Helium and hydrogen molecules. Computer artwork of molecules of helium and hydrogen,the two lightest and most abundant elements in the universe. Helium (He) is a monatomic chemical element,meaning every molecule of the gas comprises only one atom. Each atom consists of a nucleus (orange),surrounded by an electron cloud (pink),which contains two electrons orbiting in a single energy level. Hydrogen (H2),however,is a diatomic molecule. Each atom has a nucleus (dark green) surrounded by an electron cloud (light green),containing only one electron. Therefore in a gaseous state (as is seen here),two atoms will combine to form a covalently bonded molecule,which has two electrons orbiting the nucleus,increasing its stability |