Thus, the electron cloud determinesįigure 1. Some of the electrons in a typical atom can be quite close to the nucleus, while others can be at distances which are many thousands of times larger than the diameter of the nucleus. They move very rapidly about the nucleus in orbits which have very definite energies, forming a sort of electron cloud around it. The electrons are held in the atom by the attractive force exerted on them by the positively charged nucleus. The atom is electrically neutral and thus the positive electrical charge on the nucleus has the same magnitude as the negative charge due to all the electrons. The mass of the electron is small even by atomic standards and has the value 9.109389 × 10 -31 kg (0.5110 M V/c 2 e, being only about 1/1836 the mass of the proton.Īll atoms found in nature have a positively charged nucleus about which the negatively charged electrons move.

The magnitude of this charge, usually designated by e, has been measured very precisely and is 1.602177 × 10 -19 coulombs. However, scientists have never been able to observe an isolated quark, so for all practical purposes the charge on the electron can still be considered the fundamental unit of charge found in nature. For example, the neutrons and protons, which make up the nuclei of atoms, are baryons. Recently, however, considerable evidence has been found to indicate that particles classified as mesons and baryons are made up of objects called quarks, which have charges of either 2/3 or 1/3 the charge on the electron. All electrical charges were believed to be integral multiples of this charge. The size of the charge on the electron has for many years been considered the fundamental unit of charge found in nature. The electron is fundamental, in that it is not believed to be made up of smaller constituents.

The electron is a negatively charged subatomic particle which is an important component of the atoms which make up ordinary matter.

Charge of electron