Question

In the case of hydrogen and helium, the Van der Waal's forces are
(A) Very strong
(B) Strong
(C) Weak
(D) None of the above

Answer 1

Hint: Van der Waals’s force of attraction is the intermolecular forces that exist between the molecules. The molecules develop the charges through the induced dipole moment. The charge that is developed can be permanent or temporary.

Complete step by step answer:
Van der Waals forces are intermolecular forces that are weak and it depends on the distance between atoms or molecules. Interactions between uncharged atoms or molecules lead to these forces.
Van der Waal's forces are weak interactions that are attractive between atoms and molecules that are much weaker than ordinary chemical bonds.
Hydrogen bonds involve interactions between permanent dipoles, they can be considered as a type of Van der Waals force ( Keesom interactions). However, hydrogen bonds are stronger than another type of Van der Waals forces (Such as Debye forces and London dispersion forces)
In (He) helium is a gas at temperatures above 4 K. In this condition two hydrogen approach one another they form a much more stable interaction, about 1000 times stronger than the He – He London dispersion forces.
Van der Waal forces between helium atoms are so weak.
The attractive interactions of dipoles with each other, combined with weaker dipole/induced-dipole and dispersion forces, accounts for the ability of most substances to condense into liquids and solids.
The force between hydrogen and helium are weak because of London-London dispersion forces.

So, the correct answer is Option C.

Note: Any dipole- dipole interactions in atoms or molecules can be described by ‘Van der Waals force’. Van der Waals forces are distance-dependent forces. The interaction is maximum when the distance between the molecule is less.