B. H. Fields - Understanding Electrons

To Elon, for the electricity he brings to life.

Published in 2016 by Cavendish Square Publishing, LLC
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Copyright 2016 by Cavendish Square Publishing, LLC

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Library of Congress Cataloging-in-Publication Data

Bortz, Fred.
Understanding electrons / by Fred Bortz and B.H. Fields.
p. cm. (Exploring the subatomic world)

Includes index.

ISBN 978-1-50260-538-2 (hardcover) ISBN 978-1-50260-539-9 (ebook)

1. Electrons Juvenile literature. I. Bortz, Fred, 1944-. II. Title.

QC793.5.E62 B67 2016

539.72112d23

Editorial Director: David McNamara

Editor: Andrew Coddington

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Printed in the United States of America

Contents

Discovering the Electron

Electricity and Magnetism, Matter and Light

How Electrons Explain Chemistry

Electronic Technology

W hat would modern life be like without electronics? We live surrounded by devices. We connect to each other through computers and the Internet. We use pocket-sized cellular phones to communicate by voice, text, pictures, or video. We watch and listen to news, opinions, music, and entertainment on radio, television, and streaming audio and video. We can cook with microwaves instead of gas or electricity. We have global positioning system (GPS) receivers small enough to hold in one hand or mount on car windshields. Their programs and detailed maps tell us where we are in the world and how to get to our destination. Robots with electronic controls work in factories, hospitals, and even on other planets.

All of that technology has grown from our understanding of electrons, which are among the lightest bits of matter known to science. We can trace that very modern understanding back to a very ancient question. About 2,500 years ago, Greek philosopher Democritus and his mentor, Leucippus, asked, What is matter made of?

Democritus and Leucippus imagined cutting a piece of matter in half, then cutting one of its halves in half, then cutting one of those pieces in half, and so on until the resulting pieces could no longer be cut. The last pieces would be indivisible, or atomos in Greek. Democrituss atoms turned out to be similar to what we call molecules today. A water moleculetwo hydrogen atoms combined with one oxygen atomis not indivisible, but it is the smallest speck of matter that can still be called water.

Hydrogen and oxygen are examples of substances that scientists call elements. In a pure element, all the atoms are the same. Scientists classify water as a compound, a substance with more than one kind of atom, but with all its atoms combined into the same kind of molecules. The science of chemistry deals with the way atoms and molecules interact, react, and combine.

If molecules can be divided into atoms, it is natural to ask if atoms can also be divided. And if so, might we look into the atom to understand why only certain combinations of atoms form molecules. A little more than a century ago, physicists began to answer those questions. As they probed inside atoms, they found a deeper understanding of not only the chemical behavior of matter, but also other phenomena such as electricity, magnetism, and light.

This book contains the story of the first subatomic particle to be discovered (the electron) and explores the knowledge and technological advances that people have gained from studying it.

DISCOVERING
the Electron

O ur story begins at the world-famous Cavendish Laboratory at Britains Cambridge University. A twenty-four-year-old scientist named Joseph John J. J. Thomson (18561940) arrived there in 1881, and he found that the atmosphere there was electric in more ways than one. The laboratorys founder, James Clerk Maxwell (18311879), was famous for formulating a set of four equations that described the relationship between electricity, magnetism, and light waves. Thomson hoped to follow in his footsteps.

Other major discoveries of that time came from chemistry. By studying the reactions between different substances, chemists had concluded that matter was composed of atoms, and that atoms combined in particular ways to form molecules. They thought those atoms were indivisible. They also had discovered that electricity was related to chemical reactions. But where the electrical nature of matter came from remained a mystery.

Cathode Ray Experiments

Young Thomson wanted to use his mathematical gifts to make discoveries about the electrical nature of matter just as Maxwell had done for the electromagnetic nature of light. But his boss, John William Strutt (18421919), more commonly called Lord Rayleigh, who became Cavendish Professor in 1879 after Maxwells death, had other plans. Rayleigh believed that in physics, mathematical skills should not stand alone. If Thomson intended to work at the Cavendish, he would have to do more than calculation. He would have to work in the laboratory!

Unfortunately, Thomson was not very skilled with scientific apparatus. His contributions to experiments were more of the mind than of the hand. J. J. was very awkward with his fingers, and I found it very necessary not to encourage him to handle the instruments! said H. F. Newall (18571944), Thomsons assistant in his early years at the lab. But he was very helpful in talking over the ways in which he thought things ought to go.