Question

Question #16078

Answer 1

`"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.


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.