In a hexagonal-close-pack (hcp) unit cell, the ratio of lattice points to octahedral holes to tetrahedral holes is 1: 1: 2.

what is the general formula for a compound if anions occupy the hcp lattice points and cations occupy all the octahedral holes? what is the general formula for a compound if anions occupy the hcp lattice points and cations occupy all the octahedral and tetrahedral holes?

Explanation:

In a hexagonal-close-pack (HCP) unit cell, the ratio of lattice points to octahedral holes to tetrahedral holes =  1 : 1 : 2

let the :

Number of lattice point = 1x.

Number of octahedral points = 1x

Number of tetrahedral  points = 2x

If anions occupy the HCP lattice points and cations occupy half of the octahedral holes.

Number of anions occupying the HCP lattice points, A= 1x

Number of cations occupying the octahedral points, B =  1x

The formula of the compound will be =

If anions occupy the HCP lattice points and cations occupy all of  the octahedral and the tetrahedral holes.

Number of anions occupying the HCP lattice points, A= 1x

Number of cations occupying the octahedral points, B =  x

Number of cations occupying the tetrahedral points, B =  2x

total number of cations = x + 2x = 3x

The formula of the compound will be =