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Atoms tend to lose or gain electrons to form a full outer shell.

An ion is a charged particle. They are formed when atoms gain or lose electrons to form a full outer shell. Ions are charged because the number of protons is different from the number of electrons.

A molecular ion is a particle made of more than one atom that has an overall positive or negative charge.

• A negative ion is called an anion.
• A position ion is called a cation.

Simple ions have full outer shells, and the stable electronic configuration of the noble gases.