Question

Which statement is correct about antifluorite structure of Na${}_2$O ?

• A. $O^{2-}$ ions have CCP arrangement.
• B. $N{a}^{+}$ ions occupy all the tetrahedral sites.
• C. It has $4:8$ coordination.
• D. All the above.

Answer 1

The correct option is D All the above.

Each $C{a}^{2+}$ ion is surrounded by $8F^{-}$ ions i.e. it has a co-ordination number of $8$ whereas each $F^{-}$ ion is surrounded by $4C{a}^{2+}$ ions i.e. has a co-ordination number of $4$. Thus, this structure has $8:4$ co-ordination.

In $N{a}_{2}O$, each oxide ion is co-ordinated to $8N{a}^{+}$ ions and each $N{a}^{+}$ ions and each $N{a}^{+}$ ion to $4$ oxide ions. Hence, it has $4:8$ co-ordination. This is called anti-fluorite structure. Other examples being $C{l}_{2}O,K_{2}O,L{i}_{2}O,K_{2}S,N{a}_{2}S$ etc.