Van der Waals interactions:

Van der Waals interactions are the most weak of the intermolecular bonding forces and include the transient presence of partial charges in a molecule. Electrons are repeatedly moving in an unpredictable way around any molecule. At any minute of time, there is in one part of the molecule a slight excess of electrons and a slight de?cit in other part. Even though the charges are extremely weak and vary around the molecule, they are adequately strong to permit a weak interaction among the molecules in which regions of opposite charge in dissimilar molecules attract each other.

Alkane molecules can be interacting in this manner and the strength of the interaction rises with the size of the alkane molecule. Van der Waals interactions are as well significant for alkenes, alkynes and aromatic rings. The kinds of molecules included in this type of intermolecular bonding are 'fatty' molecules that do not dissolve easily in water and such type of molecules are known as hydrophobic (water- hating). Hydrophobic molecules may be dissolves in nonpolar, hydrophobic solvents because of van der Waals interactions and thus this form of intermolecular bonding is occasionally considered to as a hydrophobic interaction.