Atoms that have net electric charges are called ions. Positive ions are called cations and negative ions are called anions.

Atoms have two types of charged particles:

• Protons have a positive charge and are found in the nucleus.
• Electrons have a negative charge and are found outside the nucleus. Electrons can be gained or lost.

Atoms are neutral if they have the same number of protons and electrons.

A cation forms when an atom loses one or more electrons. This results in it having more protons than electrons and therefore a net positive charge. Metals, which are in the groups on the left side and the center of the periodic table, lose electrons to form cations.

An anion forms when an atom gains one or more electrons. It now has more electrons than protons and therefore has a net negative charge. Nonmetallic elements gain electrons to form anions.