Question

How does chain length affect Van der Waals forces?

Answer 1

Hint:Van der Waals forces are intermolecular forces that are present in all the gases, while in organic solids and liquids. These are weaker electric forces that have the ability to attract the neutral molecules.

Complete step-by-step answer:Van der Waals forces are present in atoms of molecules of most gases and organic compounds (solid and liquid). These forces depend on the position of the electrons in an atom and exert a weak electric force. They are distance dependent forces and their effect is very less on a greater distance.
When a molecule is formed in a chain pattern, Van der Waal forces have an increase in their magnitude. This happens because of the electron density on carbon chains increases that result in more interactions with the atoms and the electrons. So, the Van der Waal forces also get activated and have greater magnitude.
This is also inferred from the fact that, as the chain in any compound increases, the boiling point of that compound increases. This shows that the molecules interact more strongly due to more magnitude of the molecular force, which is Van der Waal force (in organic compounds).
The facts that chain increase the boiling point and hence the Van der Waal force is shown in the boiling points of organic compound, pentane and its isomers as,
n-pentane has boiling point = $36.1{}^\circ C$, isopentane has boiling point = $27.7{}^\circ C$, and neopentane has boiling point = $9.5{}^\circ C$.
This clearly shows that decrease in the chain has weaker Van der Waal forces.
Hence increase in chain length increases the Van der Waal forces.

Note:Van der Waal forces exist in all gases and organic compounds, but except the noble gases interactions. When two noble gases combine, the forces are Dispersion or London forces.