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He was in 400 B.C.
Democritus’s was the first to come up with the idea of atoms. He stated that atoms are indestructible and that they make up everything around us. -
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Proposed the theory of conservation of matter. Proved this with the experiment of turning HGO into HG + O.
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Dalton’s theory came in four parts:
1)All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms. -
Rearranged the elements so that they were in similar groups.
The properties of elements were decided by their atomic weights. This is now called periodic law -
Kanalstrahlen is the term he came up with to describe positive ions. Studied canal rays that had opposite electrical and magnetic properties compared to an electron.
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Plum Pudding model. Solved that all atoms have a charge. This charge is now known as the electrons in an atom
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Used an oil drop experiment to prove that there are electrons with a negative charge within an atom. Did not give new model for atom, but did give prove that it gave off a charge. His accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons, which demonstrating the atomic structure of electricity.
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Showed that an atom had a nucleus. He also showed that the nucleus was very dense, very small and positively charged. He assumed that the electrons were located outside the nucleus after his experimenting.
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Determined the charge of the nuclei of most atoms. This helped arrange the periodic table based on number instead of weight.
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He came up with the idea that energy emitted by a resonator could only be in quanta.
He also figured out a new set of units for mass and length. -
The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.
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Proposed Principle of Indeterminacy - you can not know both the position and velocity of a particle.
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Combined the equations for the behavior of waves with the de Broglie equation to get a mathematical model for the distribution of electrons in an atom.
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James predicted the atom would have a neutron. He established that atomic number is determined by the numbers of protons in an atom. He also discovered the fourth subatomic particle,the neutron.
