Homoatomic Compounds

Homoatomic compounds are molecules formed by atoms of the same chemical element. They are also known as elemental molecules or allotropes when they represent different forms of the same element.

Nomenclature of Neutral Compounds

If it has more than one element, the prefixes di(2), tri(3), tetra(4), penta(5), hexa(6), hepta(7), octa(8), nona(9), deca(10), etc. are used.

• H₂: dihydrogen (molecular hydrogen)
• O₂: dioxygen (molecular oxygen)
• S₈: octasulfur
• P₄: tetraphosphorus
• He: helium (no prefix)

Cations (Positive Ions)

They are named like neutral compounds but their number and charge are indicated in parentheses. No space is left between the text and charge in parentheses.

• Na⁺: sodium(1+)
• Fe²⁺: iron(2+)
• Hg₂²⁺: dimercury(2+)
• Cu²⁺: copper(2+)
• Cu⁺: copper(1+)
• Mn²⁺: manganese(2+)

Anions (Negative Ions)

They are named similarly to cations with the difference that the suffix "ide" is added. Oxygen does not follow the rule and is called oxide.

• H⁻: hydride(1-)
• F⁻: fluoride(1-)
• Cl⁻: chloride(1-)
• Br⁻: bromide(1-)
• I⁻: iodide(1-)
• O²⁻: oxide(2-)
• S²⁻: sulfide(2-)
• Se²⁻: selenide(2-)
• Te²⁻: telluride(2-)
• N³⁻: nitride(3-)
• P³⁻: phosphide(3-)
• I₃⁻: triiodide(1-)
• O₂²⁻: dioxide(2-) (peroxide)
• N₃⁻: trinitride(1-) (azide)
• C₂²⁻: dicarbide(2-) (acetylide)
• O₂⁻: dioxide(1-) (superoxide)

Allotropy

Allotropy is the property of some chemical elements to exist in different forms with different molecular or crystalline structures. These forms are called allotropes.

For example, carbon can form different allotropes such as diamond, graphite, graphene, fullerenes, nanotubes, etc.

To name allotropes, another nomenclature has been developed.