The attraction between two neutral atoms is the result of their polarizations aligning. You can visualize it something like this.
The negative electron cloud surrounding a positive nucleus oscillates back and forth due to quantum effects. When two atoms are put very close to each other, these oscillations start to align. This means that the positive nucleus of one atom can pull on the negative electron cloud of the other, and vice-versa. As a result, the atoms pull each other together.
This is the origin of the attractive Van der Waals force that, among other things, allows geckos to climb on walls.
For a more complete description, see: [ Ссылка ]
