Question

Which of the following will have the most negative electron gain enthalpy and which the least negative? $P,S,Cl,F.$ Explain your answer.

Answer 1

Electron gain enthalpy is defined as the amount of energy released when an electron is added to an isolated gaseous atom. During the addition of an electron, energy can either be released or absorbed.

Electron gain enthalpy generally becomes more negative across a period as we move from left to right. Within a group, electron gain enthalpy becomes less negative down a group.

Halogens have highest negative value of electron gain enthalpy due to small size and high $Z_{effect}.$
Here $Cl$ and $F$ both are halogen but electron gain enthalpy of $Cl$ is more negative than $F$ because of adding an electron to the $2p-orbital$ leads to greater repulsion than adding an electron to the larger $3p-orbital$ (small size of $F$ which causes interelectronic repulsion among its electrons).

So, $Cl$ has the most negative electron gain enthalpy .

$P$ has the least negative electron gain enthalpy because of its more stable half-filled electronic configuration.

Overall order of electron gain enthalpy for halogen family follows as$:Cl>F>Br>I$

Final answer: $Cl$ has the most negative electron gain enthalpy and $P$ has the least negative electron gain enthalpy.