Chem172- Chapter 11

VSEPR theory

A model that allows us to account for molecular shape, it is based on the idea that electron groups repel one another through coulombic forces

Lone pairs

a pair of valence electrons that does not participate in a covalent bond and belongs to a single atom

Electron groups

Lone pairs, single bonds, double bonds, triple bonds

Electron groups around a central or interior atom will be …. when they are…

most stable; as far apart as possible

2 electron groups:…

Linear

3 electron groups:…

Trigonal planar

linear angle

180

Trigonal planar bond angles

120

4 electron groups:…

tetrahedral

tetrahedral bond angles

109.5

5 electron groups:…

trigonal bipyramidal

The angles in the trigonal bipyramidal structure are ….

not all the same. Angles between equatorial positions is 120, bonds between axial and equatorial is 90

6 electron groups:…

octahedral

octahedral bond angles

90

Lone pairs typically…than bonding electrons, affecting…

exert slightly greater repulsion than bonding electrons, affecting bond angles

Why is a lone electron pair more spread out in space than a bonding electron pair

A lone pair is attracted to only one nucleus while a bonding pair is attracted to 2 nuclei

Are lone pairs localized?

can be either

Delocalization

When multiple structures are possible, the molecule actually exists as an average of all its resonance structures. Electrons become delocalized, so that they are spread out throughout the molecule.