Ions can be creatit bi baith chemical an pheesical means. In chemical terms, if a neutral atom loses ane or mair electrons, it haes a net positive charge an is kent as a cation. If an atom gains electrons, it haes a net negative charge an is kent as an anion. An ion consistin o a single atom is an atomic or monatomic ion; if it consists o twa or mair atoms, it is a molecular or polyatomic ion.
In the case o pheesical ionization o a medium, such as a gas, whit are kent as "ion pairs" are creatit bi ion impact, an each pair consists o a free electron an a positive ion.