Question

F or Cl which has more negative electron gain enthalpy justify your answer

Answer 1

Oxygen is a p block element present in 16thgroup &2nd period while fluorine is also a p block element present in 17th group & 2nd period. An F atom has one proton and one electron more than O and as an electron is being added to the same shell, the atomic size of F is smaller than that of O. As F contains one proton more than O, its nucleus can attract the incoming electron more strongly in comparison to the nucleus of O atom. Also, F needs only one more electron to attain the stable noble gas configuration. Hence, the electron gain enthalpy of F is more negative than that of O .Fluorine F and Cl belong to the same 17th group of the periodic table & they are p block elements with fluorine belonging to 2nd period & chlorine to 3rd group of periodic table. The electron gain enthalpy usually becomes less negative on moving down a group. However, in this case, the value of the electron gain enthalpy of Cl is more negative than that of F because of very small size of F atom. As a result 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.

Answer 2

cl because the size of the element is bigger than the F