ChemWhiz ReferenceCompounds & Naming
Common Ions and Their Charges
Reference table of common monatomic and polyatomic ions with their charges and formulas. Essential for writing chemical formulas and naming compounds.
01Use this when
Writing formulas and naming ionic compounds by balancing total positive and negative charge to zero.
02Conditions
Charges shown are the common, most-stable ion for each species.
03Watch out
Many transition metals form more than one charge; name them with a Roman numeral, e.g. iron(II) vs iron(III).
Common Monatomic and Polyatomic Ions
Names, formulas, and charges for writing and naming ionic compounds.
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| Sodium | Na+ | +1 | Monatomic cation |
| Potassium | K+ | +1 | Monatomic cation |
| Lithium | Li+ | +1 | Monatomic cation |
| Silver | Ag+ | +1 | Monatomic cation |
| Ammonium | NH4+ | +1 | Polyatomic cation |
| Magnesium | Mg2+ | +2 | Monatomic cation |
| Calcium | Ca2+ | +2 | Monatomic cation |
| Barium | Ba2+ | +2 | Monatomic cation |
| Strontium | Sr2+ | +2 | Monatomic cation |
| Zinc | Zn2+ | +2 | Monatomic cation |
| Iron(II) | Fe2+ | +2 | Monatomic cation |
| Iron(III) | Fe3+ | +3 | Monatomic cation |
| Copper(I) | Cu+ | +1 | Monatomic cation |
| Copper(II) | Cu2+ | +2 | Monatomic cation |
| Aluminum | Al3+ | +3 | Monatomic cation |
| Lead(II) | Pb2+ | +2 | Monatomic cation |
| Mercury(I) | Hg22+ | +2 (pair) | Polyatomic cation |
| Mercury(II) | Hg2+ | +2 | Monatomic cation |
| Fluoride | F- | -1 | Monatomic anion |
| Chloride | Cl- | -1 | Monatomic anion |
| Bromide | Br- | -1 | Monatomic anion |
| Iodide | I- | -1 | Monatomic anion |
| Oxide | O2- | -2 | Monatomic anion |
| Sulfide | S2- | -2 | Monatomic anion |
| Nitride | N3- | -3 | Monatomic anion |
| Hydroxide | OH- | -1 | Polyatomic anion |
| Nitrate | NO3- | -1 | Polyatomic anion |
| Nitrite | NO2- | -1 | Polyatomic anion |
| Sulfate | SO42- | -2 | Polyatomic anion |
| Sulfite | SO32- | -2 | Polyatomic anion |
| Hydrogen sulfate | HSO4- | -1 | Polyatomic anion |
| Thiosulfate | S2O32- | -2 | Polyatomic anion |
| Carbonate | CO32- | -2 | Polyatomic anion |
| Hydrogen carbonate (bicarbonate) | HCO3- | -1 | Polyatomic anion |
| Phosphate | PO43- | -3 | Polyatomic anion |
| Hydrogen phosphate | HPO42- | -2 | Polyatomic anion |
| Dihydrogen phosphate | H2PO4- | -1 | Polyatomic anion |
| Acetate | CH3COO- | -1 | Polyatomic anion |
| Permanganate | MnO4- | -1 | Polyatomic anion |
| Chromate | CrO42- | -2 | Polyatomic anion |
| Dichromate | Cr2O72- | -2 | Polyatomic anion |
| Perchlorate | ClO4- | -1 | Polyatomic anion |
| Chlorate | ClO3- | -1 | Polyatomic anion |
| Chlorite | ClO2- | -1 | Polyatomic anion |
| Hypochlorite | ClO- | -1 | Polyatomic anion |
| Cyanide | CN- | -1 | Polyatomic anion |
| Oxalate | C2O42- | -2 | Polyatomic anion |
| Thiocyanate | SCN- | -1 | Polyatomic anion |
Important Notes
- Group 1 metals (Li, Na, K, Rb, Cs) always form +1 ions.
- Group 2 metals (Be, Mg, Ca, Sr, Ba) always form +2 ions.
- Transition metals often form multiple ion charges (e.g., Fe2+ and Fe3+). Use Roman numerals in names.
- The -ate suffix generally indicates more oxygen atoms; -ite indicates fewer (e.g., sulfate SO42- vs sulfite SO32-).
- The per- prefix means one more oxygen than -ate; hypo- prefix means one fewer than -ite.
- Mercury(I) is unusual: it exists as a diatomic ion Hg22+, not as a simple Hg+.
Verification references: OpenStax Chemistry 2e, Section 2.6 (Table 2.5 for the polyatomic ions; monatomic-ion names and charges from the same section's monatomic-ion and Stock-name discussion).