Question

Discuss the factors affecting electron gain enthalpy and the trend in its variation in the periodic table.

Accepted Answer

Factors Affecting Electron Gain Enthalpy:

(i) Nuclear charge: The electron gain enthalpy becomes more negative as the nuclear charge increases. This is due to the greater attraction for the incoming electron if the nuclear charge is high.
(ii) Size of the atom: With the increase in the size of the atom, results in lesser attraction. Consequently, the electron gain enthalpy becomes less negative with the increase in the size of the atom of the element.
(iii) Electronic configuration: The elements having stable electronic configurations of half-filled and completely filled valence subshells show the very small tendency to accept additional electron and thus electron gain enthalpies are less negative.

Variation of electron gain enthalpies in the periodic table:
(a) Variation down a group: On moving down a group, the size and nuclear charge increases. But the effect of an increase in atomic size is much more pronounced than that of nuclear charge and thus the additional electron feels less attraction by the large atom. Consequently, electron gain enthalpy becomes less negative.
(b) Variation along a period: On moving across a period, the size of the atom decreases and nuclear charge increases. Both these factors result in greater attraction for the incoming electron, therefore, electron gain enthalpy, in general, becomes more negative in a period from left to right.

However, certain irregularities are observed in the general trend. These are mainly due to the stable electronic configurations of certain atoms.
There are some important features of electron gain enthalpies of elements. These are:
(i) Halogens have the highest negative electron gain enthalpies.
(ii) Electron gain enthalpy values of noble gases are positive while those of $Be, Mg, N$ and $P$ are almost zero.
(iii) Electron gain enthalpy of fluorine is unexpectedly less negative than that of chlorine.

NCERT Solutions for Chapter: Classification of Elements and Periodicity in Properties, Exercise 1: Long Answer Type

NCERT Chemistry Solutions for Exercise - NCERT Solutions for Chapter: Classification of Elements and Periodicity in Properties, Exercise 1: Long Answer Type

Questions from NCERT Solutions for Chapter: Classification of Elements and Periodicity in Properties, Exercise 1: Long Answer Type with Hints & Solutions

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