Question

The energy released when an electron is added to a neutral gaseous isolated atom to form a negatively charged ion is called as:

Answer 1

Hint:The energy release in the process of adding an electron to a neutral gaseous isolated atom and forming a negatively charged ion is called electron affinity. It is known to be a potential energy change of an atom. We must know that the more negative the electron affinity the more favorable the process of electron addition is.

Complete step-by-step answer:We must know that not all elements form stable negative ions in which case the electron affinity is zero or even positive. When we look at the periodic trends, the electron affinities are not easy to measure.
As we move from left to right across a period, the electron affinity increases. This is known to occur due to an increase in nuclear attraction.
As we go down the group, we can see that the electron affinity decreases. This occurs as the electron is being added further away from the nucleus more and more causing the bond to weaken and thus losing an electron is easier.
Atomic size decreases as we move from left to right across a period due to the increase in nuclear forces and thus we know that the electron gain enthalpy increases. Whereas while moving down a group we can see that the atomic size constantly increases thereby causing a decrease in the value of electron gain enthalpy.
Factors which affect electron affinity are –
1.Atomic size
2.Effective nuclear charge
3.Screening effect

Note: It is important to note that first electron affinity is always exothermic. This means that negative the second electron affinity of the same element will be positive or endothermic. This is so because the second electron has to be forced to enter the mono negative ion. The electron affinity cannot be determined directly but is obtained indirectly from the Born-Haber cycle.