Atomic structure
This section describes the The scientific idea that an atom has electrons surrounding a nucleus that contains protons and neutrons. of an All elements are made of atoms. An atom consists of a nucleus containing protons and neutrons, surrounded by electrons..
The nuclear model
Atoms contain three sub-atomic particles called Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1., Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0. and Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. The protons and neutrons are found in the 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. at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in energy levels around the nucleus.
The table shows the The characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point. of these three sub-atomic particles.
| Particle | Relative mass | Relative charge |
| Proton | 1 | +1 |
| Neutron | 1 | 0 |
| Electron | Almost zero | –1 |
| Particle | Proton |
|---|---|
| Relative mass | 1 |
| Relative charge | +1 |
| Particle | Neutron |
|---|---|
| Relative mass | 1 |
| Relative charge | 0 |
| Particle | Electron |
|---|---|
| Relative mass | Almost zero |
| Relative charge | –1 |
The number of electrons in an atom is always the same as the number of protons, so atoms are electrically An object that does not have a positive or negative charge. overall. Atoms can lose or gain electrons. When they do, they form charged particles called ions:
- if an atom loses one or more electrons, it becomes a positively charged ion
- if an atom gains one or more electrons, it becomes a negatively charged ion