Question #16078

1 Answer
Ernest Z. · Stefan V. · Michael
Jan 28, 2015

#"Cl"# has a higher electron affinity than #"F"# because electronic repulsions are greater in the smaller #"F"# atom.

Explanation:

Electron affinity is the enthalpy change when 1 mol of gaseous atoms each gain an electron to form 1 mol of gaseous ions.

It is the enthalpy change for:

#X_((g)) + e^(-) rarr X_((g))^-#

For fluorine the electron affinity = #"-328 kJ·mol"^"-1"#

For chlorine the electron affinity= #"-349 kJ.mol"^"-1"#

So, we can see that the value for chlorine is larger and negative compared with fluorine.

Both #"Cl"# and #"F"# are quite happy to accept an electron to complete their octet and get to a lower energy level.

But #"F"# is a smaller atom, so the electrons are crowded together more closely.

The electron repulsions are greater in the #"F"# atom, so there is not as much energy available to be released when the electron is added.

https://www.xtremepapers.com/revision/a-level/chemistry/inorganic/group7/properties.php

Fluorine, since it's such a small atom, has a very high electron density, which means that the repulsion the incoming electron feels will diminish the attraction coming from the nucleus and thus reduce its electron affinity.

Related questions
See all questions in Periodic Trends in Electron Affinity
Impact of this question
8990 views around the world
You can reuse this answer
Creative Commons License