What is the co-ordination number of sodium in `Na_(2)O` ?

Options

A. 6
B. 4
C. 8
D. 2

Answer

B

Explanation

The compound `Na_(2)O` has anti–fluorite structure. The `O^(2-)` ions are arranged in ccp arrangement. The `Na^(+)` ions occupy all the tetrahedral holes. Since there are two tetrahedral holes for each `O^(2-)` ion, there will be two `Na^(+)` ions for each `O^(2-)` ion, thus the stoichiometry of the compound is 2 : 1 .
Each `O^(2-)` ion is surrounded by `8Na^(+)` ions and each `Na^(+)` ion is surrounded by `4O^(2-)` ions. Thus the C.N . Of `O^(2-)` ion is 8 and that of `Na^(+)` ion is 4.