Proton
- For alternative meanings see proton (disambiguation).
\n| Proton |
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| Classification |
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| Properties |
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\n\n| Mass: | 938 MeV | \n| Electric Charge: | 1.6 × 10-19 C | \n| Spin: | 1/2 | \n \n |
In
physics, the
proton is a
subatomic particle with a positive fundamental
electric charge of 1.6 × 10
-19 coulomb and a mass of 938
MeV (
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 aqueous solution (in other words, the
hydronium ion). In this context, a proton donor is an
acid and a proton acceptor a
base (see
acid-base reaction theories).
History
\nThe proton was discovered in 1918 by Ernest Rutherford. When investigating Nitrogen gas, he noticed that when alpha particles were shot into the gas, there were the signs of hydrogen noticed in the scintillation detectors. Rutherford worked out that the only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He therefore 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
\nProtons 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: particle physics, subatomic particle, neutron, proton-proton chain, proton pump inhibitor, list of particles.
External links
\n* Particle Data Group
Category:Nucleon
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