The nucleus of an atom contains positively charged particles called protons and particles with no charge called neutrons.

The number of protons of an atom determines its atomic number, while the number of protons and neutrons make up its atomic mass.

The atomic number determines chemical properties of elements such as hydrogen and carbon.

Electrons are negatively charged particles and orbit the nucleus in energy shells.

Atoms are electrically neutral: they always have an equal number of protons and electrons.