Table of Common Ions

Common Ions

The names of compounds of the metal ions in this table do not use the "Stock system" (i.e., Roman numerals to indicate the charge on the metal). For all other metals, the Stock system is required in the name of the compound (but you may not use Roman numerals in the formula).

IIA

IIIB

IVB

VIB

VIIB

VIIIB

IIB

IIIA

IVA

VIA

VIIA

VIIIA

Li⁺

Be²⁺

C^4–

N^3–

O^2–

F^–

Na⁺

Mg²⁺

Al³⁺

Si^4–

P^3–

S^2–

Cl^–

K⁺

Ca²⁺

Zn²⁺

Ga³⁺

As^3–

Se^2–

Br^–

Rb⁺

Sr²⁺

Ag⁺

Cd²⁺

Te^2–

I^–

Cs⁺

Ba²⁺

At^–

Fr⁺

Ra²⁺

The Stock system is used for all metal ions not listed in this table that combine with nonmetals, metalloids, or polyatomic ions in ionic compounds. In the Stock system, a Roman numeral is used in the name of the compound (not in the formula) to indicate the charge on the metal ion in an ionic compound only if the metal can have two or more charges (i.e., if the metal ion is not one of the ions listed in the above table).

The charges on the alkali metals, alkaline earth metals, and aluminum in ionic compounds are fixed, with extremely few exceptions in isolated research projects, etc.

The charges on silver, cadmium, zinc, and gallium are typically those which are shown above, so many books omit the Roman numeral for these as well. In my classes, use of the Stock system on these four elements is optional.

I have also listed the nonmetals in this table, because in most cases, their ions also have consistent charges when they are in ionic compounds. Remember: When nonmetals are in covalent compounds (bonding with other nonmetals), they don't have charges at all because they are sharing electrons, and are not ions.

Note that metalloids are typically named as if they were nonmetals.

Hydrogen is H ⁺ when combined with nonmetals in acids and is H ^– when combined with metals in ionic compounds.