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Chapter 8: The Electron Shows the Way


The word atom comes from the Greek tomos, to cut, and a meaning not, because it was thought that atoms could not be split up. But it was later found that atoms could be split up, with electrons being the first part found, by J J Thomson in 1897 at the Cavendish Laboratory at Cambridge University (while Ernest Rutherford was there working with him).


  • Are a sub atomic particle.
  • Orbit the nucleus of an atom.
  • Are really really tiny and very very light weight (a mass of 9.11 * 10-31 kg).
  • Negatively charged.

The last attribute is important because a flow of electrons is electricity. Without electrons we wouldn't have electric lights (so we'd have candle-lit dinners much more often), heaters (so more homes would have fireplaces), motors (so we'd have to wash all our clothes by hand), etc.

Each electron orbits at a particular energy level. Electrons can be excited into higher energy levels when they absorb a photon (a packet of light), or they can fall into a lower energy level by emitting a photon. The photon emitted has the energy that was needed to be lost for the electron to drop into the lower energy level, which means the photon will have a particular wavelength or colour. This is how spectral lines are made. The difference between the particular energy levels the electron is jumping between determines the energy of the photon given off, and thus the colour of the light emitted. This is how sodium has a strong pair of yellow-orange spectral lines, and why neon signs glow red.

Electron beams are used in CRTs (see below), welding, lithography, and electron microscopes.


The most common type of radiometer in the home is the Crookes radiometer, named after Sir William Crookes who invented it in 1873.

From Wikipedia:

The radiometer is made from a glass bulb from which much of the air has been removed to form a partial vacuum. Inside the bulb, on a low friction spindle, is a rotor with several (usually four) vertical lightweight metal vanes spaced equally around the axis. The vanes are polished or white on one side, black on the other. When exposed to sunlight, artificial light, or infrared radiation (even the heat of a hand nearby can be enough), the vanes turn with no apparent motive power, the dark sides retreating from the radiation source and the light sides advancing. Cooling the radiometer causes rotation in the opposite direction.


Although it has the word-element "meter" in its title, a Crookes radiometer does not quantitatively measure anything by itself. A measurement of the speed of its rotation can, however, be obtained using a spinning slotted disk, which functions as a simple stroboscope.


In 1901, with a better vacuum pump, Pyotr Lebedev showed that in fact, the radiometer only works when there is low pressure gas in the bulb, and the vanes stay motionless in a hard vacuum.

So it's important that most of the air is removed so that air resistance doesn't slow the vanes down much, but it's also important that there is a small amount of air left in so that the thing will still work.

The radiometer I demonstrated during the lesson was brought back to New Zealand by my older brother after a backpacking (yes, backpacking) trip around Germany. They should be available in New Zealand shops.


An oscilloscope is a device with a cathode ray tube (CRT) used for measuring the voltage of electrical signals and looking at the shape of wave forms, such as AC mains voltage or audio wave forms (like a person's voice or music).

Cathode ray tubes are basically the working bit of most televisions and computer monitors - the picture tube. They got their name from how the beam of electrons in them that makes the "picture" was produced. The electron beam is released by the cathode at the back of the CRT.

A big step forward came in 1946 when two men invented the triggering oscilloscope, which has its trace triggered when the voltage is at a certain amount. This means the trace on the screen will always be in the same place.

Ernest Rutherford

Lord Rutherford of Nelson is one of New Zealand's most famous scientists, born 30 August 1871 in Brightwater, near Nelson, New Zealand. He was the fourth child of twelve. He died 19 October 1937. In Auckland in 1925 he said "I have always been proud of the fact that I am a New Zealander."

He was known as the father of the nuclear age because he came up with the orbital model of the atom after firing alpha particles through gold foil and realising atoms were mostly empty space, and for being the first to split the atom (in 1917). Albert Einstein called him "a second Newton".

