Proton
:''For alternative meanings see
proton (disambiguation).''
| Proton |
|---|
| Classification |
|
|
|
| Properties |
|
| Mass:
|
938 MeV/c2
|
| Electric Charge:
|
1.6 × 10−19 C
|
| Spin:
|
1/2
|
| Quark Composition:
|
1 Down, 2 Up
|
|
In
physics, the
proton (
Greek proton = first) is a
subatomic particle with a positive fundamental
electric charge of 1.6 × 10
−19 coulomb and a mass of 938 MeV/
c2 (
1.6726231 × 10−27 kg, or about 1800 times the mass of an
electron). The proton is observed to be stable, with a lower limit on its
half-life of about 10
35 years, although some theories predict that the
proton may decay.
The
nucleus of the most common isotope of the
hydrogen atom is a single proton. The nuclei of other atoms are composed of protons and
neutrons held together by the strong nuclear force. The number of protons in the nucleus determines the chemical properties of the atom and which
chemical element it is.
Protons are classified as
baryons and are composed of two Up
quarks and one Down quark, which are also held together by the strong nuclear force, mediated by
gluons. The proton's
antimatter equivalent is the
antiproton, which has the same magnitude charge as the proton but the opposite sign.
Because the electromagnetic force is many orders of magnitude stronger than the gravitational force, we see that the charge on the proton must be equal to the charge on the
electron, otherwise the net repulsion of having an excess of positive or negative charge (depending on which charge was numerically greater - atoms would not be electrically neutral) would cause a noticeable expansion effect on the universe, and indeed any gravitationally aggregated matter (planets, stars, etc.).
In
chemistry and
biochemistry, the term
proton may refer to the
hydrogen ion. In this context, a proton donor is an
acid and a proton acceptor a
base (see
acid-base reaction theories).
History
The proton was discovered in 1918 by Ernest Rutherford. He noticed that when alpha particles were shot into
nitrogen gas, his scintillation detectors showed the signatures of hydrogen nuclei. Rutherford determined that the only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He thus suggested that the hydrogen nucleus, which was known to have an atomic number of 1, was an elementary particle. This he named proton, from
protos, the Greek for "first".
Technological Applications
Protons can exist in spin states. This property is exploited by
nuclear magnetic resonance spectroscopy. In NMR spectroscopy, a magnetic field is applied to a substance in order to detect the shielding around the protons in the nuclei of that substance, which is provided by the surrounding electron clouds. Scientists can use this information to then construct the molecular structure of the molecule under study.
See also
External links
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Category:Nucleon