Molecular Geometries
Lewis dot structures are very useful in
determining the types of bonds in a molecule,
but they may not provide the best insight into
the spatial geometry of a molecule, i.e., how
the nuclei in a molecule are arranged in space.
The shape of molecules is very important in
determining how they might react with other
molecules.
Molecular Geometries
Remember that covalent bonds are formed
when electrons in atomic orbitals are shared
between two nuclei.
Methane H
ı
H–C–H
ı
H
1
,Molecular Geometries
The valence orbitals
available in carbon are the
2s and three 2p orbitals.
Hydrogen only has 1s
valence orbitals.
One approach to forming the
bonds would be to overlap
the 1s orbitals of H with the
2s and 2p orbitals of C.
What would be the results?
Molecular Geometries
When overlapping
the 1s orbitals of
H’s with the 2p
orbitals of carbon,
the bonds will be
separated by 90o H atom 1s
orbitals
in each direction
because the p
orbitals are
orthogonal.
2
, Molecular Geometries
H atom 1s
orbitals
When overlapping
the 1s orbital of H
with the 2s orbital
of carbon, the
bond will have no
specific orientation
in space because
both orbitals are
H atom 1s
spherical in shape. orbitals
Molecular Geometries
The result of this approach for CH4 would be a
molecule in which three of the bonds were orthogonal
to each other (separated by 90o) and the fourth bond
could point in any direction.
The true geometry of CH4 is tetrahedral—each C-H
bond is separated by 109.5o from the adjacent bonds.
3
Lewis dot structures are very useful in
determining the types of bonds in a molecule,
but they may not provide the best insight into
the spatial geometry of a molecule, i.e., how
the nuclei in a molecule are arranged in space.
The shape of molecules is very important in
determining how they might react with other
molecules.
Molecular Geometries
Remember that covalent bonds are formed
when electrons in atomic orbitals are shared
between two nuclei.
Methane H
ı
H–C–H
ı
H
1
,Molecular Geometries
The valence orbitals
available in carbon are the
2s and three 2p orbitals.
Hydrogen only has 1s
valence orbitals.
One approach to forming the
bonds would be to overlap
the 1s orbitals of H with the
2s and 2p orbitals of C.
What would be the results?
Molecular Geometries
When overlapping
the 1s orbitals of
H’s with the 2p
orbitals of carbon,
the bonds will be
separated by 90o H atom 1s
orbitals
in each direction
because the p
orbitals are
orthogonal.
2
, Molecular Geometries
H atom 1s
orbitals
When overlapping
the 1s orbital of H
with the 2s orbital
of carbon, the
bond will have no
specific orientation
in space because
both orbitals are
H atom 1s
spherical in shape. orbitals
Molecular Geometries
The result of this approach for CH4 would be a
molecule in which three of the bonds were orthogonal
to each other (separated by 90o) and the fourth bond
could point in any direction.
The true geometry of CH4 is tetrahedral—each C-H
bond is separated by 109.5o from the adjacent bonds.
3
