Leptons

The mass of the electron is about 1/1836 that of the proton. The electron has a negative charge and is thought to be a fundamental particle, meaning, that it has no further constituents. Every atom contains a nucleus (one or more protons and usually a similar number of neutrons, which are each composed of 3 quarks, these particular composite hadrons are known as baryons) and bound to it are one or more electrons. More than 99.4% of the mass of the atom is located in the nucleus. The protons carry positive charge, the neutrons carry no charge and the electron carries a negative charge. The electrons are attracted to the atomic nucleus by the electromagnetic force, while the protons and neutrons are bound by the strong nuclear force. If the number of protons and electrons are equal, than, the atom will be neutral. An atom is either electrically neutral or is known as an ion:

• Cation: positively charged ion.

• Anion: negatively charged ion.

Cations and anions, because of their unlike charge, can be bound into ionic compounds.

Electrons, like other quantum phenomenon, exhibit both wave and particle properties. The wavelike nature of the electron can be understood as an atomic orbital. This will be a mathematical function that will characterize the probability of locating an electron at a certain position when it is observed.

• The electron was discovered by J. J. Thomson.

• The muon was discovered by Carl D. Anderson.

• The tau was discovered by Martin Lewis Perl.