Question

Rand the comounds from highest to lowest magnitude of their lattice energy

LiCl Na2S MgO BeO Na2O

Answer 1

We have to decide the magnitude of lattice energies of given compounds based on the sizes of the ions and distance between the ions of the compounds. Observe the relation between the lattice energy and the ionic sizes and charges present on the ions with the help of given equation below---

U  ? Q₁ Q₂ / R    (Q1 AND Q2 ARE CHARGES ON THE IONS AND R IS THE DISTANCE BETWEEN THEM IN A COMPOUND ,   U IS THE LATTICE ENERGY)

LiCl will have the lowest magnitude of LE( lattice energy), because the product of charge of its ions is 1*1 =1.

between Na₂S and Na₂O sodium ion is common so the compare the size of the ions between O and S. we have S is bigger size (down the group six) so Na₂S is lower magnitude than Na₂O.

between MgO and BeO Mg and Be having same charge of +2 , and Be is the smaller ion compared to Mg . O is the common in both of the compounds. so Mg is the compound having lower LE.

bwtween Mg O and Na₂O Mg is +2 and Na is +1 so the magnitude of LE is lower for Na₂S than MgO

So based on the argument as above we can arrange the compounds in the order of HIGHEST TO LOWEST order of their LE as follows.

BeO > MgO >   Na ₂O > Na₂S > LiCl