Question

Which of the following atoms has a minimum covalent radius
A. B
B. C
C. N
D. Si

Answer 1

Hint: When a covalent bond exists between two atoms, the covalent radius comes into the picture.
If two atoms of the same element have a covalent bond, the radius of every atom involved will be one-half of the length between the two nuclei as both atoms equally draw electrons towards themselves.

Complete step by step solution:As we move across or down the periodic table, covalent radii change.
The effective nuclear charge of an atom is the total positive charge experienced by the valence electron.
It greatly influences the atomic size of an atom.
Some positive charge is shielded or screened by the inner orbital electrons so the total positive charge is not experienced by the valence electron.
If effective nuclear charge reduces, the radius will expand.
It is because there will be an additional screening of the electrons belonging to the nucleus, reducing the attraction between the nucleus and the electron.
Since effective nuclear charge reduces going down a group, size increases.
If we move from the right-hand side to the left-hand side across the periodic table, the radius decreases.
As we move right to left in a periodic table we get B, C, and N.
So, N has the smallest covalent radius as the radius decreases along a period.
If we move down the group from C to Si, the radius increases. So, the radius of Si is more than C.
So, N has the smallest covalent radius.

So, option C is correct.

Note: Electrons are negatively charged and are drawn rather near each other for their appeal to the positive charge of a nucleus.
The nucleus draws the electrons towards itself but the electrons repel each other. The balance between attractive and repulsive forces gives rise to shielding.
The inner orbital electrons sense a more powerful pull toward the nucleus than any other electron within the system.
The valence electrons are distant from the nucleus, so they feel less force of attraction.
Shielding is the repulsion of the inner orbital electrons and the outer orbitals.