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Introduction to Ternary Compounds

In chemistry, a compound which contains three different elements is termed as ternary compound. An example of ternary compound is sodium phosphate, Na3PO4. The sodium ion exhibit a charge of 1+ and the phosphate ion exhibit a charge of 3-. Therefore, three sodium ions are required to balance the charge of one phosphate ion. Another example is Sodium Chlorate (NaClO3), which has: -Sodium (Na) -Chlorine (Cl) -Oxygen (O).

The most common types of ternary compounds are metallic cation (positive ion) and polyatomic anion (negative ion).   The only commonly used polyatomic ion with a positive charge is the ammonium ion.

Rules for Naming Ternary Compounds:

1)     Decide whether the metal is a metal with fixed ionic charge or variable charge.

2)     Name the metal, following the rules in naming for:

  • Metal having fixed ionic charge, or
  • Metal having variable charge.

3)     Name the polyatomic anion subsequent the name of the metal.

4)     No Greek prefixes necessary here as the metal charge is either implicitly or explicitly specified and, hence, in forming a compound, there is only one possible combination with the polyatomic anion.

5)     For compounds containing NH4+ cations:

  • Name the cation first followed by the anion.

Examples of Ternary Compounds:

For writing the proper chemical formula of potassium hydroxide.

Step 1:- Write the symbols for the monatomic and polyatomic ions in the compound.  Potassium = K      Hydroxide = OH

Step 2:- See the oxidation numbers of the ions involved and write them as superscripts to the right of the elemental symbols.

Potassium = K+     Hydroxide = OH-

Step 3:- Use the right combination of ions to produce a compound having a net charge of zero. Parenthesis must be used more than one of a polyatomic ion is used.  For this case, (+1) + (-1) = 0.  Therefore, only one of each ion is used.  No subscripts are compulsory.  If more than one hydroxide ion is required, it would be put in parenthesis with the subscript on the outside.