Chemistry - PERIODIC TABLE Question with Solution | TestHub

Positive ions having 4 or more than 4 positive charges have more polarizing power converting into covalent compounds. Isoelectronic ionic compounds need not have same lattice energy as the charges on the ions may be different $(exKF,CaO\&ScN)$. The strong electrostatic attraction between the ${\mathrm{Ca}}^{2+}$ and ${\mathrm{O}}^{2-}$ ion causes more liberation of lattice energy, that compensate the energy required in the formation of ${\mathrm{Ca}}^{2+}$ and ${\mathrm{O}}^{2-}$ ions. Lattice energy is proportional to $\frac{Q_1+Q_2}{r_c+r_a}\cdot Q_1\&Q_2$ are same for $KBr$ and CsCl. From $K^{+}$to ${\mathrm{Cs}}^{+}$size increases but from ${\mathrm{Br}}^{-}$to CI size decreases. So the value in denominator also become nearly equal causing nearly same LE.