# How do we differentiate between a "molecular element", and a "molecular compound"? And how are these differentiated from "non-molecular" species?

The distinction between a molecular and non-molecular structure is one of the most important criteria with which to assess bonding. But here, if we have an elemental molecule, we have (to a first approx.) only the one type of atom in the molecule: viz. ${H}_{2}$, ${N}_{2}$, ${O}_{2}$ etc........
A molecular compound contains AT LEAST two elements, $\text{compounded together}$: viz. $H X$, ${H}_{2} O$, $C {H}_{4}$, $N {H}_{3}$, but the material is composed of discrete molecules of formula units. The force of attraction BETWEEN molecules determines the physical properties of the bulk substance, for instance melting and boiling points. How do you think the intermolecular force varies between the given compounds..........and what bulk property could we use to measure the magnitude?