11.2 VSEPR Theory: The Five Basic Shapes

What does VSEPR stand for?

Valence Shell Electron Pair Repulsion

What are electron groups

as lone pairs, single bonds, multiple bonds, and even single electrons

What is VSEPR theory based on?

the simple idea that electron groups repel one another through coulombic forces. The electron groups are also attracted to the nucleus (otherwise the molecule would fall apart), but VSEPR theory focuses on the repulsions.

What determines the geometry of a molecule?

the repulsions between electron groups on interior

atoms of a molecule determine the geometry of the molecule

The preferred geometry of a molecule is the one in which the electron groups have maximum separation (and therefore minimum repulsion energy).

For molecules having just one interior atom (the central atom), molecular geometry depends on what two factors?

-the number of electron groups around the central atom;

-how many of those electron groups are bonding groups and how many are lone pairs.

What are the five electron geometries?

linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral

Linear Geometry

Two electron groups around the central atom; Bond angle of 180 degrees

Trigonal Planar Geometry

three electron groups can maximize their separation by assuming 120 degree bond angles in a plane

Tetrahedral Geometry

4 e- pairs, sp3 hybridization

angles 109.5

0 lone pairs: tetrahedral (four bonds) [CH4, NH4+, ClO4-, SO4 2-, PO4 3-]

1 lone pair: trigonal pyramidal (3 bonds) [NH3, PCl3, SO3 2-]

2 lone pairs: bent (2 bonds) [H2O, OF2, NH2-]

Trigonal Bypyramidal Geometry

5 bonding, 0 lone pair; 120 degrees (equatorial), 90 degrees (axial)

Octahedral Geometry

6 e- pairs, sp5 hybridization

0 lone pairs: octahedral (6 bonds) [SF6]

1 lone pair: square pyramidal (5 bonds) [BrF5, IF5]

2 lone pairs: square planar (4 bonds) [XeF4]