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440
The First idea of the atomic theory
The first idea of the atom originated around 440 B.C. and the idea was from Greek philosopher named Democritus. Democritus proposed that all atoms are small, hard particles made of a single material. He also claimed that atoms are always moving and that they form diffrent materials by joining together. -
Period: 460 to 470
About Democritus
Democritus was an Ancient Grek philosopher born in Abdera, Thance in Greece. A pupil of Leucippus, he was an influential pre-Socratic philosopher who formulated an atomic theory. -
Revision of the Atomic Theroy
British chemist John Dalton made the next major revision of the atomic theroy. His theroy had three main parts: 1. All substance are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed. 2. Atoms of the same element are exactly alike, and atoms of diffrent elements are diffrent. 3. Atoms join with other atoms to make new substances. -
Period: to
About John Dalton
John Dalton was an English chemist, meteorologist and physicist. He is best known for his pioneering worrk in the development of modern atomic theory. -
Period: to
About J.J. Thomson
Sir Joseph John "J.J." Thomson, was a British physicist. In 1897 Thomson showed that cathode rays were composed of a previously unknown negatively charged particle. -
Period: to
About Ernest Rutherford
Ernest Rutherford, 1st Baron Rutherford of Nelson was a New Zealand-born British physicist who became known as the father of nuclear physics. Encyclopedia Britannica considers him ot be the greatest experimentalist since Michael Faraday. -
Period: to
About Niels Bohr
Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory. -
New discovery in the atomic theroy
J. J. Thomson made a discovery that required a revision of the atomic theroy. Using a cathode - ray tube he discoverd that a positive plate would attract an invisible beam . He concluded that this beam must contain particles that have a negative charge. He calls these particles corpuscles but today we call them electrons. The picture represent known as the plum - pudding model. Inside it's filled with positive charge material with negative charged particles. -
Ernest Rutherford's experiment
Ernest Rutherford made an experiment and he was surpised by the results. If he aimed positively charges particles at a thin sheet of gold foil. Most of the perticles passed right through the sheet, but some were slightly deflected or even bounce back. In 1911 he revised the atomic theory. In it he proposed the idea of the nucleus. The nucleus of a gold atom was 100,000 times smaller that the diameter of the entire atom. -
Niels Bohr's discovery
Niels Bohr discovered that electrons travel around the nucleus in definite paths. These paths are located in leves at certain distances form the nucleus. He theorized that elelctrons can "jump" from a path in one level to a path in another level. -
What we know today
Through the work of many 20th century scientist, we know that electrons do not travel in definite paths as Bohr suggested. Instead they are loacted in electron clouds where they are liekly to be Bohr's model.
