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100
Democritus
(400bc)
He broke a pice of gold and saw that it is still a pice of gold but is smaller. So using methods of deduction, he came to the conclusion that all things on earth are made of atoms(from the greek word "atomos" meaning the smallest unit of matter).toms are indestructable. An empty space exists between atoms. Atoms are solid. Atoms have no internal structure. Atoms differ in size, shape, mass, position, arrangement, etc.. -
John Dalton
Dalton based his work of Antoine Lavoisier. Theorized that atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties; atoms can’t be created or destroyed; in chemical reactions, atoms are combined, separate or rearranged. From this point on, atomic theory is based off his findings.
proposed a system of symbols to represent atoms of different elements. -
William Crookes
Crookes' major contribution was the development of a better vacuum pump that allowed him to produce cathode-ray tubes with a smaller residual gas pressure. Crookes not only confirmed the previous work of scientists.. -
Henri Becuerel
Henri was experimenting with an ore containing uranium in his lab and found on accident that if he left it on a photographic plate without any light the ore still left an image like x-rays did. That happened because uranium is radioactive and that led to the discovery of natural radioactivity. -
J.J.Thomson
He discovered that all atoms have electrons outside the nucleus. He discovered this by doing a series of experiments by putting a magnet in a high-vacuum cathode-ray tube. Thomson electrically charged plates and magnets as evidence of "bodies smaller than regular atoms." This experiment helped him discover electrons and how they are in every ingle atom; today we call them electrons. By 1904 developed a picture of his atom. It looks like a muffin with berries scattered through it. -
Ernest Rutherford
By shooting small positively charged particles at a thin gold foil sheet. He discovered 99% of the particles that traveled through the gold foil missed the nucleus. He calculated the size of the nucleus to be at least 10,000 times smaller than the size of the whole atom. He also discovered: all atoms are unchangeable, elements are characterized by atomic mass, and when elements react, their atoms combine in whole number ratios. He hypothisised that electrons have sertin orbits but the exp. fail -
Neils Bohr
He applied the quantum theory to Rutherford's atomic structure by assuming that all electrons travel in stationary orbits defined by their momentum. This led to possible energy levels for their orbits. He came to the conclusion that electrons aren’t just randomly located around the nucleus, but they have certain orbits. He scetched his atomic model. -
James Cladwick
James Chadwick discovered the neutrally-charged neutron. Chadwick did a test on Beryllium and bombarded the element with alpha particles. This caused some of the protons to be discharged, creating neutrons. -
Today's Acepted Model
Today, usualy the Bohr model is used. Although the Chadwick model is ofen used as well.
