All matter is made up of atoms. Most atoms have three parts: protons (positively charged), electrons (negatively charged), and neutrons (no charge).
Protons and neutrons are found in the centre of the atom, also called the nucleus.
Electrons move around the nucleus in clouds. The negative electrons are attracted to the positive nucleus with an electrical force similar to magnets. This is how the atom stays together.
Each atom of a same element has a defined number of protons in its nucleus. For instance, hydrogen has 1 proton, copper 29 protons and uranium 92 protons.
The periodic table ranks the elements according to the number of protons they have in their nucleus.
The number of neutrons for a same element can vary. Variations are called isotopes. For example, there are three types or isotopes of hydrogen:
- hydrogen-1 (one proton and no neutrons)
- hydrogen-2, which is called deuterium (one proton and one neutron)
- hydrogen-3, which is called tritium (one proton and two neutrons)
In most cases, an atom has the same number of protons and electrons.