Atoms are the basic building blocks of ordinary matter. Atoms can join together to form molecules, which in turn form most of the objects around you.
Atoms are composed of particles called protons, electrons and neutrons. Protons carry a positive electrical charge, electrons carry a negative electrical charge and neutrons carry no electrical charge at all. The protons and neutrons cluster together in the central part of the atom, called the nucleus, and the electrons ‘orbit’ the nucleus. A particular atom will have the same number of protons and electrons and most atoms have at least as many neutrons as protons.
Protons and neutrons are both composed of other particles called quarks and gluons. Protons contain two ‘up’ quarks and one ‘down’ quark while neutrons contain one ‘up’ quark and two ‘down’ quarks. The gluons are responsible for binding the quarks to one another.