# Structure of the atom

An atom has a tiny nucleus of protons and neutrons, with electrons orbiting around it. Protons are positive, electrons negative and neutrons neutral.

Physics (school) · Part 08: Atoms and radioactivity · Card 1 of 8 · Last updated 2026-10-19

## Analogy

A tiny marble (nucleus) in the middle of a huge stadium, with electrons in the stands.

## Example

**Particle charges**

Proton: +1
Neutron: 0
Electron: -1
A neutral atom has equal
protons and electrons.

## In practice

An atom is mostly empty space. Its size is about 0.0000000001 m across.

## Practice

### Flashcards

- **What particles are in the nucleus?** Protons and neutrons.

## Questions people ask

### Why are atoms neutral overall?

A normal atom has the same number of protons as electrons. Each proton carries +1 charge and each electron -1, so the charges cancel exactly. If an atom gains or loses electrons it becomes charged and is called an ion.

### Where is most of an atom's mass?

Almost all of an atom's mass is in the nucleus. Protons and neutrons are each about 1,800 times heavier than an electron. The nucleus is tiny compared with the whole atom, so the atom is mostly empty space with a very dense centre.

## Related concepts

- [Atomic number and mass number](https://studyvisually.com/learn/science/physics-school/physics-school-part-8/physics-school-part-8-concept-2)
- [Nuclear fission](https://studyvisually.com/learn/science/physics-school/physics-school-part-8/physics-school-part-8-concept-7)
- [Nuclear fusion](https://studyvisually.com/learn/science/physics-school/physics-school-part-8/physics-school-part-8-concept-8)

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