discovery of the electron

The Discovery Of The Electron The electron was discovered in 1895 by J.J. Thomson in the form of cathode rays, and was the first elementary particle to be identified. The electron is the lightest known particle which possesses an electric charge. Its rest mass is Me 9.1 x 10 -28 g, about 1/1836 of the mass of the proton or neutron. The charge of the electron is -e = -4.8 x 10^-10 esu and in many other decay processes. The electron itself is completely stable. Electrons contribute the bulk to ordinary matter; the volume of an atom is nearly all occupied by the cloud of elec trons surrounding the nucleus, which occupies only about 10^-13 of the atom's volume. The chemical properties of ordinary matter are determined by the electron cloud. The electron obeys the Fermi-Dirac statistics, and for this reason is often called a fermion. One of the primary attributes of matter, impenetrability, results from the fact that the elec tron, being a fermion, obeys the Pauli exclusion principle. The electron is the lightest of a family of elementary particles, the leptons. The other known charged leptons are the muon and the tau. These three particles differ only in mass; they have the same spin, charge, strong interactions, and weak interactions. In a weak interaction a charged lepton is either unchanged or changed into and uncharged lepton, that is a neutri no. In the latter case, each charged lepton is seen to change only into the corresponding neutrino. The electron has magnetic properties by virtue of (1) its orbital motion about the nucleus of its parent atom and (2) its rotation about its own axis. The magnetic properties are best described through the magnetic dipole movement associated with 1 and 2. The classical analog of the orbital magnetic dipole moment of a small current-carrying circuit. The electron spin magnetic dipole moment may be thought of as arising from the circulation of charge, that is, a current, about the electron axis; but a classical analog to this moment has much less meaning than that to the orbital magnetic dipole moment. The magnetic moments of the electrons in the atoms that make up a solid give rise to the bulk magnetism of the solid.