Naming Rules: Ionic vs Molecular Compounds and Acids

Ionic vs molecular compounds

  • Ionic compounds contain a metal cation (or ammonium); molecular compounds consist of only nonmetals.
  • Ionic compounds require balancing charges to form a neutral formula; molecular compounds do not involve balancing charges.
  • The formula of ionic compounds reflects charge balancing; molecular formulas reflect the actual number of atoms.

Naming patterns for molecular compounds

  • Molecular naming uses prefixes to indicate how many atoms of each element are present.
  • Prefix rules:
    • Do not use mono for the first element.
    • If mono would be the second element, you must use it (e.g., monoxide).
    • If di, tri, tetra, etc. are used, they must appear regardless of position.
  • These conventions yield names that match the formula for simple covalent compounds.

Acids: overview of patterns

  • Acids without metals follow two main naming patterns: hydrohalic acids and oxoacids.
  • Hydrohalic acids use a hydro-based prefix with an -ic ending derived from the halogen name; oxoacids are named from polyatomic ions and do not use hydro.

Hydrohalic acids

  • Pattern: hydro + halogen stem + ic
  • Examples:
    • extF<br/>ightarrowexthydrofluoricacidext{F} <br /> ightarrow ext{hydrofluoric acid}
    • extCl<br/>ightarrowexthydrochloricacidext{Cl} <br /> ightarrow ext{hydrochloric acid}
    • extBr<br/>ightarrowexthydrobromicacidext{Br} <br /> ightarrow ext{hydrobromic acid}
    • extI<br/>ightarrowexthydroiodicacidext{I} <br /> ightarrow ext{hydroiodic acid}
  • Note: You replace the last syllable of the halogen name with "ic" and add the prefix "hydro".

Oxoacids

  • Pattern: names depend on the polyatomic anion; no "hydro" prefix.
  • Rules for the anion name:
    • -ate becomes -ic
    • -ite becomes -ous
  • Examples:
    • Perchlorate ion ClO4−\mathrm{ClO_4^-} → perchloric acid
    • Chlorite ion ClO2−\mathrm{ClO_2^-} → chlorous acid

Quick references

  • Oxoacids derive from polyatomic ions (-ate/-ite forms).
  • Hydroelements pattern applies only to hydrohalic acids.

Scope note

  • These rules cover common acids and simple molecular compounds; larger organic compounds require different naming conventions not covered here.