Electric charge and conservation of charge

The basic constituents of matter, electrons and atomic nuclei, are all endowed with electric charge. It is through the electromagnetic fields generated by these charges that electrons and nuclei interact to form atoms and molecules and, hence, all materials. An electron carries a negative charge – e, and an atomic nucleus a positive charge Ze, where Z is an integer ranging from Z = 1 for hydrogen to Z = 92 for uranium (and higher for some unstable nuclei). The SI unit of charge is the coulomb (C) and e ≈ 1.602 × 10-19 C.

The assignation of negative and positive sign is no more than a convention, which was set in the eighteenth century by the American physicist and statesman Benjamin Franklin. It is, however, a profound law of nature that, in an isolated system, the net total charge will never change: charge is conserved. In much of physics and chemistry neither an electron nor an atomic nucleus is ever created or destroyed, and charge conservation follows from this. More generally, the processes of nuclear physics do create and annihilate electrons, and transmute nuclei, but no known physical process can change the net total charge of an isolated system.

Charge density

At the present limits of experimental resolution, electrons seem to be ‘point particles’, in the sense that no intrinsic size or structure has yet been discerned for them.