# Atom

The smallest piece of an element that still counts as that element. Everything around you is built from atoms.

Chemistry (school) · Part 01: Atoms and matter · Card 1 of 10 · Last updated 2026-10-19

## Analogy

Atoms are like Lego bricks. A few kinds of brick build a huge number of different models.

## In practice

A single drop of water holds billions of billions of atoms.

## Practice

### Flashcards

- **Why is a neutral atom neutral?** It has the same number of positive protons and negative electrons.

## Questions people ask

### How small is an atom?

An atom is about 0.0000000001 metres across, which is far too small to see with a normal microscope. About a million atoms placed side by side would stretch across the width of a human hair. Special machines can still image atoms.

### Can atoms be split?

Atoms can be split into protons, neutrons and electrons, but then they are no longer the same element. Splitting a nucleus, called nuclear fission, releases huge amounts of energy. Chemical reactions never split atoms. They only rearrange them into new groups.

## Related concepts

- [Proton](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-1/chemistry-school-part-1-concept-5)
- [Electron](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-1/chemistry-school-part-1-concept-7)

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