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200
Democritus 440 BC
He was a Greek philospher and the first person to realize that an atom could not be divided into smaller particles. -
200
Aristotle 382 B.C
Aristotle is a Greek philosopher and he disagreed with Democritus's ideas. He believed that you would never end up with a particle that could not be cut. Most people thought he was right because he had such a strong influence on people's ideas for such a long time. Democritus was right though. Matter is the smallest particle into which an element can be divided and still be the same substance. -
John Dalton
He published the Atomic Theory in 1803. It said all substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed, and two other rules. -
J.J Thomson
He is a british scientist that discovered that there are small particles inside the atom. He now discovered particles called electrons. -
Period: to
The devolement of Atomic Theory
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Ernest Rutherford 1909
Rutherford designed an experiment to study the parts of atoms. He aimed a beam of small, positively charged particles at a thin sheet of gold foil. Rutherford put a special coating behind the foil, it glowed when hit by the positively charged particles. Rutherford could then see where the particles went after hitting the gold. -
Rutherford 1911
Rutherford revised the atomic theory. He made a new model of the atom. He proposed that in the center of the atom is a tiny, extremely dense, positively charged part called the nucleus. Rutherford calculated that the diameter of the nucleus was 100,000 times smaller than the diameter of the gold atom. -
Niels Bohr
Niels is a Danish scientist who worked with Rutherford, studied the way that atoms react to light. Bohr's results led him to propose that electrons move around the nucleus in certain paths, or energy levels. But electrons can jump from a path in one level to a path in another level. Bohr's model was a valuable tool in predicting some atomic behavior, but the atomic theory still had room for improvement. -
Erwin Schrodinger and Werner Heisenberg
Erwin and Werner did especially important work. They further explained the nature of electrons in the atom. They figured out there were regions where electrons move which is called the electron cloud.
