Chemical Nomenclature: Formulas, Oxidation States & Naming

Posted on Mar 27, 2025 in Chemistry

Chemical Nomenclature Fundamentals

Oxidation States and Acid Naming Conventions

The name of an oxyacid depends on the oxidation state of the central non-metal atom (X). Prefixes (hypo-, per-) and suffixes (-ous, -ic) are used as follows:

Note: The exact formula (number of H atoms) depends on the group the central element belongs to.

Common Element Valences (Oxidation States)

• Hydrogen (H): 1
• Lithium (Li): 1
• Sodium (Na): 1
• Potassium (K): 1
• Silver (Ag): 1
• Fluorine (F): -1 (typically)
• Beryllium (Be): 2
• Magnesium (Mg): 2
• Calcium (Ca): 2
• Barium (Ba): 2
• Zinc (Zn): 2
• Oxygen (O): -2 (except peroxides -1, superoxides -1/2)
• Boron (B): 3
• Aluminum (Al): 3
• Silicon (Si): 4
• Copper (Cu): 1, 2
• Mercury (Hg): 1, 2
• Gold (Au): 1, 3
• Chlorine (Cl): -1, 1, 3, 5, 7
• Bromine (Br): -1, 1, 3, 5, 7
• Iodine (I): -1, 1, 3, 5, 7
• Iron (Fe): 2, 3
• Nitrogen (N): -3, 1, 2, 3, 4, 5
• Phosphorus (P): -3, 3, 5
• Antimony (Sb): -3, 3, 5
• Lead (Pb): 2, 4
• Carbon (C): -4, 2, 4
• Tin (Sn): 2, 4
• Sulfur (S): -2, 2, 4, 6
• Chromium (Cr): 2, 3, 6
• Manganese (Mn): 2, 3, 4, 6, 7

Exceptions and Special Cases in Acid Naming

Manganese Acids

• Manganous acid: H₂MnO₃ (Mn oxidation state +4)
• Manganic acid: H₂MnO₄ (Mn oxidation state +6)
• Permanganic acid: HMnO₄ (Mn oxidation state +7)

Chromium Acids

• Chromic acid: H₂CrO₄ (Cr oxidation state +6)
• Dichromic acid: H₂Cr₂O₇ (Cr oxidation state +6)

Phosphorus, Antimony, Arsenic, Boron Acids

These elements can form acids with different numbers of hydrogen atoms, often indicated by prefixes like meta-, pyro-, and ortho-, depending on the degree of hydration.

Compound Naming Rules and Examples

Oxides

Formed with oxygen (O^2-). Simplify formulas if possible.

• Na₂O: Sodium oxide / Disodium monoxide
• Cl₂O₇: Chlorine(VII) oxide / Dichlorine heptoxide
• CO: Carbon(II) oxide / Carbon monoxide

Peroxides

Contain the peroxide ion (O₂^2-). Formulas are generally not simplified.

• For metals with valence +1: Cu₂O₂ – Copper(I) peroxide / Dicopper dioxide
• For metals with valence +2: MgO₂ – Magnesium peroxide / Magnesium dioxide

Metallic Hydrides

Formed between metals and hydrogen (H^–).

• LiH: Lithium hydride / Lithium monohydride
• CrH₆: Chromium(VI) hydride / Chromium hexahydride

Non-Metallic Hydrides

Formed between non-metals and hydrogen. Some have common names.

• BH₃: Boron trihydride / Borane
• NH₃: Nitrogen trihydride / Ammonia
• PH₃: Phosphorus trihydride / Phosphine
• AsH₃: Arsenic trihydride / Arsine
• SbH₃: Antimony trihydride / Stibine
• CH₄: Carbon tetrahydride / Methane
• SiH₄: Silicon tetrahydride / Silane
• HF: Hydrogen fluoride (gas) / Hydrofluoric acid (aqueous solution)
• H₂Te: Hydrogen telluride

Binary Salts

Typically formed from a metal cation and a non-metal anion.

• NaCl: Sodium chloride
• FeBr₃: Iron(III) bromide / Iron tribromide
• CrS₃: Chromium(VI) sulfide / Chromium trisulfide
• PCl₃: Phosphorus(III) chloride / Phosphorus trichloride
• NH₄Cl: Ammonium chloride (contains polyatomic cation)

Oxoacids (Oxyacids)

Acids containing hydrogen, oxygen, and another element (non-metal).

• HClO: Hypochlorous acid / Monoxochlorate(I) of hydrogen
• HClO₄: Perchloric acid / Tetraoxochlorate(VII) of hydrogen
• H₂SO₄: Sulfuric acid / Tetraoxosulfate(VI) of hydrogen
• H₂CO₃: Carbonic acid / Trioxocarbonate(IV) of hydrogen

Oxoacid Salts

Formed when the hydrogen ions of an oxoacid are replaced by metal ions or ammonium ions. Suffixes change as follows:

• Acid suffix hypo-…-ous becomes Salt suffix hypo-…-ite
• Acid suffix -ous becomes Salt suffix -ite
• Acid suffix -ic becomes Salt suffix -ate
• Acid suffix per-…-ic becomes Salt suffix per-…-ate

Examples:

• NaClO: Sodium hypochlorite / Sodium monoxochlorate(I)
• Cu(ClO₄)₂: Copper(II) perchlorate / Copper(II) tetraoxochlorate(VII)
• Al₂(CO₃)₃: Aluminum carbonate / Aluminum trioxocarbonate(IV)
• NH₄NO₃: Ammonium nitrate / Ammonium trioxonitrate(V)

Hydroxides

Contain metal cations (or ammonium) and hydroxide ions (OH^–). The metal’s oxidation state indicates the number of OH^– groups.

• Cr(OH)₃: Chromium(III) hydroxide / Chromium trihydroxide
• NaOH: Sodium hydroxide
• NH₄OH: Ammonium hydroxide

Acid Salts

Salts formed from polyprotic acids where not all acidic hydrogens have been replaced. They contain hydrogen ions that can potentially be donated.

• NaHS: Sodium hydrogen sulfide / Sodium bisulfide
• Ca(HS)₂: Calcium hydrogen sulfide / Calcium bisulfide
• NaH₂PO₄: Sodium dihydrogen phosphate / Sodium dihydrogen tetraoxophosphate(V)
• NaHCO₃: Sodium bicarbonate / Sodium hydrogen carbonate / Sodium hydrogen trioxocarbonate(IV)