Question

Select correct statement(s) about radius of an atom:
A. Values of Van der waals’ radii are larger than those of covalent radii because the van der waals’ forces are much weaker than the forces operating between atoms in a covalently bonded molecule.
B. The metallic radii are smaller than the van der waals’ radii, since the bonding forces in the metallic crystal lattice are much stronger than the Van der Waals forces.
C. Both (A) and (B) are correct.
D. None of the above is correct.

Answer 1

The distance covering the path in between the nuclei of the two bonded atoms is known as the internuclear distance. Half of this internuclear distance is the radius of an atom. The radius of the atom in which van der waal forces are present is called the van der waal radii.

Complete step-by-step answer: When atoms of two gases come close together, then weak force between them comes into action through the electron clouds of both the gases. This force is known as Van der Waal forces. Another instance of these forces is seen in the molecules of gases, when they are liquefied and converted into solids. The van der waal force arises due to the formation of a temporary dipole between the atoms.
Van der waals’ forces are weaker and observed in neutral molecules. These weak forces tend to increase the size of the compounds with them. So, the radius in those molecules is known as van der waals’ radii.
When compared to covalent and metallic radii, van der waal radii are larger. This is because, in metallic compounds the atoms are closely packed together and metallic forces exist that are very strongly bonded, which results in the smaller size of metallic radii. While in covalent radii, the atoms are bonded together through covalent forces, these forces are formed by sharing of electrons and results in a strongly packed structure that decreases the covalent radii. So the order of radii is,
Van der waal radii > metallic radii > covalent radii

Hence, option C is correct as the statements (a) and (b) both are right, which suggests the same mentioned reason for the large size of van der waal radii.

Note: Van der waal forces are of 2 types, London forces or dispersion forces, and dipole-dipole forces. Both of these forces are considered as weak forces. These forces are present in all organic liquids as well as solids.