The trends that we have seen in chemical properties of the second-row elements and their oxides can be extended to the heavier elements as well. Atoms with few outer electrons are metals, and their oxides are basic.

In solution the metal ions surround themselves with a hydration shell of water molecules, attracted to the ions only by electrostatic forces. Somewhat more electronegative atoms are at the borderline between metals and nonmetals. Their oxides are both acidic and basic, and are termed amphoteric.

Even more electronegative atoms are clearly nonmetals, and complete their outer electron shell by either sharing electrons, or becoming ions by picking up the missing electrons if only one or two are needed. Their oxides are acidic. In solution, the attraction for oxygen is so strong that each central atom is surrounded by a shell of covalently bonded O atoms. The result is an oxyanion such as carbonate, , and nitrate, . The acidity of such compounds is increased by stabilization of the ions via delocalized electrons.

Finally, if the electronegativity of the atom is greater than that of oxygen (true only for F), then the electrons are not shared between the central atom and O in covalent bonds, but are pulled away from the O atoms entirely. The result is not an oxyion, but a simple ion. This behavior will not be seen again in heavier elements, because none of them are more electronegative than oxygen.