The coordination number of an ion in a crystal lattice is
- A. the number of oppositely charged ions immediately surrounding it
- B. the charge on the ion
- C. the number of unit cells it belongs to
- D. the number of electrons it has lost or gained
Explanation
Coordination number counts the nearest neighbours of opposite charge, so it is six in sodium chloride and eight in caesium chloride, the difference arising from the relative sizes of the ions. A larger cation can accommodate more anions around it before they begin to touch each other. The number of electrons transferred determines the charge, which is a separate quantity.