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Title: Valence Bond Theory
Description: Introduction to how the hybridisation model can explain the shapes and bond lengths of various compounds, and a brief explanation of how to determine hybridisation. These notes are a part of my year 1 undergraduate degree in chemistry and were inspired by lectures with Dr Jason Lynam at the University of York.
Description: Introduction to how the hybridisation model can explain the shapes and bond lengths of various compounds, and a brief explanation of how to determine hybridisation. These notes are a part of my year 1 undergraduate degree in chemistry and were inspired by lectures with Dr Jason Lynam at the University of York.
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Valence Bond Theory
There are different ways of explaining how bonds are formed
...
Hybridization
Valence bond theory uses the idea of hybridization to explain bond length phenomena in
compounds such as CH4
...
Looking at the electronic configuration of
carbon shows 1s22s22p2, implying the 2s22p2 electrons are those involved in bonding
...
Sp3 Hybridization
Node
2p z
2p y
2p x
2s
For methane the 2s and 2p
orbitals are said to come
together to produce four new
sp3 hybridized orbitals
...
The C-H bonds are
formed by the overlap between
the sp3 orbitals of carbon, and
the 1s orbital of hydrogen
...
It is the shape that came first – the hybridization model is
just how we explain it!
Double Bonds
Hybridization can also explain the
shape that forms around
compounds with double bonds
...
This leads to a trigonal
2s
planar geometry about each of
3 x sp2 hybridzed
the carbon atoms
...
It’s these sp2 orbitals that are involved in the formation of the σ bonds in ethene
...
H
H
H
H
H
H
H
H
Triple Bonds
Again, this same model can be used to explain triple bonds! As before, hybrid orbitals are
used to form the σ framework
...
2 x sp hybridized orbitals
Hybridization and shape:
• If electron pair geometry (EPG) is linear – hybridization is sp
• If EPG is trigonal planar – hybridization is sp2
• If EPG is trigonal bipyramidal – hybridisation is sp3d
• If EPG is octahedral – hybridization is sp3d2
Hybridization and Bond Lengths
Hybridization shows a small affect on bond lengths, for example, the more s-character a bond
has, the shorter it will be
...
H3C
148 pm
CH3
153 pm
HC
H2C
HC
CH
C
C
CH
138 pm
CH2
Determining Hybridization
1
...
Calculate the number of bonds and lone pairs for the atom you’re looking at (double
and triple bonds count as one bond each)
3
Title: Valence Bond Theory
Description: Introduction to how the hybridisation model can explain the shapes and bond lengths of various compounds, and a brief explanation of how to determine hybridisation. These notes are a part of my year 1 undergraduate degree in chemistry and were inspired by lectures with Dr Jason Lynam at the University of York.
Description: Introduction to how the hybridisation model can explain the shapes and bond lengths of various compounds, and a brief explanation of how to determine hybridisation. These notes are a part of my year 1 undergraduate degree in chemistry and were inspired by lectures with Dr Jason Lynam at the University of York.