Question

The first (Δ_iH1) and the second (Δ_iH) ionization enthalpies (in kJ mol^–1) and the (Δ_egH) electron gain enthalpy (in kJ mol^–1) of a few elements are given below:

Elements	ΔiH	ΔiH	ΔegH
I	520	7300	–60
II	419	3051	–48
III	1681	3374	–328
IV	1008	1846	–295
V	2372	5251	+48
VI	738	1451	–40

Which of the above elements is likely to be :

(a) the least reactive element.

(b) the most reactive metal.

(c) the most reactive non-metal.

(d) the least reactive non-metal.

(e) the metal which can form a stable binary halide of the formula MX₂, (X=halogen).

(f) the metal which can form a predominantly stable covalent halide of the formula MX (X=halogen)?

Answer 1

(a) Element V is likely to be the least reactive element. This is because it has the highest first ionization enthalpy (Δ_iH₁) and a positive electron gain enthalpy (Δ_egH).

(b) Element II is likely to be the most reactive metal as it has the lowest first ionization enthalpy (Δ_iH₁) and a low negative electron gain enthalpy (Δ_egH).

(c) Element III is likely to be the most reactive non–metal as it has a high first ionization enthalpy (Δ_iH₁) and the highest negative electron gain enthalpy (Δ_egH).

(d) Element V is likely to be the least reactive non–metal since it has a very high first ionization enthalpy (Δ_iH₂) and a positive electron gain enthalpy (Δ_egH).

(e) Element VI has a low negative electron gain enthalpy (Δ_egH). Thus, it is a metal. Further, it has the lowest second ionization enthalpy (Δ_iH₂). Hence, it can form a stable binary halide of the formula MX₂ (X=halogen).

(f) Element I has low first ionization energy and high second ionization energy. Therefore, it can form a predominantly stable covalent halide of the formula MX (X=halogen).