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2.7 Chemical Nomenclature - rules for naming . . . . composed of a cation and an anion
metal + nonmetal and . . . . composed of two non-metals. compounds.

Naming Ionic Compounds

1. List the cation's name first.
2. List the anion's name last. NaCl is sodium chloride.
3. Do not use Greek prefixes (di-, tri-, etc.). CaF₂ is Calcium fluoride . . .not Calcium difluoride. For ionic compounds, knowing the cation's and anion's charge is all that is needed to write the ionic formula.
4. For transition metal cations, write the charge using Roman numerals after the element's name. FeCl₃ is Iron(III) chloride. When speaking the name of FeCl₂ and FeCl₃, one would say "Iron two chloride" and "Iron three chloride", respectively.
5. Hydrates are named by listing the ionic compound first followed by a Greek prefix and the word "hydrate". CuSO₄•5H₂O is Copper(II) sulfate pentahydrate. The Greek prefixes are
   • mono-
   • di-
   • tri-
   • tetra-
   • penta-
   • hexa-
   • hepta-
   • octa-
   • nona-
   • deca-

Naming Molecular Compounds

Molecular compounds are composed of two non-metals (or a metalloid and a metal). Consider the three oxides of nitrogen: NO₂, N₂O₄ and N₂O₅ . . . . if you were asked to write "Nitrogen oxide", which compound would you write. It turns out that there isn't a way to know unless Greek prefixes are used.

• NO₂ is named nitrogen dioxide.
• N₂O₄ is named dinitrogen tetroxide*.
• N₂O₅ is named dinitrogen pentoxide*.

* if the second name begins with a vowel, the ending vowel in the Greek prefix ("mono", "tetra", "penta", "hexa", etc.) is omitted.

Naming Acids

Acids are formed when the cation H⁺ combines with an anion. The importance of acids in chemistry and chemical reactions is significant . . . . the most common acids are:

• HCl - hydrochloric acid
• HC₂H₃O₂ - acetic acid
• HNO₃ - nitric acid
• H₂SO₄ - sulfuric acid
• H₃PO₄ - phosphoric acid