Lecture 4

Overview Details

This lecture is best summarized by Pauling's Rules, as listed below

Pauling's Rules:

1. The Coordination (radius ratio) Principle – a coordination polyhedron of anions surrounds each cation. The cation-anion distance is determined by the sum of the cation and anion radii and the number of anions coordinating with the cation is determined by the relative size of the cation and anion.

2. Electrostatic Valency Principle – in a stable ionic structure, the total strength of the valency bonds that reach an anion from all neighboring cations is equal to the charge of the anion.

3. Sharing of Polyhedral Elements I – the existence of edges (and particularly faces) common to coordination polyhedra decreases the stability of ionic structures

4. Sharing of Polyhedral Elements II – in a crystal containing different cations, those with large valence and small coordination number tend not to share polyhedral elements with each other.

5. Principle of Parsimony – the number of essentially different kinds of constituents in a crystal tends to be small.