To indicate a more severe charge, the number of additional or missing electrons is supplied, as seen in (peroxide, negatively charged, polyatomic) and He²⁺ (alpha particle, positively charged, monatomic).

In the case of physical ionization in a fluid (gas or liquid), "ion pairs" are created by spontaneous molecule collisions, where each generated pair consists of a free electron and a positive ion. Ions are also created by chemical interactions, such