2pz atomic orbitals of nitrogen
are used

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sp3 Hybridization
2p
sp3
energy

By hybridizing its
atomic orbitals
2s                              nitrogen gains
more stable
nitrogen    hao           (lower energy)
ao              orbitals for bonding.

Which of the electrons in these
hybrid atomic orbitals are available for bonding?
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a completely filled in   Ammonia
orbital contains
two electrons               Because of this bonding,
the  H-N-H bond angle
is close to 109.5° (actually 107°).

•
•
H N
H  H
nitrogen-hydrogen
sigma bonds
due to sp3-s overlap

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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

2 groups of electrons
H • C •• • N •
• ••• •             around carbon

sp hybridization
 H-C-N = 180°
What does the orbital
overlap diagram look like?

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Hydrogen Cyanide
H • C •• • N •
• •• • •

hydrogen            carbon               nitrogen
1s orbital       sp hybridized        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
px orbital
overlap

py orbital
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Hydrogen Cyanide
H • C •• • N •
• •• • •

sigma bonds                    2 pi bonds
(between hydrogen and carbon    (between carbon
and carbon and nitrogen)       and nitrogen)

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Nitrite Ion
Why is the bond angle
approximately 120°? O N O

3 groups of electrons
•

N               around nitrogen
O       O
sp2 hybridization
Draw the hybridized           O-N-O @ 120°
atomic orbitals
O1 sp2 hybridized
for each atom  O2 sp3 hybridized
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Nitrite Ion
•
N
O       O

-1 charge

1s2 2s2 2p4   1s2 2s2 2p3   1s2 2s2 2p4

_ ___ _        _ ___ _       _ ____
1s sp2 p       1s sp2 p      1s sp3
Nitrite Ion
•
N
O       O

What other kind of bond is formed?
•                  Nitrite Ion
N
O          O

N        O
O

Where is the pi bond located?

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Nitrite Ion

O N O

3 groups of electrons
•

N                 around nitrogen
O       O
sp2 hybridization
 O-N-O @ 120°

How would the bonding change
if O2 was unhybridized?
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Nitrite Ion
•
N
O       O

-1 charge

1s2 2s2 2p4   1s2 2s2 2p3   1s2 2s2 2p4

_ ___ _        _ ___ _       _ _ ___
1s sp2 p       1s sp2 p      1s 2s 2p
Nitrite Ion
•
N
O       O

What other kind of bond is formed?
•            Nitrite Ion
N
O          O

pi bond formation
How could resonance in this molecule be explained?
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Ethene
H H
C C
H H
3 groups of electrons
around carbon
C• • C
••
sp2 hybridization
H      H
 C-C-H @ 120°
 H-C-H @ 120°

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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
4 groups of electrons
H H           around carbon
•
•  •
•

H • C•C • H
• • •             sp3 hybridization
 C-C-H @ 109.5°
•
•  •
•

H H
 H-C-H @ 109.5°

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H H             Ethane
•
•      •
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,                   O 2-
although they generally
O     C
dissolve in polar solvents
(e.g., water) because                          O
of their charge.
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               C
H           H     Cl        Cl
Cl

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Electronegativity

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