Chapter 9: Molecular Geometry
and Bonding Theories
What do the molecules look like and why?
Valence Shell Electron Pair
Repulsion Theory (VSEPR)
• VESPR is a model of how molecules arrange
themselves and get their shape.
• It is based on the idea that the groups of
electrons (often called electron domains) around
the central atom will repel one another to get as
far away from each other as possible.
• Each non-bonding pair, single bond or multiple
bond produces an electron domain around the
central atom.
• There are five possibilities for the arrangement
of groups of electrons around the central atom.
– 2, 3, 4, 5, and 6 groups of electrons
Electron Group Geometry
• These geometries are called electron group
geometries (EGGs) and these are the only
possibilities for this.
Electron Pairs Around
Central Atom
2
3
4
5
6
Electron Geometry
Linear
Trigonal planar
Tetrahedral
Trigonal bipyramidal
Octahedral
Basic Shapes
Molecular Geometries
• Molecular geometries are the shapes of the
molecules when we look at the bonding groups
of electrons.
• The non-bonding groups are the lone pairs and
do affect the geometry slightly.
• The electron domains for non-bonding electron
pairs and multiple bonds exert greater repulsive
forces on adjacent electron domains and therefore
tend to compress bond angles.
• If there are no lone pairs on the central atom, the
molecular and electron group geometries are the
same.
Bond Angles……
• Look back at pictures and models you built
and discuss with table.
Hybrid Orbitals
• Hybrid orbitals are different for each electron
geometry.
Electron Pairs
Electron
Hybrid Orbitals
Around Central
Geometry
Atom
2
Linear
sp
3
Trigonal planar
sp2
4
Tetrahedral
sp3
5
Trigonal
bipyramidal
Octahedral
sp3d
6
sp3d2