whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers hydroxide The two common polyatomic ions whose names end in -ide are cyanide and _ oxygen In a polyatomic ion, the -ite ending indicates one fewer __atom that the -ate ending. polyatomic anion An -ite or -ate ending on the name of a compound indicates that the compound Roman numeral following the name When naming an ion of a transition metal that has more than one common ionic charge, the numerical value of the charge is indicated by a: