'''Helium atom''' (schematic)
Showing two protons (red), two neutrons (green) and two electrons (yellow).
In
physics or
chemistry, a
subatomic particle is a particle smaller than an
atom. These include atomic constituents such as
electrons,
protons, and
neutrons (protons and neutrons are actually composite particles, made up of
quarks), as well as particles produced by radiative and scattering processes, such as
photons,
neutrinos, and
muons. Most of the particles that have been discovered and studied are not encountered under normal earth conditions; they have to be produced during scattering processes in
particle accelerators. The study of subatomic particles is the most active branch of
particle physics.
Subatomic particles found in atoms
The only subatomic particles found in ordinary atoms are the electron, proton and neutron. The space (or
orbital(s)) containing the electron (symbol
e- ), or electrons, makes up the bulk of an atom's volume. The configuration (and consequently the behaviour) of the electron(s) is responsible for the
chemistry of atoms; an electron has 1/1836 the mass of a
hydrogen atom and a negative charge. Protons (symbol
p+ ) are found in atomic
nuclei; a proton is about the same mass as a
hydrogen atom and carries a positive charge equal in magnitude but opposite in sign to an electron. Neutrons (symbol
n) are also found in nuclei and are responsible for differing
isotopes of atoms; neutrons are electrically neutral and have slightly greater mass than protons. The proton and neutron are both composed of two kinds of elementary subatomic particles: the up and down quarks (symbols
u and
d).
Other subatomic particles
Hadrons are particles composed of
quarks. They are divided into two classes: baryons and mesons.
Baryons are composed of three quarks and have a large rest mass for subatomic particles. The
proton and
neutron are the only stable baryons (and the neutron is only stable inside atomic nuclei). Every baryon has an
antiparticle composed of three antiquarks.
Mesons are composed of a normal quark and an antiquark, which gives them
baryon number zero. There are no stable mesons; the most stable have half lives on the order of nanoseconds. They have a rest mass starting with 140 MeV for the lightest mesons, the
pion. The antiparticles of mesons are other mesons.
Leptons are not composed of quarks, but are elementary particles (no smaller constituent is currently known). The only known leptons are
electrons,
muons,
tauons and
neutrinos. Until recently neutrinos were thought to have zero rest mass; their masses are much smaller than the masses of any other subatomic particles. In addition to the electron, all three types of neutrino are stable. Each lepton also has an antiparticle.
See also
External links
References
Recent News
Category:Quantum mechanics
da:Subatomar partikel
de:Subatomaren Elementarteilchen
ja:素粒子
hu:Szubatomi részecske
pt:Partículas
he:חלקיק תת-אטומי
sk:Subatomárna častica