Question

The first $\left(\Delta_i H_1\right)$ and the second $\left(\Delta_i H_2\right)$ ionisation enthalpies $\left({kJ} {mol}^{-1}\right)$ of three elements I, II and III are given below :

	I	II	III
$\Delta_i H_1$	403	549	1142
$\Delta_i H_2$	2640	1060	2080

Identify the element which is likely to be

(i). a non-metal

(ii) an alkali metal

(iii) an alkaline earth metal

Answer 1

(i) Element III is a non-metal. Ionisation enthalpies of non-metals are very high.

(ii) An alkali metal has very low first ionisation enthalpy and much higher second ionisation enthalpy. Therefore, element I is an alkali metal.

(iii) An alkaline earth metal has higher first ionisation enthalpy $\left(\Delta_i H_1\right)$ but lower $\Delta_i H_1+\Delta_1 H_2$ than the alkali metal of the same period. Therefore, element II is an alkaline