To find the formulae, you must add as many of the ions together to get a neutral charge. For example, one Li^+ ion and one NO2^- ion give LiNO2, which is lithium nitrite, but since CO3^2- has a charge of -2, it needs 2 Li^+ ions to make the neutral compound Li2CO3, lithium carbonate. Similarly, Cu^2+ needs 2 NO2^- ions to make the neutral compound Cu(NO2)2, copper(II) nitrite. To name these, simply add together the names of the ions used. Li^+ is lithium, Cu^2+ is copper(II), and Ba^2+ is barium. The negatively charged ions are named as nitrite for NO2^-, carbonate for CO3^2-, bisulfate for HSO4^- and phosphate for PO4^3-.
