Ternary compound

In inorganic chemistry, a ternary compound is a compound containing three different elements. An example is sodium phosphate, Na₃PO₄. The sodium ion has a charge of 1+ and the phosphate ion has a charge of 3-. Therefore, three sodium ions are needed to balance the charge of one phosphate ion. Another example of a ternary compound is calcium carbonate, CaCO₃. In naming and writing the formulae for ternary compounds, rules are similar to binary compounds.

Sodium phosphate, Na₃PO₄, is a ternary compound.

According to Rustum Roy and Olaf Müller,[1] "the chemistry of the entire mineral world informs us that chemical complexity can easily be accommodated within structural simplicity." The example of zircon is cited, where various metal atoms are replaced in the same crystal structure. "The structural entity ... remains ternary in character and is able to accommodate an enormous range of chemical elements." The great variety of ternary compounds is therefore reduced to relatively few structures: "By dealing with approximately ten ternary structural groupings we can cover the most important structures of science and technology specific to the non-metallics world. It is a remarkable instance of nature's simplexity."[1]^:3,4

Letting A and B represent cations and X an anion, these ternary groupings are organized by stoichiometric types A₂BX₄, ABX₄, and ABX₃.

A ternary compound of type A₂BX₄ may be in the class of olivine, the spinel group, or phenakite. Examples include K₂NiF₄, β-K₂SO₄, and CaFe₂O₄.

One of type ABX₄ may be of the class of zircon, scheelite, barite or an ordered silicon dioxide derivative.

In the ABX₃ class of ternary compounds, there are the structures of perovskite (structure), calcium carbonate, pyroxenes, corundum and hexagonal ABX₂ types.[1]^{:figure 1,page 3}

Other ternary compounds are described as crystals of types ABX₂, A₂B₂X₇, ABX₅, A₂BX₆, and A₃BX₅.

In organic chemistry, the carbohydrates and carboxylic acids are ternary compounds with carbon, oxygen, and hydrogen. Other organic ternary compounds replace oxygen with another atom to form functional groups.

See also

• Binary compound
• Mitscherlich's law
• Tetranary compound

References

1. Rustum Roy & Olaf Müller (1974) The Major Ternary Structural Families, Springer-Verlag ISBN 9780387064307