An atom is a unit of matter that is made up of protons, electrons and neutrons.
All matter is made up of atoms. They are the smallest particles of an element and represent the most basic units of matter. Atoms are so small that they cannot be seen, even with a microscope.
At the centre of the atom lies a structure called the nucleus, composed of protons and neutrons. The nucleus is positively charged due to the protons. The majority of the atomic mass is in the nucleus.
Electrons surround the nucleus and orbit it in layers known as electron shells. The electrons have a negative charge and almost no mass.
The overall charge of an atom is neutral. This is due to atoms having the same number of electrons and protons.