Question

Which of the following trends in lattice energy is due to differences in ionic radii?

Which of the following trends in lattice energy is due to differences in ionic radii?

MgO> NaCl

CaO> CaBr2

NaCl> RbBr> CsBr

All of the above

Answer 1

Correct answer is c) NaCl> RbBr> CsBr

Lattice energy of a crystal is dependent on two factors, charge on its ions and ionic radii.

If charge is more, the lattice energy will be high and hence, crystal will be difficult to collapse.

If ionic radii is more, then charge separation will be more and hence, lattice energy will be less.

a) MgO has higher lattice energy than NaCl because in MgO charges are +2 and -2 which are more in magnitude than +1 and -1 in NaCl.

b) CaO has higher lattice energy than CaBr₂ both due to charge difference as well as ionic radii of O^2- being smaller than Br^-.

c) All the salts, NaCl, RbBr and CsBr are having same charges i.e. +1 and -1. So, the difference is due to ionic radii only.

NaCl has smallest cation and anion and so, it has maximum lattice energy. Cs has larger cationic radii than Rb, so CsBr has lowest lattice energy of the three salts.