Question

depending on temperature, RbCl can exist in either the rock-salt or cesium-chloride structure. what is the coordination number of the cation and the anion in each of these structures? *** please explain everything you do ***

Answer 1

The rock salt structure is Closest-packed. The cations occupy the octahedral holes, so have 6 nearest neighbour aniona a coordination number of 6. Rb in RbCl has 5 of the 6 nearest neighbours. The anions also have 6 nearest neighbours that are cations, so also have a coordination number of 6. The atom labeled Cl has 4 of the 6 nearest neighbours.

The Cesium Chloride structure is not closest packed. The cation at the centre of the unit cell has 8 nearest neighbours, so the coordination number is 8. The chloride also have 8 nearest neighbours, the cations in the center of all the surrounding unit cells.