text: An ionic compound is named by its cation followed by its anion. See polyatomic ion for a list of possible ions.
  For cations that take on multiple charges, the charge is written using Roman numerals in parentheses immediately following the element name. For example, Cu(NO) is copper(II) nitrate, because the charge of two nitrate ions () is 2 × −1 = −2, and since the net charge of the ionic compound must be zero, the Cu ion has a 2+ charge. This compound is therefore copper(II) nitrate. In the case of cations with a +4 oxidation state, the only acceptable format for the Roman numeral 4 is IV and not IIII.
  The Roman numerals in fact show the oxidation number, but in simple ionic compounds (i.e., not metal complexes) this will always equal the ionic charge on the metal. For a simple overview see [http://www.cofc.edu/~deavorj/101/nomenclature.html] , for more details see [http://www2.potsdam.edu/walkerma/inorg_naming.pdf selected pages from IUPAC rules for naming inorganic compounds] .