Question

Which of the given pairs of elements would have a more negative electron gain enthalpy? F or Cl?

Answer 1

cl has more electron gain enthalpy because even though fluorine is highly electronegative it has very small valence shell.when another electron is added it tries to repel whereas in cl valence shell is comparatively larger.

Answer 2

The Fluorine (F) and (Cl) belong to the same 17th group of the periodic table and they are p block elements with fluorine belonging to 2nd period and chlorine to 3rd group of periodic table.

The electron gain enthalpy usually becomes less -ve on moving down a group.

Here, the value of the electron gain enthalpy of Cl is more -ve than that of F because of very small size of F atom.

So there are strong interelectronic repulsions in the relatively small 2p subshell of F & thus the incoming electron does not feel much attraction.

Therefore its electron affinity is small.