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Lesson 7: Atoms 1: Early History

Introduction

The next three lessons are about the history of ideas about atoms.  This will help us understand alpha, beta and gamma radiation.  We’ll also learn some more about how science works.

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Philosophy means love of knowledge

Our story begins with the Ancient Greek philosophers who were at their peak for 200 years from about 500 BC.

They saw clouds and trees and mountains and animals and people and stars and fire and everything else in the world.  They wanted to know where all these things came from, what they were really made of and how they could be explained.  Explaining everything that exists (as well as love, morals, laws and government) is not a small task, as you can imagine.

The Greek philosophers didn’t want to use gods and ancient stories to explain why trees grow or why fire is hot.  They thought you could know about the world by looking carefully, thinking very hard and discussing your ideas.  Ancient Greek philosophers did not do experiments but in other ways their approach was a bit like modern science.

Atoms helped solve the problem of change

Some of the questions that they wanted to answer may seem a bit strange to us.  One question early philosophers asked was ‘can something come from nothing?’  For example, when you see a tree growing, does new ‘tree stuff’ get created from nowhere?  If it is impossible for new stuff to be created then everything in the world must have been around forever.  But how is it possible for anything to change: for clouds to form, for people to grow old?

One way round this problem is to imagine that the world is made up of invisible particles called ‘atoms’.  The Ancient Greeks imagined that these atoms had always existed and were never created or destroyed.  They were continuously moving and were surrounded by completely empty space.  When we see something change like flour being baked into bread it is the atoms changing their movement and position in space.

Democritus - the laughing philosopher

One of the founders of the idea of atoms was called Democritus.  He is sometimes called ‘the laughing philosopher’ because he valued happiness so much.  Democritus argued that there were an infinite number of different types of atoms.  They were every kind of shape and size but they were all made from the same stuff.  Democritus imagined that we couldn’t sense atoms directly.  We couldn’t see, hear, touch, smell or taste them.

A substance was solid or liquid, hot or cold, spicey or sweet because of the shape of its atoms and because of how they moved and because of how much space there was between them.  Democritus even imagined that there were atoms for the soul.

Remember that Democritus didn’t do any experiments or have a special microscope.  His atoms were an invention of his own imagination.  They helped him explain the world but they weren’t used to ‘discover’ new things.

Atom means uncuttable - so there's nothing smaller

A-tom means ‘un-cuttable’.  So atoms can’t be ‘cut’ into smaller pieces.  They are as small as you can go.  The ‘tom’ bit is also found in ‘tomography’ which means showing a picture of slices, or ‘cuts’, through something, like a tumour.

Aristotle didn't like the idea of atoms

The idea of atoms fell out of favour because the most influential Greek philosopher, Aristotle, did not agree with them.  He held the ancient view that everything on Earth is made of four elements: earth, air, fire and water.

The sun, moon and stars moved in unchanging perfect circles and were made of a divine substance not found on Earth called ‘aether’.

So Democritus saw the world as being made of one only type of stuff, divided into lots of different shaped atoms, in empty space.  Aristotle saw the universe being made of five different elements, which didn’t come as atoms and empty space was impossible.

The ancient Greek philosophers were intellectual superstars

We may look at Ancient Greek philosophers like Aristotle with their strange clothes and odd ideas and think of them as rather silly children.  But they were geniuses.  Their theories were incredibly rich and sophisticated.  Far more so than we have time to show here.  If they lived now they would be world leaders, internet billionaires and Nobel prize winners.

Ancient Greek ideas about the world were almost all wrong.  But their ideas about how to weigh up different arguments, called ‘logic’, is still used today.  It is their approach which was so important: looking at the world, thinking hard and openly debating their different theories.

Aristotle's ideas held sway for about 2000 years

But it was Aristotle’s five elements that were a core theory for the best part of 2000 years, well into the seventeenth century.

Remember that Aristotle’s theories said the heavens were made of special stuff called ‘aether’ and that everything had a purpose.  This suited the Roman Catholic church because it made heaven special and allowed God to decide what the purpose of things was.

The problem was that it wasn’t a very good core theory because it didn’t really suggest new areas to study or predict new things to find.  There was lots of activity trying to turn ordinary metals into gold and find a cure for all illnesses but very little in the way of success.

The Enlightenment

During the late seventeenth and eighteenth centuries there was an explosion of ideas in Europe called the ‘Enlightenment’.

Scientists wanted to break away from the stale old ideas of Aristotle and build better scientific theories from scratch.  Many scientists began using the idea of atoms but there weren’t any really good experiments to convince everyone that they existed.

Antoine Lavoisier makes very precise measurements

One problem was that scientists didn’t have any way of making very precise measurements.

The French scientist Antoine Lavoisier designed a very sensitive weighing balance.  He used it to show that during a chemical reaction, for example burning some wood, there was no loss of mass.  Lavoisier seemed to have helped answer the Greeks’ question ‘can something come from nothing?’.  No.  The amount of stuff is constant.

John Dalton uses atoms to explain chemistry

If stuff was made from atoms then it looked like atoms were never destroyed.  But was stuff really made from atoms?

Another related question was: How many different types of basic stuff or ‘elements’ are there?  For thousands of years humans had known how to separate out gold, silver, copper, lead and a few other elements.

In the 1700s nineteen new elements were discovered: four times as many as in the previous 500 years.  How did the idea of all of these newly discovered chemical elements fit in with the idea of atoms?  No one was really sure.

Scientists started making very precise measurements of mass in chemical reactions.  They also measured volumes of gases.  They found that two elements reacted in the same ratio by mass.  For example 1g reacted with 3g, 2g with 6g, 3g with 9g, etc.

The Englishman, John Dalton used these experimental results to propose a universal atomic theory.

This said that what makes an element is that it is made of only one type of atom.Oxygen is made from only oxygen atoms, hydrogen from only hydrogen atoms and so on.  The atoms of one element are different from any other.  Oxygen atoms are different from hydrogen atoms and sulphur atoms.  Atoms never change from one element to another.

Chemical reaction don’t make or destroy atoms they just change the way atoms are grouped together.  So when hydrogen and oxygen react together they form water.  Water is just combined hydrogen and oxygen atoms.  Dalton had no idea why or how atoms combined in chemical reactions.  He speculated they might have little hooks.

There was a lot of work still to do before Dalton’s theory became a really stable core.  So at the end of this lesson we have found that an element is defined as a substance whose atoms are all the same.

Dalton knew that the atoms of different elements had different masses.  But was an atom as small as you could go?  Were atoms themselves made up of smaller parts?

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