or elementary particle
Any of various self-contained units of matter or energy.
Discovery of the electron in 1897 and of the atomic nucleus in 1911 established that the atom is actually a composite of a cloud of electrons surrounding a tiny but heavy core. By the early 1930s it was found that the nucleus is composed of even smaller particles, called protons and neutrons . In the early 1970s it was discovered that these particles are made up of several types of even more basic units, named quarks , which, together with several types of leptons , constitute the fundamental building blocks of all matter. A third major group of subatomic particles consists of bosons , which transmit the forces of the universe. More than 200 subatomic particles have been detected so far, and most appear to have a corresponding antiparticle (see antimatter ).