Question

Question 3.31 The first (ΔiH1) and the second (ΔiH) ionization enthalpies (in kJ mol–1) and the (ΔegH) 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)?

Class XI Classification of Elements and Periodicity in Properties Page 94

Answer 1

concept :- metal has positive electron gain enthalpy. and low ionisation energy .
but non - metal has negative electron gain enthalpy and high ionisation enthalpy.


(a) the least reactive element is element ( V ) because it has highest first ionisation enthalpy and electron gain enthalpy ( positive) is positive.

(b) The most reactive metal is element ( II ) because it has least first ionisation enthalpy and also electron gain enthalpy is negative .

(c) The most reactive non - metal is element ( III ) because it has high ionisation energy and least electron gain enthalpy .

(d) The least reactive non - metal is element ( IV ) because it has no so high ionisation enthalpy and but it has high negative electron gain enthalpy.

(e) The metal which can form a stable binary halide of the formula MX2 is element ( VI). element ( VI ) is alkaline earth metal because it has low first ionisation enthalpy but higher than that of alkali metals. Moreover the difference between first and 2nd ionisation enthalpy is very less .

(f) element I has low first ionisation enthalpy but very high 2nd ionisation enthalpy. it has less negative electron gain enthalpy so, it is alkali metal. also the difference between 1st and 2nd ionisation enthalpy is very high.

Answer 2

Explanation:

(a) The element V is the least reactive element as it has highest value of first ionization energy and positive electron gain enthalpy.

(b) The metal II is the most reactive metal. It has very low value of first ionization energy.

(c) The element III is the most reactive non metal. Its electron gain enthalpy is most negative.

(d) The element IV is the least reactive non metal as it has least negative electron gain enthalpy among the non metals.

(e) The metal VI can form a stable binary halide of the formula MX

2

as it has lowest value of second ionization enthalpy.

(f) The metal I can form a stable MX halide