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What he hypothesized:
Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms. -
There are only four elements that the world is made up of Earth, fire, water, air. He also proposed a fifth element, aether.
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His atomic theory said that elements consisted of tiny particles called atoms. A compound is a pure (one of a kind) substance due to different elements bonded together. They are not easily separated from one another.
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J.J. Thomson discovered the Electron.
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She announced the discovery of two new elements, radium and polonium.
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Rutherford discovered that atoms have small, charged nuclei.
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Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus.
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Max Planck originated the Quantum Theory
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R. Millikan made it possible to measure the charge of an electron
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Werner Heisenberg created the Theory of Uncertainty Principle
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Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position.
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His discovery was that electrons have properties of both waves and particles
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James Chadwick discovered the Neutron
