Question

Question #9ce3c

Answer 1

Definition: Electron gain is the amount of energy released when one mole of electron is added to a gaseous atom.

Explanation:

Both F and Cl are found in the same Group VII, so they have the same number of 7 valence electrons. As Cl is below F in the Group, Cl has one more electron shell than F, hence Cl has a larger atomic nucleus, so the distance between the nucleus and valence shell (where the gained electron will be at) is smaller in F as compared to that in Cl. This suggests that in Chlorine, the forces of attraction from the nucleus to the gained electron is lower, and as bond forming is exothermic, less energy is given out in the forming of bonds between the nucleus and the electron.

Therefore, electron gain enthalpy in Cl is lower than that in F.

Answer 2

The reason is that `"F"` has a greater charge density.

Explanation:

Electron gain enthalpy (`Δ_text(eg)H`) is the change in enthalpy when an electron in added to an atom in the gaseous state.

`color(blue)("X(g) + e"^"-" → "X"^"-""(g)")`

`Δ_text(eg)H` depends on two factors:

• the electronegativity of `"X"`, i.e., its attraction for incoming electrons
• the environment into which the electron enters.

`"F"` is more electronegative than `"Cl"`, so we would expect it to have a more negative value of `Δ_text(eg)H`.

However, `"F"` is a smaller atom than `"Cl"`. It has about one-fifth the volume of a `"Cl"` atom.

It has a higher electron density, so there will be a greater repulsion of the incoming electron.

In a `"Cl"` atom, the electron is entering a `"3p"` orbital rather than a `"2p"` orbital, so the electron repulsions are much smaller.

The result is that `Δ_text(eg)H` is more negative for `"Cl"` than for `"F"`.

(Adapted from chemistry Assignment)

We see the same effect with `"O"` and "`S"`.