Protons: Definition, Charge & Mass

Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

Protons can be found in the nucleus of every atom. While originally it had been thought that protons were a fundamental particle, recent research has shown that protons are made of quarks. This lesson will cover the properties of the proton.


A proton is a subatomic particle with a positive electric charge. Protons are found in the nucleus of every atom. In fact, the number of protons in each atom is it's atomic number.

The atomic number is equal to the number of protons in the nucleus

Until recently, the proton was considered a fundamental particle. However, new technologies have led to the discovery that the proton is actually composed of smaller particles called quarks. A quark is a fundamental particle of matter that only recently has been discovered. There are six known types of quarks; up, down, strange, charm, top and bottom. A proton is composed of two up quarks and one down quark.

Quark makeup of a proton

A proton can be formed as the result of an unstable neutron. After about 900 seconds away from a nucleus, a neutron will break down radioactively into a proton, electron and an anti-neutrino. Unlike a neutron, a free proton is stable. When free protons interact with each other, they form hydrogen molecules. Our sun, along with most other stars in the universe, are primarily composed of hydrogen.


Protons have a charge of +1 elementary charge. An elementary charge is denoted by the letter e and was originated in 1874 by George Stoney. While a proton has a charge of +1 or 1e, an electron has a charge of -1 or -e and a neutron has no charge or 0e.

1 elementary charge is equal to:

  • 1.602 x 10^-19 Coulombs
  • 4.80320425*10^-10 Statcoulombs

A coulomb is a type of unit of electric charge and is equivalent of one ampere being steadily transported per one second. A statcoulomb is a unit of electric charge in the centimeter-gram-second system of units (cgs) and Gaussian units.


The mass of a proton is extremely small when put in human sized units. The mass of one proton is 1.67 x 10-27 kg. Another common unit of measuring the mass of a proton is the electronvolt, in this unit a proton has a mass of 938 MeV/c^2. In chemistry, moles are a common form of measurement. Using this form of measurement, 1 mole (6.022 x 10^23) of hydrogen atoms will give a mass of 1 gram.

Although extremely small when compared to items we feel and touch, a proton has the mass of approximately 1,836 electrons. It's all relative.

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