An ion is an atom or group of atoms that has lost or gained one or more electrons. This produces a charged particle, which can be either positive or negative.

Normally, an atom is neutrally charged. When negatively charged electrons are lost from an atom the resultant ion is positively charged and it is called a cation. An ion that has gained electrons is negatively charged and called an anion. The name ion comes from the Greek ienai, meaning to go. This is related to their behavior during electrolysis where the ions move to the two opposite electrodes. Properties of ions are generally very different from the atoms from which they are derived.

The net charge on an ion is denoted by a superscript showing both the size and charge. A cation can have +1, +2, or +3, these cases are brought about by the loss of one, two, or three...