One of the main quests of science throughout the ages has been to discover what matter is made of - and what holds it together.
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All matter is made out of many tiny particles called atoms. The study of how these atoms interact is called chemistry. Modern physics has discovered how atoms are made up of smaller particles and how these particles interact to build atoms into molecules and larger objects of matter.
The philosopher Democritus came very close to our modern understanding when he proposed that everything is made up of very small particles, which he called atoms, from the Greek atomus, for 'indivisible'.
In the 1600s, Sir Isaac Newton and other scientists experimented with materials, light, and heat, and developed many basic laws of physics. By the early 1800s, the theory of the atom became popular. By the 1900s, scientists had discovered that atoms are themselves made of even smaller particles. This century research in particle physics has taken us deep into the heart of the atom, far beyond the limits of the most powerful conventional microscopes.
The Building Blocks of Matter
What is matter made of? If you could see the smallest piece of matter, what would it look like? If you cut a piece of material into halves, and cut one of the halves into halves, and then continued cutting halves into halves - assuming you had a very fine blade and a very powerful microscope - could you continue cutting forever?
Until very recently, there was no microscope powerful enough to see the 'building blocks' of matter. But scientists were able to deduce that there were fundamental particles, which they called atoms (for indivisible), by performing experiments such as firing electrons into targets and seeing how the pieces came out.
Atoms are extremely small particles, out of which all matter is made. They are the smallest particles of a chemical element that still have the properties of that element.
A typical atom is about one millionth of a millimetre across - a million of them laid in a line would measure one millimetre across. The lightest atom is that of hydrogen, while one of the heaviest is that of uranium - about 200 times heavier than hydrogen.
Splitting large atoms into smaller ones or 'fusing' small ones to create larger ones, releases energy - this is what happens inside nuclear reactors and atom bombs (fission) and inside hydrogen bombs and the sun (fusion).