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

Question

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

Luna Chen · Accepted Answer

A molecule of an element contains only the one type of atom........

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, #"compounded together"#: viz. #HX#, #H_2O#, #CH_4#, #NH_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?

Noah Aldrich · Answer

undefined Non-molecular species include elements that exist as individual atoms (e.g., noble gases) or ionic compounds where ions are arranged in a lattice structure instead of discrete molecules. A molecular element is made up of atoms of the same element bonded together, whereas a molecular compound is made up of atoms of different elements bonded together.