Some of Ernest Rutherford's many achievements:

  • In 1887 he won a scholarship to Nelson College then in 1889 won a scholarship to go to the University of New Zealand.
  • In 1892 he got a BA degree. "Mr Rutherford, BA."
  • In 1893 he invented a machine that could measure time differences of up to one hundred-thousandths of a second. With that machine (in his first year of research at university) he demonstrated that it was possible for iron to be magnetized by high frequency currents.
  • And in the same year got an MA with double First Class Honours. "Mr Rutherford, MA."
  • In 1894 he got a BSc in Chemistry and Geology. "Mr Rutherford, BSc, MA."
  • In 1895 he got a scholarship to study anywhere in the world, so until 1898 he was at the Cavendish Laboratory in Cambridge, England, where he briefly held the world record (in 1896) for the distance over which electromagnetic waves could be detected.
  • In 1898 he found radioactive rays are two main types, and came up with the terms alpha and beta radiation.
  • In 1898 Rutherford was appointed as Professor of physics at McGill University, in Canada.
  • In 1899 he demonstrated the principle which is the basis of the modern smoke detector, and also discovered the radioactive gas radon.
  • In 1901 he got a DSc from the University of New Zealand. "Dr Rutherford, DSc, BSc, MA."
  • While there he demonstrated that radioactivity was the spontaneous disintegration of atoms and discovered a radioactive substance has a half life.
  • Also while there he invented a device for measuring vibrations caused by streetcars and one for allowing trains to signal to stations using wireless telegraphy.
  • In 1904 he was awarded the Rumford Medal.
  • In 1907 he went back to England, to take up the position of Professor of Physics at Manchester University.
  • In 1908 he invented the Rutherford-Geiger detector of single ionizing particles.
  • He won the 1908 Nobel Prize in Chemistry "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances." (In other words, what he discovered in Canada.) "Dr Rutherford, Nobel Laureate."
  • 1909 famous particle scattering experiment - "It was almost as incredible as if you fired a fifteen inch shell at a piece of tissue paper and it came back to hit you."
  • In 1911 announced the nuclear model of the atom.
  • He was knighted in 1914. "Sir Ernest Rutherford."
  • During World War I he worked on accoustic submarine detection.
  • In 1917 (not 1907 as Wikipedia says), and reported in 1919, he became the world's first successful alchemist, converting nitrogen into oxygen, thereby splitting the atom and ushering in the nuclear age.
  • In 1919 (Wikipedia says 1917) he returned to the Cavendish Laboratory as Director.
  • In 1920 he came up with the idea of neutrons, to help keep the positively charged nucleus of an atom together. (Neutrons were later discovered by James Chadwick, who for that won the 1935 Nobel Prize for Physics.)
  • In 1925 he was admitted to the Order of Merit (then limited to 24 living people).
  • In 1931 he was created Baron Rutherford of Nelson of Cambridge in the County of Cambridge, a title which became extinct upon his death. "Ernest, Lord Rutherford of Nelson."
  • In 1934 he co-discovered H3 (tritium) and He3.
  • In later life he was the President of the Royal Society of London.
  • He won 21 honourary degrees during his life.

For a longer list of achievements see Milestones in the Life and Work of Ernest Rutherford.

From NZEdge:

"... you could tell when work was going well in Rutherford’s laboratory: he strode about singing a spirited rendition of "Onward Christian Soldiers." His character, full of hearty good humour interspersed with imperious commands, was more that of a boisterous colonial farmer than the world’s leading scholar. ..."

Ernest Rutherford's other honours

Since his death Ernest Rutherford has been honoured with his portrait on New Zealand's $100 note and has appeared on several stamps around the world. See more on the Rutherford on Money & Stamps page.

Money: Stamps:

Another quote, from 1933: "The energy produced by the atom is a very poor kind of thing. Anyone who expects a source of power from the transformation of these atoms is talking moonshine."

In 1997 element 104, rutherfordium (Rf), was named after him. It is a highly radioactive synthetic (man-made) element whose most stable isotope is 265Rf with a half-life of approximately 13 hours.

Ernest Rutherford has craters named after him on the Moon and Mars.

Rutherfordine, or uranyl carbonate - UO2(CO3) - is a yellow mineral, named for Rutherford in 1906 by Dr Marckwald. Normally yellow to amber lathe like crystals up to 3mm in length. It has been reported in Tanzania, Zaire and the Northern Territory of Australia and is the only known mineral that contains only uranyl and carbonate.

For more information about Ernest Rutherford see NZ Edge's Rutherford artcle.