Chemical Nomenclature

• Nomenclature is a system of naming things, especially in science
• In chemistry, a consistent nomenclature is essential for clear communication

Common Naming Conventions

• Trivial names are common or historical names that lack a systematic basis
• For example, water (H2O) and ammonia (NH3)
• IUPAC nomenclature is a systematic method of naming chemical compounds recommended by the International Union of Pure and Applied Chemistry

Naming Ionic Compounds

• Ionic compounds are composed of ions and generally contain both metals and nonmetals
• Naming involves identifying the ions and then naming the compound based on the ions present
• The cation (positive ion) is named first, followed by the anion (negative ion)
• For monatomic cations, the name is the same as the element (e.g., Na+ is sodium)
• Monatomic anions are named by taking the root of the element name and adding "-ide" (e.g., Cl- is chloride)
• Example: NaCl is sodium chloride
• For metals that can form multiple ions (typically transition metals), a Roman numeral indicates the charge of the metal cation
• Example: Iron can form Fe2+ and Fe3+. FeCl2 is iron(II) chloride, and FeCl3 is iron(III) chloride
• An older method uses the suffixes "-ous" for the lower charge and "-ic" for the higher charge
• For example, Fe2+ is ferrous and Fe3+ is ferric. FeCl2 is ferrous chloride, and FeCl3 is ferric chloride
• This older system is less precise and less preferred, but still encountered

Naming Molecular Compounds

• Molecular compounds are formed by covalent bonds between nonmetals
• The more electropositive element is named first, followed by the more electronegative element (with an "-ide" ending)
• Prefixes are used to indicate the number of atoms of each element in the molecule
• Common prefixes include:
  • Mono- (1)
  • Di- (2)
  • Tri- (3)
  • Tetra- (4)
  • Penta- (5)
  • Hexa- (6)
  • Hepta- (7)
  • Octa- (8)
  • Nona- (9)
  • Deca- (10)
• The prefix "mono-" is usually omitted for the first element
• Examples:
  • CO is carbon monoxide
  • CO2 is carbon dioxide
  • N2O4 is dinitrogen tetroxide

Naming Acids

• Acids are compounds that produce H+ ions when dissolved in water
• Binary acids consist of hydrogen and one other element
• Named with the prefix "hydro-", followed by the root of the other element, and the suffix "-ic acid"
• Example: HCl(aq) is hydrochloric acid
• Oxyacids consist of hydrogen, oxygen, and another element
• If the polyatomic anion ends in "-ate", the acid is named with the suffix "-ic acid"
• If the polyatomic anion ends in "-ite", the acid is named with the suffix "-ous acid"
• Examples:
  • H2SO4 (sulfate) is sulfuric acid
  • H2SO3 (sulfite) is sulfurous acid
  • HNO3 (nitrate) is nitric acid
  • HNO2 (nitrite) is nitrous acid

Polyatomic Ions

• Polyatomic ions are ions composed of two or more atoms covalently bonded together and possessing an overall charge
• Common polyatomic ions include:
  • Ammonium (NH4+)
  • Hydroxide (OH-)
  • Nitrate (NO3-)
  • Nitrite (NO2-)
  • Sulfate (SO42-)
  • Sulfite (SO32-)
  • Phosphate (PO43-)
  • Carbonate (CO32-)
  • Acetate (C2H3O2- or CH3COO-)
  • Cyanide (CN-)
  • Permanganate (MnO4-)
  • Dichromate (Cr2O72-)
  • Chromate (CrO42-)
  • Hypochlorite (ClO-)
  • Chlorite (ClO2-)
  • Chlorate (ClO3-)
  • Perchlorate (ClO4-)
• These ions combine with other ions to form ionic compounds
• For example, sodium nitrate (NaNO3) is formed from sodium ions (Na+) and nitrate ions (NO3-)
• Calcium sulfate (CaSO4) is from calcium ions (Ca2+) and sulfate ions (SO42-)

Hydrates

• Hydrates are ionic compounds that have water molecules incorporated into their crystal structure
• Naming involves naming the ionic compound as usual, then adding "hydrate" with a prefix to indicate the number of water molecules
• Example: CuSO4·5H2O is copper(II) sulfate pentahydrate