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340
Aristotle BCE
- Did not believe the atomic theory
- He thought all materials on Earth were made up of the four elements: Earth, fire, water, and air.
- Most people followed his idea causing Democritus' idea to be looked over for about 2,000 years.
- Thought Democritus' idea was worthles but used it to come up with his own ideas.
- Thought the atoms were different sizes, regular geometric shapes.
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340
Aristotle Websites
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Dalton AD
-Theory was based on the premise that the atoms of different elemnts could be distingusied by differences in their weight
- All matter is composed of atoms
-Atoms cannot be made or destoryed
-All atoms of the same element are identical
-Different elements have different types of atoms
-Chemical reactions occur when atoms are rearranged
-Compounds are formed from atoms of the constituent elements
-Atoms are the relative size and weights
www.rsc.org -
Dalton Websites
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Thomson AD
-He discovered the electron in a series of experiements designed to study the nature of electric discharge.
-he used a high vacuum cathode-ray tube to help make his discovery.
-1904 Thomson suggested a model of the atom as a sphere of positive matter. -
Thomson Websites
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Rutherford AD
-He discovered the atomic nucleus
-He discovered te disintegration of the elements and the chemistry of radio active substances
-Atoms are not always stable
-Atoms have the majority of their mass concentrated in a nucleus
-Discovered the worlds first alchemy (converting nitrogen into oxygen)
-He did the gold foil experiement
-the atom is 99% empty space
-The nucleus contains a poitive charge and most of the mass of the atom
-Nucleus is approx. 100,000 times smaller than the atom -
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Bohr AD
-The electron in a hydrogen atom travels around the nucleus in a circular orbit
-The energy of the electron in an orbit is proportional to its distance from the nucleus. The further the electron is from the nucleus, the more energy it has.
-The orbits are quantized
-Light is absorbed when an electron jumps to a higher energy orbit and emitted when an electron falls into a lower energy orbit.
-Bohr used the liquid droplet theory and the quantum theory.
-Thought the atoms looked like shells -
Bohr Websites
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Heisenberg and Schrodinger Websites
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Heisenberg and Schrodinger
-formed a model of a complete atom as interacting waves
-The particles became like vibrations on a violin string, only they were closed in circles
-His partial differential equation seemed to bear a similar relation to the mechanics of the atom as Newton's equations of motion bear to planetary astronomy.
-Werner Heisenberg formulated his uncertainty principle which says that you cannot know by measurement the position and momentum of a particle simultaneously.
- used Quantum Mechanics. -
Democritus Websites