Neutrons, with protons and electrons, make up an atom. They are the particles in an atom that has a neutral charge. Neutrons and protons are found in the nucleus of an atom. Unlike protons, which have a positive charge, or electrons, which have a negative charge, neutrons have zero charges which mean they are neutral particles. They play a major role in the mass and radioactive properties of atoms. They bind with protons with the residual strong force. The attractive ‘strong’ force that holds the nucleus together affects both protons and neutrons in the same way.

Neutrons were predicted by Ernest Rutherford, and discovered by James Chadwick, in 1932. Atoms were fired at a thin pane of beryllium. Particles emerged which had no charge, and he called these ‘neutrons’. They were later added to the modern image of the atom.

Neutrons are present in almost all atomic nuclei except for Hydrogen. They have a mass of 1.675 × 10-24g, which is a little heavier than the proton. They are 1839 times heavier than electrons.

Atoms with the same number of protons in the nucleus, but different numbers of neutrons are referred to as isotopes of the same element. Like all hadrons, neutrons are made of quarks. A neutron is made of two down quarks and one up quark. One up quark has a charge of +2/3, and the two down quarks each have a charge of -1/3. The fact that these charges cancel out is why neutrons have a neutral (0) charge. Quarks are held together by gluons. The neutron is a baryon, which means it is a massive particle that is made up of 3 quarks (1 up quark and 2 down quarks). They are stable inside a nucleus. This structural stability is lost when neutrons are in a free, independent state.


Neutrons can be found in almost all atoms together with protons and electrons. Hydrogen-1 is the only exception. Atoms with the same number of protons but a different number of neutrons are called isotopes of the same element.

The number of neutrons in an atom does not affect its chemical properties. However, it affects its half-life, a measure of its stability. An unstable isotope has a short half-life, in which half of it decays to lighter elements.