6.1 Elements and Their Ions
Compounds that contain ions are called ionic compounds. Ionic compounds generally form from metals and nonmetals. Compounds that do not contain ions, but instead consist of atoms bonded tightly together in molecules (uncharged groups of atoms that behave as a single unit), are called covalent compounds. Covalent compounds usually form from two nonmetals.
6.2 Writing Formulas of Ionic Compounds
Ionic compounds must be symbolized by a formula indicating the relative numbers of its constituent ions. These compounds must be electrically neutral. For instance, NaCl would be electrically neutral since it has a single Na+ ion and a single Cl- ion.
6.3 Naming Binary Compounds
Chemists use nomenclature rules to clearly name compounds. Ionic and molecular compounds are named using somewhat-different methods. Binary ionic compounds typically consist of a metal and a nonmetal. The name of the metal is written first, followed by the name of the nonmetal with its ending changed to –ide. For example, K2O is called potassium oxide. If the metal can form ions with different charges, a Roman numeral in parentheses follows the name of the metal to specify its charge. Thus, FeCl2 is iron(II) chloride and FeCl3 is iron(III) chloride.
Molecular compounds can form compounds with different ratios of their elements, so prefixes are used to specify the numbers of atoms of each element in a molecule of the compound. Examples include SF6, sulfur hexafluoride, and N2O4, dinitrogen tetroxide.
6.4 Naming Compounds Containing Polyatomic Ions
Some compounds contain polyatomic ions. For compounds with polyatomic ions, name the metal first, followed by the name of the polyatomic ion.
6.5 Naming Acids
Acids are an important class of compounds containing hydrogen and having special nomenclature rules. Binary acids are named using the prefix hydro-, changing the –ide suffix to –ic, and adding “acid;” HCl is hydrochloric acid. Oxyacids are named by changing the ending of the anion to –ic, and adding “acid;” H2CO3 is carbonic acid.
Attribution & References
Except where otherwise noted, this page is adapted by Adrienne Richards from “2.6 Ionic and Molecular Compounds Summary” and “2.7 Chemical Nomenclature Summary” In Chemistry 2e (OpenStax) by Paul Flowers, Klaus Theopold, Richard Langley, & William R. Robinson, licensed under CC BY 4.0. Access for free at Chemistry 2e (OpenStax).