Compound Classification: Formulas and Names

Compound Classification

Overview of Compound Types

There are five primary types of compounds we will learn to name and write formulas for:

  • Binary Ionic: Compounds composed of two elements, with the first element being a metal.

  • Ternary Ionic: Compounds composed of three or more elements, always containing a polyatomic ion, with the first element being a metal or ammonium.

  • Binary Molecular: Compounds composed of two nonmetal elements.

  • Binary Acids: Acids formed from two elements, with hydrogen as the first element, and presented in an aqueous solution.

  • Ternary Acids: Acids formed from three or more elements, with hydrogen as the first element (part of a polyatomic ion), and presented in an aqueous solution.

Identifying Compound Type from a Formula

The initial step is to determine if the compound is binary (composed of 2 elements) or ternary (composed of 3 or more elements).

Binary Compounds (2 Elements)

To classify binary compounds, examine the first element:

  • If the first element is a metal: The compound is Binary Ionic.

  • If the first element is a nonmetal (excluding hydrogen): The compound is Binary Molecular.

  • If the first element is hydrogen:

    • If NOT aqueous (aq): Name it as a binary ionic compound.

    • If aqueous (aq): The compound is a Binary Acid.

Ternary Compounds (3 or More Elements)

Ternary compounds ALWAYS contain a polyatomic ion.

  • If the first element is a metal OR ammonium: The compound is Ternary Ionic.

  • If the first element is hydrogen:

    • If NOT aqueous (aq): Name it as a ternary ionic compound.

    • If aqueous (aq): The compound is a Ternary Acid.

Identifying Compound Type from a Chemical Name

When identifying compound types from a name, always focus on the first substance in the name.

  • If Ammonium is the first substance in the name: The compound is Ternary Ionic.

  • If a Metal is the first substance in the name: The compound is IONIC. To determine if it's binary or ternary, look at the second substance in the name:

    • If -ide is the suffix of the second substance: The compound is generally Binary Ionic.

    • EXCEPTIONS: The following are polyatomic ions with the -ide suffix. If the second substance is one of these, the compound is still ionic, but explicitly involves a polyatomic ion, thus making it potentially ternary depending on the overall composition (e.g., Sodium Hydroxide is NaOH, a ternary ionic compound despite the -ide suffix).

      • Peroxide

      • Hydroxide

      • Cyanide

  • If Hydrogen is the first substance in the name: It is an ionic compound, unless you are dealing with water (dihydrogen monoxide), which is a binary molecular compound.

  • If a Nonmetal is the first substance in the name: The compound is Binary Molecular.

  • If the word "Acid" is present in the name: It is an acid. To distinguish between binary and ternary acids:

    • If the acid has the prefix hydro-: It is a Binary Acid.

    • If the acid does not have the prefix hydro-: It is a Ternary Acid.