Question

The element with highest electron affinity in the periodic table is?

A. Iodine

B. Chlorine

C. Fluorine

D. Oxygen

Answer 1

Hint: We should remember that the element which will release the most amount of energy on adding an electron in its isolated gaseous atom will posse’s highest electron affinity in the periodic table.

Complete Step by Step Solution:

Electron affinity is defined as, “The amount of energy released when an electron is added to the outermost shell of a neutral atom or molecule in the isolated gaseous state to form a negative ion.

Electron affinity is also referred to as “Electron gain enthalpy”.

We should know that, for any element, electron affinity depends on factors like the number of protons present and the size of the atom.

On moving from left to right along a period in the periodic table, we will notice that electron affinity increases while on moving down the group, electron affinity tends to decrease.

Out of all the groups present in the periodic table, halogens have high electron affinity compared to others. This is due to the small size of all halogen atoms and high effective nuclear charge present on the nucleus.

So, on the above ground’s fluorine should have the highest electron affinity but that is not the case.

It has been seen that chlorine is the highest. This happens due to small size of fluorine atom due to which if any electron is added in its valence shell, it faces repulsion from the other electrons present in  $ 2p $  orbital but that is not the case with chlorine atom in which the electron to be added goes in  $ 3p $  orbital which has larger size as compared to  $ 2p $  orbital of fluorine atom .

Therefore, it has been concluded that among all the options present above option B is the correct answer.

Note: The energy released on adding an electron in the fluorine atom is used up in countering the interelectronic repulsion.

The decreasing order of electron affinity among halogen is- chlorine>fluorine>bromine>iodine should be remembered.