Orbital Hybridization

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Orbital Hybridization

• Edward A. Mottel
• Department of Chemistry
• Rose-Hulman Institute of Technology

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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
The shape is determined by the linear
combinations of atomic orbitals
y2s y2pz
y2s - y2pz
and
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sp2 Orbital Hybridization
The 2s 2px and 2pz atomic orbitals of each
carbon are used.

2pz
2px
2s
sp2
The angle between the orbitals is 120.
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sp3 Orbital Hybridization
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sp3 Orbital Hybridization
The angle between the orbitals is 109.5.
Why isnt the angle 90
four sp3 orbitals
tetrahedral shape
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Predict the bond angles and the hybridization of
the central atoms in each of the following
structures.
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Predict the bond angles and the hybridization of
the central atoms in each of the following
structures.
sp Be
sp3 N
sp3 O
sp2 C
sp2 N
sp3 C
sp C
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Beryllium sp Hybridization
Two orbitals each can hold two electrons
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sp Hybridization
px py
Maximum angle that two orbitals can be apart is
180.
hao
atomic orbtials
hybrid atomic orbtials
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sp Hybridized BerylliumValence Orbitals
The other p-orbitals of beryllium (px py) remain
unchanged
Open orbital contains no electrons Lined orbital
contains one electron Filled in orbital contains
two electrons
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sp Hybridized BerylliumValence Orbitals
The other p-orbitals of beryllium (px py) remain
unchanged
Why is it a linear molecule
Open orbital contains no electrons 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
sp3 N
sp3 O
sp2 O
sp2 C
sp2 N
sp N
sp3 C
sp C
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Sketch the hybrid atomic orbitals and fill
or shade-in the lobes for each indicated atom
sp2 O
sp3 O
sp3 N
sp2 C
sp2 N
sp C
sp N
sp3 C
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Ethene

• Also called ethylene
• Polymerizes to form polyethylene
• Each carbon forms three sp2 hybrid orbitals.

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

• 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
carbon-hydrogen sigma bonds due to sp2-s overlap
carbon-carbon pi bond due to 2py- 2py overlap
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Methane
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
sp3
All four hybrid atomic orbitals have the
same energy.
These four orbitals are energetically degenerate.
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Methane
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Ammonia
N
H
H
H
The 2s 2px 2py and 2pz atomic orbitals of
nitrogen are used
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sp3 Hybridization
sp3
By hybridizing its atomic orbitals nitrogen
gains more stable (lower energy) orbitals for
bonding.
hao
nitrogen ao
Which of the electrons in these hybrid atomic
orbitals are available for bonding
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Ammonia
a completely filled in orbital contains two
electrons
Because of this bonding the Ð H-N-H bond
angle is close to 109.5 (actually 107).
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The Structure of Ammonia
What bond angle would be expected if the lone
pair of electrons didnt 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
2 groups of electrons around carbon
What does the orbital overlap diagram look like
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Hydrogen Cyanide
carbon sp hybridized
nitrogen sp hybridized
hydrogen 1s orbital
How many electrons are in each orbital
How many electrons are in each orbital
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Hydrogen Cyanide
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Hydrogen Cyanide
(between carbon and nitrogen)
(between hydrogen and carbon and carbon and
nitrogen)
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Nitrite Ion
Why is the bond angle approximately 120
3 groups of electrons around nitrogen
Ð O-N-O _at_ 120
Draw the hybridized atomic orbitals for each atom
O1 sp2 hybridized O2 sp3 hybridized
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Nitrite Ion
-1 charge
1s2 2s2 2p4
1s2 2s2 2p3
1s2 2s2 2p4
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Nitrite Ion
What other kind of bond is formed
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Nitrite Ion
N
O
O
Where is the pi bond located
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Nitrite Ion
How would the bonding change if O2 was
unhybridized
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Nitrite Ion
-1 charge
1s2 2s2 2p4
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Nitrite Ion
What other kind of bond is formed
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Nitrite Ion
pi bond formation
How could resonance in this molecule be
explained
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Ethene
3 groups of electrons around carbon
Ð C-C-H _at_ 120 Ð H-C-H _at_ 120
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Ethene
How many sigma bonds and how many pi bonds are
formed
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Ethane
4 groups of electrons around carbon
Ð C-C-H _at_ 109.5 Ð H-C-H _at_ 109.5
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Ethane
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.
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

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Electronegativity
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