Question

The correct order of atomic radius of Li, Be and B is:
A. B> Li > Be
B. Li > B > Be
C. Li > Be > B
D. B> Be > Li

Answer 1

Hint: >The periodic table is designed in such a way that elements are put in increasing order of their atomic masses and surprisingly, their physical and chemical properties are the same within a group or block. Hence, the atomic radius decreases moving from left to right in a period.

Complete Solution :
- Atomic Radius is the distance from the atom’s nucleus to the outermost shell of the atom. When you are moving from left to right in a period then, effective nuclear charge ( the net positive charge, the electrons can feel as the core electrons will cloud the valence electrons to feel the attraction from) increases. This higher effective nuclear charge pulls the electrons towards itself, which causes the decrease in the radius and hence the lesser atomic radius.
- The elements Lithium belongs to the first group and Be belongs to the second group but Boron belongs to the 13th group and since they lie in the same 1st period therefore, moving from left to right the atomic radius will decrease. Hence, the correct order would be Li > Be > B.
So, the correct answer is “Option C”.

Note: If we look at the atomic radius trend in a group then it increases when moving from top to down as there is addition of shells in the atom when you move down the group.