The neutron is a subatomic particle found in the nucleus of the atom and has no charge. The number of neutrons in the nucleus is different for different elements. In some cases, the number of neutrons can vary within atoms of the same element.
For instance, the normal hydrogen atom does not have neutrons in the nucleus. However, the isotopes of hydrogen, deuterium and tritium, have neutrons in the nucleus. Deuterium has one neutron, while tritium has two neutrons in the nucleus.
Neutrons were discovered by James Chadwick in 1932. The mass of a neutron is 1.675 × 10^-24g, and it is 1,839 times heavier than an electron. Some atoms, such as uranium atoms, have many neutrons in the nucleus, which makes them heavy and unstable.