and readily form ionic compounds. Ions consisting of only a single atom are termed monatomic ions, atomic ions or simple ions, while ions consisting of two or more atoms are termed polyatomic ions or molecular ions.

The net charge of an ion is indicated as a superscript on the right. To indicate a +1 or -1 charge, only a + or - is written respectively, as seen in Na⁺ (sodium ion) and (fluoride ion).