The electron affinities of the elements from aluminum to chlorine are - 44, - 120, - 74, - 200.4, and - 384.7 kJ/mol, respectively. Rationalize the trend in these values.

Electron affinity increases when moving left to right of the period.

Explanation:

Electron affinity is the amount of energy released when an isolated gaseous atom accepts electron to form the corresponding anion.

Trend of electron affinity across the period:-

Across the period, the electron affinity increases as there is an increase in effective nuclear charge. Due to this, there is more force of attraction between the nucleus and the valence electrons when moving left to right in a period. Thus, more amount of energy is released when an electron is being gained in the neutral atom to form anion. Thus, electron affinity increases when moving left to right of the period.

Thus,

Al : - 44 kJ/mol

Si : - 120 kJ/mol

P : - 74 kJ/mol

S : - 200.4 kJ/mol

Cl : - 384.7 kJ/mol

Al, Si, P, S, Cl are the members of third period and thus, left to right, the electron affinities of the elements increases as can be seen from the literature values.