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350 B.C -Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air.
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at the beginnig Democritus thought matter could not be divided indefinitely, which maked the idea of atoms in a void.
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its ideas were :
•All matter is made of atoms.
•Atoms of an element are identical.
•Each element has different atoms.
•Atoms of different elements combine in constant ratios to form compounds.
•Atoms are rearranged in reactions. -
Thomson discovered that electrons had a negative charge and thought that matter must have a positive charge.
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Max Planck,showed that when you vibrate atoms strong enough, such as when you heat an object until it glows, you can measure the energy only in discrete units. He called these energy packets, quanta
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Albert Einstein wrote a ground-breaking paper that explained that light absorption can release electrons from atoms, a phenomenon called the "photoelectric effect." , explaining the quanta behaved like discrete particles, called : photon
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its main idea was to explain how electrons can have stable orbits around the nucleus and showed why atoms characteristic emission spectra .
also and important idea was thtat Electrons can be bumped up to a higher shell if hit by an electron or a photon of light. -
h was the first atomic model that considered the atom consists of two parts: the "bark", consisting of all their electrons, turning at high speed around a "core" very small, which concentrates all the positive electrical charge and most of the mass of the atom.
