Question

Which of the following has the highest electron affinity?
A. $F$
B. $Cl$
C. $Br$
D. $I$

Answer 1

We know the modern periodic table is based on the properties of an element that are functions of their atomic number. The properties are based on the electronic configuration of the elements. Periodic properties are the trend in properties across a period from left to right to down the group. Some of the important periodic properties are metallic character, non-metallic character, atomic size, electron affinity, ionization potential and electronegativity.

Complete step by step answer:
We can define electron affinity as the energy change of a neutral atom in the vapour phase when an electron is added to the atom to give a negative ion.
Electron affinity of the periodic table decreases down a group because each atom is larger than the above atom. The electron affinity increases across a period as the electrons move closer to the nucleus because of their smaller size and strong force of attraction.
Electron affinity increases from left to right across a period and decreases down the group.
In electron affinity, the atom gains electrons.
Fluorine, chlorine, bromine and iodine belong to the halogen family (group-17).
We know that electron affinity decreases on moving down the group, but chlorine would have more affinity than fluorine because the size of fluorine is smaller than the size of chlorine.
The bigger size of chlorine atom makes it accumulate more electrons and so, its electron affinity is higher.

$\therefore$ Option (B) is correct.

Note:
The trends of electron affinity are,
${\text{Halogens > Oxygen}}\,{\text{family > Carbon}}\,{\text{family > Nitrogen}}\,{\text{family > Metals}}\,{\text{groups}}\,{\text{1}}\,{\text{and}}\,{\text{13 > Metals}}\,{\text{group}}\,{\text{2}}$
From the above trend, we can observe that electron affinities of nonmetals are greater than metals.
The factors that affect electron affinity are atomic size and nuclear charge.
We can define first electron affinity as the energy given out by the first electron when it is added to an atom and it results in the formation of monovalent anion.
Example: The electron affinity of selenium is ${\text{ - 195}}\,{\text{kJ/mol}}$
The electron affinity of germanium is ${\text{ - 119}}\,{\text{kJ/mol}}$
The higher negative electron affinity value, the greater will be the atom’s affinity for electrons. Therefore, selenium has greater electron affinity than germanium.