What is the origin of electromagnetic interaction between molecules? Anyway, it should have some relation with atoms. Also, These electromagnetic interactions are playing a major role in different properties of matter including the transition between solid-liquid-gas. Hence, what would be the **source** of these interactions..?

If these interactions originate from atoms, then some other questions come into **focus**:

* Are they related to the transition of electrons between various energy levels and emission of photons from an atom..?
* Are they related to [cohesive](http://en.wikipedia.org/wiki/Cohesion_%28chemistry%29) forces between molecules in solids & liquids?