Question

The element with highest electron affinity will belong to:
A. Period 2, group 17
B. Period 3, group 17
C. Period 2, group 18
D. Period 2, group 1

Answer 1

Hint: To solve this question we should know that the elements which will tend to release the highest amount of energy on adding an electron in the outermost orbital of the isolated gaseous atom will have the highest electron affinity in the periodic table. Electron affinity increases as we move across the period and decreases down the group.

Complete Solution :
- Electron affinity is defined as the amount of energy released when an electron is added in the outermost shell of an isolated gaseous atom to form the negative ion. The other name of electron affinity is electron gain enthalpy.
- As we know that for an element the electron affinity depends on the following factors, like number of protons and the size of the atom. The trend of the electron affinity in the periodic table is given as:
- As we move from left to right in the periodic table electron affinity increases because the size decreases whereas on moving down the group electron affinity will decrease.
- When we will see the periodic table we can say that the electron affinity of the halogens which belong to group 17 of the periodic table have the highest electron affinity as compared to others. This happens due to the high effective nuclear charge present on the nucleus and due to the small size of all the halogens.
- So, we can say that the electron affinity of the fluorine atom which belongs to halogen may have the highest electron affinity but this is not the case because chlorine have the highest electron affinity because the size of the fluorine is very small and if we will add the electrons in the valence shell then it will face the repulsion from the other electrons that are present in the 2p orbital of fluorine.
- Therefore we can conclude that the chlorine will have the highest electron affinity and it belongs to period 3, group 17 of the periodic table.
So, the correct answer is “Option B”.

Note: Fluorine is the most electronegative among the halogen group but its electron affinity is less than chlorine due to interelectronic repulsion. The decreasing order of the electron affinity seen in the halogen group is Chlorine > Fluorine > Bromine > Iodine and it should be remembered.