33. 4 Some Rules Governing the Ionic Compounds Pauling's three rules governing the structure of ionic compounds 1. Anion Coordination polyhedron rule Each cation is surrounded by an anion polyhedron, the distance between anion and cation is r=rt tr, while the CN depends on rt
§3.4 Some Rules Governing the Ionic Compounds Pauling’s three rules governing the structure of ionic compounds. 1. Anion Coordination polyhedron rule Each cation is surrounded by an anion polyhedron, the distance between anion and cation is ro ＝r +＋r - , while the CN depends on r +/r-
unstable r>+r r++ stable ionic compound stable there is some covalent bounding
ro＞r +＋r－ ro ＝r +＋r－ stable ionic compound ro＜r +＋r－ there is some covalent bounding stable unstable
Coordination Cation-Anion Coordination Aumber Radins Ratio Geometry 55 3 0.1550.225 0.225-0.414 0.4140.732
anion CN+ polyhedron hexahedron 0.732 octahedron 0.414 tetrahedron 8—6-4—3 0.225 trigonal 0.155
anion polyhedron CN＋ ( )min hexahedron 8 0.732 octahedron 6 0.414 tetrahedron 4 0.225 trigonal 3 0.155 − + r r
2 Valence rule There is a definite relation between valence and CN Let s be the strength of electrostatic bonding between a pair of anion and cation
2. Valence rule There is a definite relation between valence and CN. Let S be the strength of electrostatic bonding between a pair of anion and cation