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Dalton
Dalton, a British chemist, wanted to know why elements combine in certain proportions based on mass to form compounds. He expirmented with different substances. His results suggested that elements combine in certain proportions because they are made of single atoms. -
Thompson
J.J. Thomosn, a British scientist, showed that there was a mistake in Dalton's theory. Thompson discovered that there were small particals inside of the atom. This means that atoms can be divided into even smaller parts. -
Rutherford
Ernest Rutherford, a former student of Thompson's, decided to test Thompson's theory. He designed an expirment to study the parts of an atom. He aimed a beam of small, positively charged particals at a thin sheet of gold foil. He ut a special coating behind the foil. The coating glowed when hit bu the positively charged particlas. He could then see where the particals went after hitting the gold. -
Rutherford
Rutherford revised the atomic theory. He made a new model of the atom. Rutherford proposed that in the center of the atom is a tiny, extremely dense, positively charged part called the nucleus. He calculated that the diameter of the nucleus was 100,000 times smaller than the diameter of the gold atom. -
Bohr
Niels Bohr, a Danish scientist who worked with Rutherford, studied the way that atoms react with light. Bohr's results led him to propose that electrons move around the nucleus in certin paths, or energy levels. In Bohr's model, there are no paths between the levels. But electrons can jump from a path in one level to a path in another level. Bhor's model was a valuable tool in predicting some atomic behavior, but the thomic theory still had room for improvement... -
440 BCE - Democritus
Democritus was a greek philosopher that founded atoms. The word atom is form the greek word atomos, meaning "not able to be divided." Democritus said that atoms are small, hard particals. He thought that atoms were made of single material formed into different shapes and sizes. -
Schrodinger & Heisenberg - 20th Century
Schrodinger & Heisenberg did impostant work on our current understanding of the atom. The exact path of an electron cannot be predicted. According to the current theory, there are regions inside the atom where electrons are likely to be found. Tehy are called electron clouds. -
Aristotle - 440 BC
Aristotle believed that you could never end up with a partical that could not be cut. He had such a strong influence on peoples ideas that for a long time, most people thought he was right. -
Period: to
The Development of Atomic Theory
