Explanation:
When an electron is added to a neutral atom to convert it into a negative ion then the amount of change taking place in its energy is known as electron affinity.
Smaller is the size of an atom more readily an electron will be gained by it because of strong force of attraction exerted by its nucleus towards the electron.
So, on moving down a group there will occur a decrease in electron affinity of the atoms. Also, size of atoms decreases from left to right in a periodic table. Therefore, electron affinity will also increase on moving from left to right.
As elements of group 15 are half filled so, they are more stable in nature and have slightly less electron affinity as compared to group 14 elements.
Thus, we can conclude that the trends and exceptions to the trends in electron affinity are as follows.
Trends in electron affinity is that it decreases down a group and exception are the electron affinities of the elements in Group 17 are larger (more negative) than the elements in Group 1 and Elements in Group 14 have larger (more negative) electron affinities than elements in Group 15.
Electron affinity is the power of the addition of any upcoming electron to the neutral atom for the formation of a new anion, and in this process we always get a negative value of electron affinity as in this process energy is released.
Electron affinity is inversely proportional to the atomic size of given atom.
Group 17 is the group of noble gases which are most stable configuration, that's why they have highest electron affinity. And the outermost shell of group 15 elements are half filled, so they will show very less interest in the addition of electron and bearing a very less electron affinity as compare to group 14 elements.
Hence, electron affinity increases down a group, group 17 has highest electron affinity and electron affinity of group 14 is larger than group 15.
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