Question

Increasing order of electron gain enthalpy of group 16 is:

Answer 1

Although there is a slight difference between the two, electron gain enthalpy is frequently referred to as electron affinity. The amount of energy released when an electron is added to an isolated gaseous atom is known as electron gain enthalpy. Energy can be released or absorbed with the addition of an electron.

Complete answer:
When an electron is delivered to an atom to produce a negative ion, the change in energy (in kJ / mol) of a neutral atom is called electron affinity (in the gaseous phase). In other words, the chance of an electron being acquired by a neutral atom. It's also known as the amount of energy released when an electron is attached to a neutral atom or molecule in a gaseous state and forms a negative ion.
In general, electron affinity may be defined as the acceptance of an incoming electron by the atom of that element.
The electron affinity of elements is determined by a number of parameters, including the size of the atom, its electron gain enthalpy, and its position in the periodic table.
The elements oxygen, sulphur, and selenium are all found in the same group in the periodic table, in the order oxygen, sulphur, selenium. The size of the elements grows larger as we progress along the group, but the electron gain enthalpy decreases.
According to electron gain enthalpy, the order of electron affinity must be highest in oxygen and lowest in selenium.
However, due to the oxygen atoms' lowest size within the group, there is a large repulsion to the incoming electron due to their tiny size. As a result, selenium's electron affinity must be the highest in terms of size. Sulphur and selenium, on the other hand, are not that dissimilar in size.
When the effects of size and electron gain enthalpy are combined, sulphur's electron affinity is slightly greater than selenium's, while oxygen's is the lowest in the group.
As a result, the proper electron affinity order is
$O(-141.4kJ\text{ }mo{{l}^{-1}}) < Po(-174kJ\text{ }mo{{l}^{-1}}) < Te(-190.0kJ\text{ }mo{{l}^{-1}}) < Se(-195.5kJ/mol) < S(-208.8kJ\text{ }mo{{l}^{-1}})$

Note:
As we progress through the group, the electron gain enthalpy gets less negative. In addition, when we travel from left to right in a periodic table, the electron gain enthalpy gets increasingly negative. This is due to the fact that the effective nuclear charge varies.