- The particles of the nucleus are held together by a force called the strong nuclear force.
- The nucleus is made from particles called protons and neutrons which are made of even smaller particles called quarks.
- Electrons are held to the nucleus by electrical charge because they have an opposite electrical charge to the protons in the nucleus.
- Electrons behave as if they were stacked arround the nucleus in different levels called shells.
- There is a certain number of electrons in each shell.