elektron, the Greek word for "amber"

J.J. Thompson who was experimenting with Cathode Rays (more about that later) that had been discovered or first created by German scientist Johann Hittorf in 1869.

Reference to mass and location in the atom.

What is an Electron? Where are electrons to be found?

The spin in orbits around the nucleus of atoms. They do so in very specific orbits, often known as shells. Electrons fill the shells closest to the nucleus first before they fill the outer shells (generally this is true).

The periodic table can help you determine the number of electrons that can fit in each shell. Look at the number of element in each ROW (across) this is the number of electrons that fit in each shell (again useful but not really accurate).

The charge of the electron is opposite to the charge on the Proton and so it is attracted to it, however it is attracted to it but never quite gets to it, as they stay in shells.

The electron as the indivisible quantity of charge, there is no smaller amount of charge because there is no smaller particle with charge on it. The Charge on an electron is −1.602×10−19 C, so there are 6,241,509,647,120,417,390 electrons (6.24 x 1018) in 1 coulomb.

Electrons are not exactly heavy, they are quite light, in fact 9.109×10−31 kg.

Units of energy: eV, keV, MeV, GeV.


Why is work qV ? There is a force because a charge is trying to move through an electric field.

While voltage is not quite a distance, remember we said its a potential, like height, which is a distance.

We say the energy of an electron, is the work it would do in an electric field of 1 volt.

So the Work is the charge on the electron multiplied by the Voltage of the field.

1 eV = 1e- x 1 V

The charge on an electron (qe) = 1.602×10−19 C

1.602×10−19 C x 1 V

=> 1 eV = 1.602×10−19 J

1keV = 1000 eV = 1.602×10−16 J

1Mev = 1,000,000 eV = 1.602×10−13 J

1Gev = 1,000,000,000 eV = 1.602×10−10 J

You have to be able to convert from Joules to electronVolts and back again.

So how many eV is there in 3.6J ?

how many eV is there in 1 kWh ?

How many J is there in 48TeV ?

Electron named by G. J. Stoney.


George Johnstone Stoney (15 February 1826 – 5 July 1911) was an Irish physicist most famous for introducing the term electron as the "fundamental unit quantity of electricity". He had introduced the concept, though not the word, as early as 1874 and 1881, and the word came in 1891. He published around seventy-five scientific papers during his lifetime.

from wikipedia.org

Dr Johnstone Stoney was one of the most eminent scientific men that Ireland has produced and was also one who for many years took an important part in the educational development of the country as the Secretary of the Queen's University in Ireland, until the latter was superseded by the late Royal University. George Johnstone Stoney was born in February, 1826, and was the eldest son of Mr. George Stoney, of Oakley Park, King's County. The entered Trinity College, Dublin, and after a distinguished University career became the first regular Astronomical Assistant to the Earl of Rosse at the then recently established Observatory at Birr

The work to which he always attached most importance was that on the constitution of the sun and the development of molecular physics. His long memoir on solar physics is now regarded as a classic on the subject. His far-reaching explanations of the mode of escape of gases from planetory atmospheres has also received much support from recent writers. He showed that, when the temperature is high enough and the mass of the gaseous molecule small enough, then a molecule on the confines of the atmosphere of a planet will sometimes move with a velocity sufficient to carry it quite away from the attractive influence of planets below a certain mass. The gaseous atmosphere, therefore, of a planet, can only consist of molecules sufficiently heavy for that planet to retain them, or else the gas is still in process of leaking away from such a planet. Dr. Stoney thus explained the absence of atmosphere from our small moon, and was strongly of the opinion that helium is now escaping from the earth. Later on he foretold on this reasoning, that some considerable source of helium must exist on the earth when Sir William Ramsay discovered its presence on our planet. Helium was later on shown to be constantly supplied through hot springs, etc., and to be radioactive in origin.

At the Belfast meeting of the British Association in 1874 he showed that the real meaning of Faraday's laws of electrolysis is that electricity, like matter, consists of ultimately indivisible equal particles or atoms, and he suggested the name of " Electron " for these atoms--he further gave the first estimate of their electric quality. Stoney's name of " Electron " is now universally used, but the remarkable fact of their existence is often assumed to have been first shown by Von Helmholtz, who gave practically the same explanation of the electrolytic laws some years afterward in his Faraday Lecture of 1881.

Taken from The Daily Express, Thursday, July 6, 1911


Cathode Rays

The next thing that happened the Atom was not for almost 100 years, when J.J. Thompson who was experimenting with Cathode Rays (more about that later) that had been discovered or first created by German scientist Johann Hittorf in 1869. The cathode ray is also known as an electron beam, why? because it is a ray of electrons. However the rays were named before the electrons were named, that means they were found before the individual.

The Maltese Cross tube is one of the most famous Crookes tubes. The tube demonstrates that electrons go in a straight line and don't go through metal. The cross can actually lay down and

stand up (mechanically). When the cross lies down, the glass face of the tube emits a green glow when the electrons strike the glass wall, when it's right up you will see the shadow of the cross. After a while the glass gets "tired" and the glow is less strong, when the cross is tipped over at that time, the previous unexposed glass glows brighter than the surrounding glass. The tube shown is an early Pressler tube.

This phenomena was discovered by Johann Wilhelm Hittorf in 1869. (He was a former student of Julius Plücker) Hittorf did a lot of discharge research in the same period when Crookes did his discoveries, the scientists had many contacts and changed frequently information.

Particles of Cathode Rays

Like a wave:

  1. they travelled in straight lines
  2. Produced a shadow when obstructed by objects
  3. could pass through thin metal foils without disturbing them (Tested by New Zealander Ernest Rutherford using gold foil.)

These conflicting properties caused disruptions when trying to classify it as a wave or particle. Crookes insisted it was a particle, whilst Hertz maintained it was a wave. The debate was resolved when an electric field was used to deflect the rays by J. J. Thomson. This evidence that the beams were composed of particles was strong because scientists knew it was impossible to deflect electromagnetic waves with an electric field.

J.J. Thompson carried out 3 experiments he wanted to find different solutions to the following problems

1 Was negative charge seperable from the cathode beam.

"This experiment shows that however we twist and deflect the cathode rays by magnetic forces, the negative electrification follows the same path as the rays, and that this negative electrification is indissolubly connected with the cathode rays" J.J. Thompson

2 We know they are deflected in a magnetic field, can they be deflected in an electric field

Yes they did, and with what was decided a Negative charge.

3 Lets try to measure the Mass to Charge ratio.

He compared the deflection of his cathode rays to hydrogen ions, he found that they were not as forcefu as the hydrogen ions. In fact they were over a 1000 times greater than the mass to charge ratio of the Hydrogen, this means the particle is over 1000 time more charged or less than 1/1000th the mass?

This last experiment was carried out in 1897, J.J. Thompson had discovered negatively charged particles that were very small parts of the atom. The idea of these particles existing had be forwarded by an Irish man by the name of George Johnstone Stoney, he had called these particles Electrons, and so the name stuck.

The new idea was that these electrons were stuck in the atom randomly like raisins in a christmas cake.

Quantity of charge measured by Millikan.


A Simulation of the experiment in Java of the Oil drop Experiment

While you watch this experiment, take a quick count everytime you increase the Energy,

Energy Falling ones Rising ones

This table has been truncated you will probably need a lot more rows!