Question

Which of the following element has the highest electron-gain enthalpy?

• A. oxygen
• B. neon
• C. chlorine
• D. fluorine

Answer 1

The correct option is C

chlorine

The explanation of the correct option:

C) Chlorine

• Electron gain enthalpy is defined as the energy released when an electron is added to an isolated atom.
• It can be exothermic or endothermic according to the nature of that atom.
• Halogens have the highest electron gain enthalpy in the periodic table and noble gases have the least electron gain enthalpy.
• out of all the halogens, Chlorine has the highest electron gain enthalpy followed by Fluorine, bromine, and then iodine.
• The reason for this is that the Chlorine atom has a small size and needs only one electron to complete its octet which results in a release of a huge amount of energy.

Explanation of incorrect options:

A) Oxygen

• Oxygen needs two electrons to complete its octet and because it just needs two electrons, the electron gain enthalpy of oxygen is high as well.
• After the halogens group, chalcogens (group 16) have the second-highest electron gain enthalpy.
• But, it has a larger size than the Chlorine atom and requires two electrons, it releases lesser enthalpy than that of a chlorine atom.

B) Neon

• Neon belongs to group 18 which are known as noble gases.
• Noble gases have the least electron gain enthalpy as their octet is already completed and generally it is hard for an electron to enter into a new shell since they are very stable atoms.

D) Fluorine

• Fluorine has the second-highest electron gain enthalpy in the entire periodic table after Chlorine.
• The reason is that compared to chlorine, fluorine has a smaller size which creates interelectronic repulsions within the 2p orbital.
• Due to this, it is hard for an electron to enter the atom easily.

Hence, option C) Chlorine is correct.