The Shapes of Molecules and Ions from the VSEPR Theory

The VSEPR Theory: it is the arrangement of atoms in molecules and ions

This theory is applied in the following way:

Consider molecules (or ions) in which the central atom is covalently bonded to two or more atoms or groups

Consider all the valence electron pairs of the central atom-both those that are shared in covalent bonds, called bonding pairs, and those that are unshared, called non-bonding pairs or unshared pairs.

Because electron pairs repel each other, the electron pair of the valence shell tend to stay far apart as possible. The repulsion between non-bonding pairs is generally greater than that between bonding pairs.

The geometry of the molecule is arrived at by considering all of the electron pairs, bonding and non-bonding, but the shape of the molecule or ion is described by referring to the positions of the nuclei (or atoms) and not by the position of the electron pairs.

Problems:

Use the VSEPR theory to predict the geometry of each of the following molecules and ions:

a)BH4- b)BeF2 c) NH+ 4 d) H2S e)BH3 f) CF4