proton

American  

[proh-ton] / ˈproʊ tɒn /

noun

Physics, Chemistry.

1. a positively charged elementary particle that is a fundamental constituent of all atomic nuclei. It is the lightest and most stable baryon, having a charge equal in magnitude to that of the electron, a spin of ½, and a mass of 1.673 × 10 -27 kg. P

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proton British  

/ ˈprəʊtɒn /

noun

1. a stable, positively charged elementary particle, found in atomic nuclei in numbers equal to the atomic number of the element. It is a baryon with a charge of 1.602176462 × 10 ^–19 coulomb, a rest mass of 1.672 62159 × 10 ^–27 kilogram, and spin 1/ 2

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proton Scientific  

/ prō′tŏn′ /

1. A stable subatomic particle in the baryon family having a mass of 1.672 × 10 ^{- 24} grams (1,836 times that of the electron) and a positive electric charge of approximately 1.602 × 10 ^{- 19} coulombs. Protons make up part of the nucleus of all atoms except hydrogen, whose nucleus consists of a single proton. In neutral atoms, the number of protons is the same as the number of electrons. In positively charged atoms, the number of protons is greater than the number of electrons, and in negatively charged atoms electrons outnumber protons. Protons are believed to be composed of two up quarks and one down quark.

2. See Table at subatomic particle

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proton Cultural  

1. An elementary particle with a positive charge, found in the nucleus of an atom.

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Discover More

Protons and neutrons make up most of an atom's mass.

A proton is over a thousand times heavier than an electron.

Other Word Forms

• protonic adjective

Etymology

Origin of proton

Term first suggested in 1920 by English physicist Ernest Rutherford as noun use of Greek prôton, neuter of prôtos “first,” the proton being the constituent of hydrogen nuclei, and formed on the analogy of electron; see first, electron

Compare meaning

How does proton compare to similar and commonly confused words? Explore the most common comparisons:

• proton vs. electron

Explanation

Atoms are made up of three main particles: protons, electrons, and neutrons. A proton has a positive electrical charge, while electrons are negative. The number of protons and electrons is equal in each atom. The atomic number of an element, which is the number in the upper left corner of its box on the periodic table, is the number of protons in each atom. The hydrogen atom, for example, has just one proton, so it also has one electron and its atomic number is 1. If you have an atom with two protons in its nucleus, you know it can't be a hydrogen atom.

Example Sentences

For the first time, researchers directly measured how arsenic-73 captures a proton to form selenium-74 using a rare isotope beam.

From Science Daily • Apr. 14, 2026

While a proton contains two up quarks and one down quark, the Ξcc⁺ replaces the up quarks with heavier charm quarks.

From Science Daily • Mar. 19, 2026

Scientists hope the particle -- which is similar to a proton but four times heavier -- will reveal more about the strange behaviour of quantum mechanics.

From Barron's • Mar. 17, 2026

The centre in London is huge, with a vast cyclotron buried five stories underground and powering the proton beam 24 hours a day, Dr Hiley said.

From BBC • Mar. 11, 2026

A number of such experiments have been carried out, but none have yielded definite evidence of proton or neutron decay.

From "A Brief History of Time: And Other Essays" by Stephen Hawking