Everything in the world is made of atoms. So, it is important for scientists to try to understand exactly what atoms themselves are made of.
Atoms are made from three smaller sub-atomic particles:
Electrons - are very light particles that orbit around the nucleus at the center of the atom, in layers called energy levels or shells. The electrons are the black particles in the diagram above.
Protons - are found inside the nucleus of the atom. The protons are the red particles shown in the diagram. The nucleus is the center of the atom.
Neutrons - are also found inside the nucleus of the atom. The neutrons are shown by the blue colour in the diagram above.
The atomic number of each element tells us the number of protons that each atom of the element contains. For example, the element sodium has the atomic number of 11 and therefore has 11 protons in its nucleus.