Cations are positively charged ions. An ion is an atom or group of atoms that does not have a neutral charge. The opposite of a cation is an anion, an ion with a negative charge.
An ion gains a positive or negative charge when it possesses an unequal number of protons and electrons. An ion with more protons than electrons is a positively-charged cation; an ion with more electrons than protons is a negatively-charged anion. Ions with opposing charges are attracted to one another. When a cation and an anion chemically bond, the resulting molecule is called an ionic compound.