1
Molecular Shapes
Molecular Shapes
1. Areas of high electron density
repel each other
,
2. The e- domains arrange themselves as far apart
as possible on the central atom.
3. The molecule adopts whichever 3D geometry
minimized this repulsion
.
•
This controls the geometry around the central
atom
•
We call this
V
alence
S
hell
E
lectron
P
air
R
epulsion (
VSEPR
) theory.
Molecular Geometries: The VSEPR Model
Molecular Geometries: The VSEPR Model
There are 11 shapes that are important to us:
•
linear
(3 atoms, AB
2
);
bent
(3 atoms, AB
2
);
•
trigonal planar
(4 atoms, AB
3
);
trigonal
pyramidal
(4 atoms, AB
3
);
T-shaped
(4 atoms,
AB
3
);
•
tetrahedral
(5 atoms, AB
4
);
square planar
(5
atoms, AB
4
);
see-saw
(5 atoms, AB
4
);
•
trigonal bipyramidal
(6 atoms, AB
5
);
square
pyramidal
(6 atoms, AB
5
); and
•
octahedral
(7 atoms, AB
6
).
•When considering the geometry about the central
atom, we consider all electrons (lone pairs and
bonding pairs).
•
BUT
when naming the molecular geometry, we
focus only on the relative positions of the atoms.
Predicting Molecular Geometries
Predicting Molecular Geometries

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