But before we start naming them, there’s one more secret that the periodic table holds. Did you notice the numbers surrounding the table’s rows and columns? The numbers before its rows are called its period numbers, whereas the numbers above the columns of the table are called its group numbers. You also might have noticed that the group numbers come in both Arabic numerals and Roman numerals. In modern times, the IUPAC numbers columns from 1 to 18, however, classically, they used Roman numerals. The system of Roman numerals in the table above, however, is a bit different than the classic IUPAC version. This one, created by the Chemical Abstract Service (CAS), an American organization, separates main elements with the letter “A” and transition metals with “B”.

Whichever you use, the group helps you locate an element based on coordinates. However, they can be helpful in characterizing behavior, as we’ll see when we name molecular ions in a moment.

Overall, when naming molecular ions with oxyanions, there are two prefixes and two suffixes, organized in four different ways. The two prefixes are “hypo-” and “per-”, while the two suffixes are “-ite” and “-ate”.

Usually, if the core atom in the ion is from Groups 7A/B or 8 and it’s bonded to one oxyanion, the name will have a “hypo-” prefix and an “-ite” suffix if it. If it’s bonded to two ions, the name only contains an “-ite” suffix. For three, the name contains an “-ate” suffix. Lastly, four ions adds the prefix “-per” on top of the “-ate” suffix.