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Essay Name       : 1147.txt 
Uploader         : 
Email Address    : gank@hotmail.com
Language         : english
Subject          : Chemistry
Title            : discovery of the electron
Grade            : b+
School System    : public
Country          : us
Author Comments  : i did this report for my chem 1 class, its nothing special, but if you need some info on electrons, or the discovery of, then this is great.
Teacher Comments : none
Date             : 11/17/96
Site found at    : link on another page (plowsky's i belive)
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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 <approximately 
equal>  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 <elec
trostatic unit). The sign of the electron's charge is negative by 
convention, and that of the equally charged proton is positive. 
This is somewhat a unfortunate convention, because the flow of 
electrons in a conductor is opposite to the conventional direc
tion of the current.

	The most accurate direct measurement of e is the oil drop 
experiment conducted by R.A. Milikan in 1909. In this experiment, 
the charges of droplets of oil in air are measured by finding the 
electric field which balances each drop against its weight. The 
weight of each drop is determined by observing its rate of free 
fall through the air, and using Stokes' formula for the viscous 
drag on a slowly moving sphere. The charges thus measured are 
integral multiples of e.

	Electrons are emitted in radioactivity <as beta rays> 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.
 
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