The electron is by far the least massive of these particles with a negative electrical charge and a size that is too small to be measured using available techniques.
Protons have a positive charge and a mass 1,836 times that of the electron. The number of protons in an atom is called its atomic number.
Neutrons have no electrical charge and have a free mass of 1,839 times the mass of the electron. Neutrons are the heaviest of the three constituent particles, but their mass can be reduced by the nuclear binding energy. Neutrons and protons (collectively known as nucleons) have comparable dimensions. The neutron was discovered in 1932 by the English physicist James Chadwick.
If an atom has an equal number of protons and electrons, its net charge is 0. If it gains an extra electron, it becomes negatively charged and is known as an anion. If it loses an electron, it becomes positively charged and is known as a cation.