What is the major difference between a nonmolecular and molecular substance?
When multiple atoms covalently bond to form a new species, each particle of this species is called a molecule, and the molecules are collectively called a molecular compound. For example, when hydrogen and oxygen atoms bond, they form water molecules, and thus, water is a molecular compound. Note that, when two or more atoms of the same species from covalent bonds together, this is still a molecular substance. For example, particles of diatomic gases like H2, O2, and N2 are called molecules, and these species are molecular compounds. If a substance is not molecular, it might be atomic (like a metal, for example) or it might be ionic (like salt, i.e. sodium chloride). Although multiple atoms are bonded to one another in these substances, the bonding is not covalent, and therefore the substances are not molecular.
