In which of the following liquids are the Van der Waals forces of attraction between the molecules weakest?

A. Xe
B. Kr
C. Ar
D. Ne
E. He


Dear Student

Vanderwaal forces are caused due to instantaneous polarisibility introduced in a molecule.

For example: Like noble gases due to random motion acquires partially negative charge and partially positive charge for an instant (due to free electron cloud motion due to randomness). This very short time span Charge separation causes vanderwaal interaction.

Now, larger the size, more is the surface area and bigger is the electron cloud. This will lead to more separation of charge and stronger vanderwaal interaction among the molecules of the specie.

As we go down the group, size increases, electron cloud increases and as a result vanderwaal interaction or forces become stronger.

So, we can conclude that vanderwaal forces are directly proportional to the size of the molecule or element.

From the above options, He is the smallest and thus have the weakest vanderwaal interaction among it's molecules. 


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