The Atomic Theory: How it all started

2500 years ago, Greek philosophers didn’t know if matter kept being split into smaller and smaller parts or if there was ever going to be a smallest piece. These philosopher decided that the smallest piece of matter was going to be called atamos. But a very respected philosopher by the name of Aristotle said that all matter is made of tiny particles called atoms. Everyone respected Aristotle so much, that no one changed his opinion for 2000 years.

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In the 18^th and 19^th Century, there were researchers named Alchemists that worked in Europe to see if matter such as lead and mercury could be turned into gold. Their idea was more technologic than scientific. Their results were that nothing turned into gold.

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John Dalton was born in 1766 and died in 1844. He was a British schoolteacher and a scholar. He was interested in the gases that make up the earth so he investigated the composition of many substances such as carbon dioxide, water and nitrogen oxide. Dalton explained that the particles or matter are made up of tiny hard spheres that are different for every element. He said that the atom was the smallest part of an element.

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J. J. Thomson was born in 1856 and died in 1940. He said that in 1897, the currents were streams of negatively charged particles which were later called electrons. He found out that all substances used in discharge tubes made these particles. Thomson then hypothesized that if his experiment showed that there were small particles, every element must have these. He made a model csalled the ‘raisin bun’ which showed that atoms have smaller particles called electrons. But he was soonly proved by his student Erenest Rutherford that he had a more accurate picture of the atom.

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Erenest Rutherford was born in 1871 and died in 1937. He was a scientist from New Zealand who worked at McGill University in Montral. He made an experiment which consisted of a thin sheet of gold, a fluorescent screen and some alpha particles. He placed the sheet of gold inside the fluorescent screen with one opening so that the alpha particles could zoom through the opeing and bounce, deflect and reflect through the sheet of gold. When he did this, he was able to see the alpha particles. His results showed that most of the atoms went through the gold without being affected. He suspected this because he knew there were spaces between particles. He also found out about the nucleus – the charged center of an atom. This was an important discovery and he found out that there are at least 2 types of particles in one atom. One is a proton, which has a positive electric charge, and the other is a neutron, which has no electric charge.

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Nuels Bohr lived frim 1885 to 1962. He was a Danish physicist working under Rutherford. His theory was that electrons surrounded the nucleus in a specific energy ‘level’ or ‘shell’. This meant that each electron had a particular amount of energy.