Common Anions and Their Formulas (Page 1)

Common Ions: Names and Formulas

Cation

• ammonium: $\mathrm{NH_4^+}$

Anions

• nitrite: $\mathrm{NO_2^-}$

• nitrate: $\mathrm{NO_3^-}$

• sulfite: $\mathrm{SO_3^{2-}}$

• sulfate: $\mathrm{SO_4^{2-}}$

• hydrogen sulfate (bisulfate): $\mathrm{HSO_4^-}$

• thiosulfate: $\mathrm{S<em>2O</em>3^{2-}}$

• oxalate: $\mathrm{C<em>2O</em>4^{2-}}$

• hydroxide: $\mathrm{OH^-}$

• phosphite: $\mathrm{PO_3^{3-}}$

• phosphate: $\mathrm{PO_4^{3-}}$

• hydrogen phosphate: $\mathrm{HPO_4^{2-}}$

• dihydrogen phosphate: $\mathrm{H<em>2PO</em>4^-}$

• perchlorate: $\mathrm{ClO_4^-}$

• chlorate: $\mathrm{ClO_3^-}$

• chlorite: $\mathrm{ClO_2^-}$

• hypochlorite: $\mathrm{ClO^-}$

• bromate: $\mathrm{BrO_3^-}$

• acetate: $\mathrm{CH<em>3COO^-}$\ (also written as $\mathrm{C</em>2H<em>3O</em>2^-}$)

• carbonate: $\mathrm{CO_3^{2-}}$

• hydrogen carbonate (bicarbonate): $\mathrm{HCO_3^-}$

• chromate: $\mathrm{CrO_4^{2-}}$

• dichromate: $\mathrm{Cr<em>2O</em>7^{2-}}$

• permanganate: $\mathrm{MnO_4^-}$

• peroxide: $\mathrm{O_2^{2-}}$

• cyanide: $\mathrm{CN^-}$

• cyanate: $\mathrm{OCN^-}$

• thiocyanate: $\mathrm{SCN^-}$

Notes on patterns and common usage

• -ate vs -ite suffixes indicate more oxygen typically in the ion; e.g., chlorate (ClO3^-) vs chlorite (ClO2^-), chromate (CrO4^{2-}) vs dichromate (Cr2O_7^{2-}).
• Hydrogens in anion names indicate acidic forms or protonated forms (e.g., bicarbonate HCO3^-, dihydrogen phosphate H2PO4^-, hydrogen sulfate HSO4^-).
• Acetate has two common formulæ: $\mathrm{CH<em>3COO^-}$ and $\mathrm{C</em>2H<em>3O</em>2^-}$ (same ion).
• Common salts arise by pairing these anions with cations (e.g., ammonium nitrate $\mathrm{NH<em>4NO</em>3}$, sodium sulfate $\mathrm{Na<em>2SO</em>4}$).
• Charge balance is essential in naming and formula writing: typical charges are as shown, and many ions occur with 1-, 2-, or 3- charges depending on oxidation state and composition.
• Some ions have alternative conventional names (e.g., bicarbonate vs hydrogen carbonate; bisulfate for HSO_4^-).

Quick reference: how to read the formulas

• A superscript indicates charge: e.g., $\mathrm{NO_3^-}$ has -1 charge.
• A subscript indicates the number of atoms: e.g., $\mathrm{C<em>2O</em>4^{2-}}$ has two carbons and four oxygens with a -2 charge.
• When multiple oxygens are present with a single charge, the charge is placed after the formula: e.g., $\mathrm{SO_4^{2-}}$.