Question

what do you mean by co-ordination number of an ionic crystal?

Answer 1

coordination number in ionic crystals mean oppositely charged ions surrounding the particular cation or anion. For eg. Na+ ion in NaCl crystal is surrounded by 6 Cl- ion and Cl- is surrounded by 6 Na+ ion. Therefore Coordination number is 6 :6. In CaF2 Ca2+ ion is surrounded by 8 F- ions and each F- ion by 4 Ca 2+ ion. Therefore C.N is 8:4.