Question

Which of the following elements has highest electron gain enthalpy ?
a.) Oxygen
b.) Fluorine
c.) Chlorine
d.) Neon

Answer 1

The electron gain enthalpy may be defined as the energy released when a neutral atom accepts an electron. Higher the energy released, greater is the value of electron gain enthalpy. In simple terms, the atom that can most easily hold the electron, meaning the atom that has a high nucleus charge will have the highest electron gain enthalpy. The small size atoms can not hold extra electrons easily.

Complete step by step answer:
The electron gain enthalpy is the amount of energy released when an electron is added to an isolated neutral gaseous atom. It can be defined as the strength of the nucleus by which it binds the extra electron.
On moving left to right, the nucleus charge increases and the size of the atom decreases. As a result, the pulling power of the nucleus increases. So, the electron gain enthalpy also increases.
The noble gases are most stable and do not require any electron. So, they have very low electron gain enthalpy. Thus, the neon can-not be the answer.
On the other hand, the halogen belonging to the 17th group has the highest electron gain enthalpy.
Further, on moving down the group, the electron affinity decreases. So, the fluorine should be the answer. But the Fluorine atom due to its very small size feels electron-electron repulsions and thus, can-not hold extra electrons.
Thus, the correct answer is Chlorine.
So, the correct answer is “Option C”.

Note: It must be noted that the halogens require only one electron to achieve noble gas configuration. So, the halogens will easily acquire one electron and thus, have the highest electron gain enthalpy. Further, on moving left to right, with increase in nuclear charge, the pull of nucleus towards valence electrons also increases. So, it makes halogen the highest energy donors.