Question

1.(a) MgO has the rock-salt structure. The MgO crystal has a value of 0.514 for the radius ratio. The length of a side of the unit cell for MgO is 4.24 Å.

(i) Draw the structure of this molecule.

(ii) Determine the radii of Mg ²⁺and O^2-, assuming that the O ^2-ions are in contact with one another.

(b) Define what is meant by the “coordination number” of a crystal structure.

(c) Determine the coordination number for each of the following crystal structures:

(i) Face-centred cubic (NaCl)

(ii) Body-centred cubic (CsCl)

(iii) Zinc blende (ZnS)

Answer 1