The first (ΔiH1) and the second (ΔiH2) ionization enthalpies (in kJ mol⁻¹) and the (ΔegH) electron gain enthalpy (in kJ mol⁻¹) of a few elements are given below: Elements ΔH1 ΔH2 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) and (f) the metal which can form a predominantly stable covalent halide of the formula MX (X=halogen)?

The first (ΔiH1) and the second (ΔiH2) ionization enthalpies (in kJ mol⁻¹) and the (ΔegH) electron gain enthalpy (in kJ mol⁻¹) of a few elements are given below:
Elements ΔH1 ΔH2 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) and
(f) the metal which can form a predominantly stable covalent halide of the formula MX (X=halogen)?

Solution:

(a) The element V is the least reactive element as it has the highest value of first ionization energy and positive electron gain enthalpy.
(b) The metal II is the most reactive metal. It has a very low value of first ionization energy.
(c) The element III is the most reactive non-metal. Its electron gain enthalpy is the most negative.
(d) The element IV is the least reactive non-metal as it has the least negative electron gain enthalpy among the non-metals.
(e) The metal VI can form a stable binary halide of the formula MX2 as it has the lowest value of second ionization enthalpy.
(f) The metal I can form a stable MX halide.

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