Structure of the atom
Nucleus and shells
An atom has a central The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei.. This is surrounded by Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons. arranged in shells.
The nucleus is tiny compared to the atom as a whole:
- the radius of an atom is about 0.1 nm (1 × 10-10 m)
- the radius of a nucleus (1 × 10-14 m) is less than \(\frac{1}{10,000}\) of the radius of an atom
For comparison, the radius of a typical bacterium is 1 × 10-6 m and the radius of a human hair is about 1 × 10-4 m.
Learn more on atomic structure in this podcast.
Listen to the full series on BBC Sounds.
Subatomic particles
The nuclei of all atoms contain subatomic particles called Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1.. The nuclei of most atoms also contain Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0..
The The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of subatomic particles are very tiny. Instead of writing their actual masses in kilograms, we often use their The relative mass is the number of times heavier a particle is, compared to another.. The relative mass of a proton is 1, and a particle with a relative mass smaller than 1 has less mass.
| Subatomic particle | Relative mass | Relative charge |
| Proton | 1 | +1 |
| Neutron | 1 | 0 |
| Electron | Very small | -1 |
| Subatomic particle | Proton |
|---|---|
| Relative mass | 1 |
| Relative charge | +1 |
| Subatomic particle | Neutron |
|---|---|
| Relative mass | 1 |
| Relative charge | 0 |
| Subatomic particle | Electron |
|---|---|
| Relative mass | Very small |
| Relative charge | -1 |
The mass of an electron is very small compared to a proton or a neutron. Since the nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus.
Protons and electrons have electrical charges that are equal and opposite.