The Enigmatic Electron: Electron Behaviour and How It Influences Our Lives

By Ann Jones

The electron, discovered in 1897, was found to be a constituent of all atoms. While the nucleus of the atom remains fixed, the electrons are free to move with different amounts of energy. When supplied with more energy, by physical or mechanical means, light is produced when the original energy state is reached. Electrons can easily be removed altogether from the atom as in the case of electric current. This has given rise to our electrical and electronic industries. The associated magnetic field allowed motors and dynamos to be developed. Rapid movement of electrons results in the production of electromagnetic waves, from the longest wavelengths (radio waves) to the shortest wavelengths (gamma rays). This has had a huge impact on our lives in the fields of medicine and telecommunications. A beam of electrons can be directed in the same way as a beam of light. As light can show wave/particle duality so can an electron beam. Its measured wavelength is about the same as X-rays. This means electrons can be diffracted. The famous ‘double-slit’ experiment where a single electron appears to ‘interfere with itself’ cannot be explained by classical physics and so we enter the strange world of quantum mechanics. The birth of the quantum computer is not far away and will be much faster than existing computers. Finally, all chemical reactions are the result of electron movement between reactants.

• Language: English
• Publisher: Austin Macauley Publishers
• Release date: Jul 30, 2021
• ISBN: 9781528996273

Ann Jones

Ann Jones is married with two children and lives in the market town of Ashby-de-la-Zouch. She has a degree in combined science, physics and chemistry, from The University of Manchester. She has worked as a research scientist with metals and materials and became a teacher during the latter part of her career, concentrating on all three sciences up to GCSE level. She has maintained a keen interest in science and likes to keep abreast of modern developments.

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About the Author

Ann Jones is married with two children and lives in the market town of Ashby-de-la-Zouch. She has a degree in combined science, physics and chemistry, from The University of Manchester. She has worked as a research scientist with metals and materials and became a teacher during the latter part of her career, concentrating on all three sciences up to GCSE level. She has maintained a keen interest in science and likes to keep abreast of modern developments.

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Ann Jones (2021)

The right of Ann Jones to be identified as author of this work has been asserted by the author in accordance with section 77 and 78 of the Copyright, Designs and Patents Act 1988.

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A CIP catalogue record for this title is available from the British Library.

ISBN 9781528996259 (Paperback)

ISBN 9781528996266 (Hardback)

ISBN 9781528996273 (ePub e-book)

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Acknowledgement

My thanks go to my family for all their help and support.

Introduction

The 4th of July 2012 was a defining moment in the field of Particle Physics. Two huge particle detectors, the ATLAS and the CMS, situated in the ring of the Large Hadron Collider, provided evidence for the existence of the Higgs boson. This is the particle which gives all other elementary particles mass, and is the final missing piece in the Standard Model of Particle Physics. The Standard Model is a quantum theory that explains three of the four fundamental forces—electromagnetism (the force of attraction between positive and negative particles e.g. a proton and an electron), the strong force (which binds protons and neutrons together in the nuclei of atoms) and the weak force (which is responsible for radioactive decay in certain unstable nuclei). To date, a force field giving particles mass had not been discovered. Theory suggested that the particle responsible, i.e. the Higgs boson, would require a huge amount of energy to detect, which had not been available until the development of the Large Hadron Collider.

There was tremendous excitement on that July morning when the results from the two detectors were announced (and further data has shown that the Higgs particle exists). Hopefully, the discovery will shed light on the nature of so-called ‘dark matter’⁹ which is thought to fill most of the Universe and also what the Universe may have looked like in its early stages when gravity combined with the other three forces.

Could there have been the same amount of excitement when J. J. Thomson¹ (1856–1940) discovered the electron? At the time, no one could have foreseen the importance of this tiny negatively charged particle (about a 1000 times lighter than a hydrogen ion or proton).

It was thought that the electron was formed one second after the Big Bang 13.8 million years ago, along with protons, neutrons and other particles. Electrons are normally bound up inside atoms, where their total negative charge is balanced by the positive charge of the protons in the nucleus, thereby rendering the atom neutral. They are distributed in ‘shells’ around the nucleus of the atom and held in position by the force of attraction from the positive nucleus. Electrons are responsible for the way in which atoms behave in chemical reactions. However, electrons can be removed from atoms by force, for example, friction or an electric field, which is exactly what Thomson did.

J. J. Thomson studied Physics at Owens College, Manchester and, from there, became a mathematical physicist at Trinity College, Cambridge. In 1884, he was elevated to the post of Cavendish Professorship of Experimental Physics where he demonstrated his flair for designing apparatus and problem-solving.

This book endeavours to explain how electron behaviour was understood and how it has transformed our lives. It is non-mathematical and is designed for those who have a basic scientific knowledge but would like to discover more.

Chapter 1

Discovery

Around 1869–1875, Sir William Crookes¹ (1832–1919) was experimenting with discharge tubes. These are cylindrical glass tubes, fitted with a pair of electrodes (an anode and a cathode) and filled with a gas at low pressure.

1

Fig. 1: A gas discharge tube

Discharge tubes had been found, in the early part of the 20th century, to glow with different bright colours depending on the type of gas within, when a high voltage was applied between anode and cathode. If the pressure of the gas inside the discharge tube is sufficiently low, electrons emanating from the cathode collide with the gas molecules causing them to ‘ionise’. This means that electrons are knocked out of the gas molecules, leaving positively charged particles called ions. These ions are accelerated towards the negative cathode where they knock out further electrons from the gas molecules. Collisions between ions, electrons and gas atoms inside the tube cause some atoms to be excited i.e. their electrons gain sufficient energy to reach a higher energy level. When they fall back to their original energy level, the extra energy is emitted as light. The colour is characteristic of the element inside the tube.

Discharge tubes are used extensively today in advertising displays; neon gas glows bright red while oxygen and nitrogen give a purple glow.

The gas inside must be at sufficiently low pressure, otherwise too many atoms or molecules ‘get in the way’ and prevent ionisation. Crookes showed that the gases were conducting electricity. By 1870, he was able to create a high vacuum inside the discharge tube by extracting most of the gas, using a vacuum pump.

However, he had noticed that there was a dark space just beyond the cathode which was later known as Crookes or, sometimes, Faraday’s dark space, after the eminent physicist Michael Faraday¹ (1791–­­1867), famous for his work on electromagnetism. When a high voltage was applied, the dark space occupied most of the tube except for a glow at the far end. What was going on? A relatively low number of gas molecules in the tube means that the cathode rays which have been accelerated