What is an atom Building blocks All the objects you can see and feel around you your chair this book your clothes and even you yourself are made of billions of tiny atoms Atoms are the building blocks of matter They are what stuff all stuff is made of As you know there are different types of matter from wood to water paper to plastic stone to steel All these things are made of different types of atoms either on their own or in combination with other atoms All the objects and people you see around you are made up of billions and billions of tiny atoms The atoms join together in different patterns to make molecules which make up millions of substances What is matter Matter is all the materials and objects and substances around us including solids liquids and gases Not everything is matter for example light and sound are forms of energy However as scientists have discovered matter and energy are closely related and one can be turned into the other There are more than 100 types of atoms which make basic substances known as elements For example gold oxygen and iron are elements each made of just one type of atom But combined with each other the basic atoms make the millions of different substances and materials we see all around us 6
Atoms and molecules 1 H H Hydrogen molecules H H O O Oxygen molecule 2 H H H H Hydrogen atoms O O Oxygen atoms 3 H O H H O H Water molecules How small Atoms are really really tiny You cannot see individual atoms with the naked eye They are so small that 100 million atoms all lined up in a row would only reach across your little fingernail Splitting the atom It took many years to discover and understand atoms At first people believed that atoms were the smallest unit of all and that something so tiny could not be split into smaller parts But during the 20th century scientists learned otherwise They found that they could split atoms apart And what they discovered led to some hugely powerful and dangerous results In this book you'll find out how the atom was split and what it meant for all our lives Oxygen and hydrogen atoms join together in pairs to make molecules of pure oxygen and hydrogen 1 They can also split apart 2 and join with other atoms One oxygen atom joined to two hydrogen atoms makes a water molecule 3 THAT’S A FACT When you look at or touch any object you’re seeing or feeling billions of atoms packed together For example a page in this book is about one million atoms thick and one glass of fruit juice contains about 25 trillion trillion 25,000,000,000,000,000,000,000,000 atoms 7
Nothing exists except atoms and empty space everything else is just opinion Democritus declares his view of reality However that long ago there was no way of really looking at atoms and Leucippus and Democritus had no good evidence for their idea They simply thought it seemed like a sensible explanation It happened to be along the right lines according to what we know today but this was only proved in the last 200 years Ancient ideas The ancient atomists The idea that everything is made up of tiny units has been around since ancient times The name atom comes from an ancient Greek word atomos which means uncuttable or indivisible The word was first used by two ancient Greeks Leucippus and his follower Democritus who lived around 2,400 years ago They used it to describe little invisible units that they believed everything was made of They also correctly thought that there were different kinds of atoms of varying sizes which made up every kind of material People who agreed with this theory were known as the atomists Ancient Indian Buddhist thinkers around a thousand years later had similar ideas known as Buddhist atomism Democritus is such an important figure in Greek history that he was featured on the 100 drachma bank note The drachma currency was replaced by Euros in Greece in 2002 8
According to ancient Greek religion the sun was a god Helios riding his chariot across the sky But Democritus realized the sun was a phenomenon like all the other stars in the sky THAT’S A FACT Atoms weren’t the only thing that Democritus was uncannily right about He studied many subjects and came up with all sorts of ideas He claimed that the earth was round that the Milky Way was made up of stars and that early people didn’t have language but developed it gradually Scientists today have found evidence that proves all these things to be true Greek philosophers Many ancient Greek philosophers spent a lot of time wondering about how the world worked While some suggested everything was made up of atoms others thought everything was essentially made of water or from different types of air While they didn’t always guess correctly this way of asking questions and coming up with ideas was very important It paved the way for modern scientific thought and methods Breakthrough More than 2,000 years ago the ancient Greek atomists Leucippus and Democritus came up with the first theory of atoms and how they make up all substances Their ideas were not widely adopted but they would be revived much later 9
