Question

Which of the following pairs is not the correct order of lattice energy?

• A. $KCl>MgO$
• B. $AlN>MgO$
• C. $CaO>BaO$
• D. $MgC{O}_3>CaC{O}_3$

Answer 1

The correct option is A $KCl>MgO$

As the charge on the ions (cations and anions) increase, the lattice energy increases, and it decreases when the size of the ions (cations and anions) increases.

a) Size: $K^{+}>M{g}^{2+}$
Charge: $+1<+2$
Size: $C{l}^{-}>O^{2-}$
Charge: $-1<2-$
Thus, the lattice energy of $MgO$ is greater than $KCl$.

b) Size: $A{l}^{3+}<M{g}^{2+}$
Charge: $+3>+2$
Size: $N^{3-}>O^{2-}$
Charge: $-3>-2$
Here, the charge factor dominates and hence the lattice energy of $AlN$ is greater than $MgO$.

c) Size: $C{a}^{2+}<B{a}^{2+}$
Charge: $+2=+2$
Size: $O^{2-}=O^{2-}$
Charge: $-2=-2$
The lattice energy of $CaO$ is greater than $BaO$.

d) Size: $M{g}^{2+}<C{a}^{2+}$
Charge: $+2=+2$
Size: $C{O}_3^{2-}=C{O}_3^{2-}$
Charge: $-2=-2$
The lattice energy of $MgC{O}_3$ is greater than the $CaC{O}_3$.