A nonpolar molecule is made of two or more atoms where the electronegativity difference between the atoms is less than 0.5. Therefore, the electron density in the bond is equally distributed, and there is no concentration of electrons on one atom to create a charge separation rendering the molecule essentially without poles or nonpolar. Such nonpolar molecules like H2, CH4, He, etc., will interact using the London dispersion forces without forming any positive or negative pole.
The electrons in nonpolar molecules are not stationary but are continuously moving. The electrons' positions undergo random fluctuations, resulting in an occasion where the concentration of electrons is more towards one part of the molecule than the other. This forms an electron-rich and an electron-deficient end creating a temporary dipole. The molecules near these temporary dipoles also undergo distortions in their electron cloud, creating induced dipoles. Consequently, all the temporary induced dipoles align according to their charges, so that opposite charges attract, and the molecules closely interact. This force of attraction holding the nonpolar molecules close is the London Dispersion force.
This is additional content for the chapter Intermolecular Forces in CurlyArrows' Introduction to Organic Chemistry Course. Preview the Book.
Related Reading:
Introduction to the Vander Waal Forces