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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.

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

Higher tier

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