Rules for Naming Monatomic Ions Positive ions--Cations 2.If a metal can form different cations,the positive charge is indicated by a Roman numeral in parentheses following the name of the metal Common cations of the transition elements: Cr3+:chromium(IID)or chromic Cr2+:chromium(ID)or chromous Hg2+:mecury(II)or mercuric Ag":silver Hg2:mecury(I)or mercurous Zn2+:zinc Co2+:cobalt(II)or cobaltous Cd2+:cadmium Mn2*:manganese(II)or manganous2. If a metal can form dif erent cations, the positive charge is indicated by a Roman numeral in parentheses following the name of the metal Common cations of the transition elements: 3+ 2+ 2+ 2+ 2 2+ 2+ Cr :chromium(III) or chrom Cr :chromium(II) or chrom Hg :mecury(II) or mercur Hg :mecury(I) or mercur Co :cobalt(II) or cobalt Mn :manganese ic ous ic ous ous (II) or manganous + 2+ 2+ Ag :silver Zn :zinc Cd :cadmium