Van Der Waals Forces: Overview, Questions, Preparation

In this topic, we are going to learn about Van Der Waals Forces, intermolecular forces. Van Der Waals Forces can be defined as the pull of attraction caused by bonding in molecules or atoms. These interactions are intended towards molecules lying without charge because the electrostatic forces within the range start acting up. These are also termed as the weakest molecular range consisting of the dipole to dipole dispersion. The main cause for these forces to occur resides behind the fluctuation that takes place in the polarization of at least two particles located at a very near distance.

These Van Der Waals Forces are considered the weakest chemical forces because as soon the distance between two particles starts increasing at a molecular interaction level, the intermolecular forces quickly vanish. It should be noted that these electrostatic forces attract uncharged molecules towards each other but in all states or forms – solids, liquids, and gas.   

In the below-mentioned equation, one can observe the main two kinds of properties present – the first being the volume of both the elements and the second being the attractive forces in-between. The equation is as follows:

1. Van Der Waals Forces are significantly weaker as they are electrostatic, but covalent and ionic bonds are much stronger than Van Der Waals Forces.
2. Saturation of Van Der Waals Forces isn’t possible.
3. Van Der Waals Forces doesn’t have any attributed sense of direction.
4. These forces do not depend upon temperature.

Keesom Interactions

These interactions are electrostatic and occur because of the charges present in the ionic molecules. This type is named after a Ditch physicist Willem Hendrick Keesom. These are temporary interactions and only take place between two permanently existing dipoles.

Debye Forces

These are the causes of induced dipoles, which take place between permanent dipoles and some of the other atoms. Unlike Keesom, this takes place between permanent and no temporary dipoles.

London Dispersion Forces

These interactions are caused because the main reason behind these is the instantaneous dipole attraction towards another molecule. These are the weakest type of Van Der Waals Forces.

As per the latest published CBSE syntax for marks and its breakdown, this chapter of States of Matter holds a weightage of 5 marks in total. It contains 1 very short question of 2 marks each and one short question for 3 marks each. This brings the overall weightage of this chapter to 5 marks in total.

1. Provide an example of London Dispersion forces.

Answer:

2. Provide an example of VDW between an induced dipole and a permanent dipole.

Answer:

3. What is the range of VDW forces?

Answer: The range of VDW forces is between 0.4 kJ.mol-1 to 4 kJ.mol-1.

[Image courtesy: NCERT]

Q: Name one factor which affects the strength of Van Der Waals Forces.

Q: Explain saturation in Van Der Waals Forces.

Q: Does Van Der Waals Forces depend upon temperature?

Q: Which is the weakest type of Van Der Waals Forces.

Q: Name one type of Van Der Waals Forces.