# Ion

An atom or group of atoms that has gained or lost electrons, so it carries an electrical charge. Losing electrons makes a positive ion. Gaining them makes a negative ion.

Chemistry (school) · Part 03: Bonding and structure · Card 1 of 9 · Last updated 2026-10-19

## Analogy

An ion is like a person who gave away or picked up a few coins. They are no longer balanced.

## Example

**Common ions**

Na: loses 1 -> Na+
Mg: loses 2 -> Mg2+
Cl: gains 1 -> Cl-
O: gains 2 -> O2-

## In practice

Sodium loses one electron to become Na+. Chlorine gains one to become Cl-.

## Practice

### Flashcards

- **What is the charge on an ion that has lost two electrons?** 2+
- **Why can ionic compounds conduct electricity when molten?** The ions are free to move and carry charge.

## Questions people ask

### Why do atoms form ions?

Atoms are more stable with a full outer shell of electrons. Metals reach this by losing their few outer electrons. Non-metals reach it by gaining a few. This is why sodium, with one outer electron, forms Na+ and chlorine, with seven, forms Cl-.

### How do you know the charge of an ion from its group?

Group 1 ions have a charge of 1+, group 2 ions 2+, group 6 ions 2- and group 7 ions 1-. Metals lose their outer electrons, so the group number gives the positive charge. Non-metals gain enough to reach eight, so subtract the group number from 8.

## Related concepts

- [Ionic lattice](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-3/chemistry-school-part-3-concept-5)

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