positive ions.

• aluminum Al³⁺
• barium Ba²⁺
• bismuth Bi³⁺
• cadmium Cd²⁺
• calcium Ca²⁺
• cesium Cs⁺
• chromium (III) Cr³⁺
• cobalt Co²⁺
• copper (I) Cu⁺
• copper (II) Cu²⁺
• hydrogen H⁺
• iron (II) Fe²⁺
• iron (III) Fe³⁺
• lead (II) Pb²⁺
• lithium Li⁺
• magnesium Mg²⁺
• mercury (I) Hg₂²⁺
• nickel Ni²⁺
• potassium K⁺
• rubidium Rb⁺
• silver Ag⁺
• sodium Na⁺
• strontium Sr²⁺
• tin (II) Sn²⁺
• zinc Zn²⁺

Examples of Negative Ions

Just as atoms can lose electrons to become cations, some can gain electrons and become negatively charged anions. Again, you may be familiar with some of these ions. Fluoride is sometimes added to community water supplies. Your dentist may also give you a fluoride treatment.

The negative charge (fewer protons than electrons) for an anion is shown by a number and minus sign after the formula. If there’s just a minus sign, it means the charge is minus 1. Review several examples of anions.

• bromide Br^–
• chloride Cl^–
• fluoride F^–
• iodide I^–
• nitride N^3-
• oxide O^2-
• sulfide S^2-

Polyatomic Cations and Anions

If an ion consists of two or more atoms, it is called a polyatomic ion. Just like their single-atom counterparts, they too can gain and lose electrons.

Polyatomic Cations

Ions with multiple atoms that lose electrons, and are thus positively charged, are called polyatomic cations.

• Ammonium NH₄⁺
• Hydronium H₃O⁺

Polyatomic Anions

Ions with multiple atoms that gain electrons, and are thus negatively charged, are called polyatomic anions. Per standard notation, the charge is written as superscript text.

• acetate CH₃COO^– or C₂H₃O^2-
• arsenate AsO₄^3-
• bicarbonate or hydrogen carbonate HCO₃^–
• borate BO₃^3-
• carbonate CO₃^2-
• chlorate ClO₃^–
• chlorite ClO₂^–
• chromate CrO₄^2-
• cyanide CN^–
• dichromate Cr₂O₇^2-
• dihydrogen phosphate H₂PO₄– or H₂O₄P^–
• formate CHO₂^– or HCOO^– or CHOO^–
• hydrogen sulfate or bisulfate HSO₄^–
• hydrogen sulfite or bisulfite HSO₃^–
• hydrogen phosphate HPO₄^2-
• hydroxide OH^–
• hypochlorite ClO^–
• nitrate NO₃^–
• nitrite NO₂^–
• oxalate C₂O₄^2-
• perchlorate ClO₄^–
• permanganate MnO₄^–
• peroxide O₂^2-
• phosphate PO₄^3-
• phosphite PO₃^3-
• silicate SiO₃^2-
• sulfate SO₄^2-
• sulfite SO₃^2-
• thiocyanate SCN^–
• thiosulfate S₂O₃^2–