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Aristotle and Democritus
Aristotle - 0350 BC disbelieved that the theory the ancient Greek theory of atoms being different sizes and shapes. He also thought that atoms are not in constant motion in the void. Developed theory that all matter is either Fire,Water,Earth or Air. With the four qualities of dryness, coldness, hotness and moistness.
Democritus developed the conservation of energy and irreducibility of matter principles. -
Antoine Lavoiser
Developed the law of conservation of mass. States that any system closed to all transfers in energy and matter, the mass of the system must remain constant overtime. Even in a chemical reaction mass can not be created or destroyed. -
John Dalton
British chemist and physicist. Developed the atomic theory. He purposed that matter is composed up of differing weights of atoms, and that all atoms of a given element are identical. He also created the spherical model which was purposed as a dense ball of matter. -
Joseph Proust
Created the law of definite proportions, states that a chemical compound always contains exactly the same proportion of elements by mass, however the element can be altered. -
William Roentgen
Discovered x-rays when working with cathode rays. He discovered this when he found that that rays could go throught solid objects. -
J.J Thomson
In 1897 he suggested that there is a unit that is 1000x smaller then an atom. suggesting that there was subatomic particles, now known as electrons. He discovered this throught the means of cathode rays. Concluded that the cathode rays were over 1000x smaller then an hydrogen atom, but the mass was the same, bringing him to the conclusion that the rays constructed out of negitively charges particles, Created plum pudding model, electrons and unknown posistive charges were in a bubble together. -
Frederick Soddy
Discovered that the decay of radioative elements can create new elements. But also this decay produced alpha, beta and gamma radiation. This is significant because when radioactivity was discovered no one knew what the transformation was. -
Robert Millikan
Oil Drop experiment in 1909 - Conducted the Oil Drop Experiment and determined the charge of a single electron, By using J.J Thomson's charge-to-mass ration. He determined the charge of a electron as well. -
Ernest Rutherford
Was the most out-going researchers of atomic physics. In 1918 Rutherford discovered that when alpha particles were then shot at a gold foil, only some went throught while some bounced back proving that they were repelling other positively charged particles in the atom. He also developed the Nuclear model, where the nucleaus was the center point of the atom which was made up of protons. -
Neils Bohr
He purposed that electrons where orbiting around the nucleas of the atom. These electrons could up or switch when their energy levels permit it. This brought the new Nuclear model, called the Rutherford-Bohr model where the atomic model has energy levels of electrons orbiting. -
Werner Heisenberg
Came up with the Uncertainty principle. It ascribes the uncertainty in the measure of quantities to the jolt disturbance triggered by the act of observation. This is not totally valid becuase the loss of precision is less than the predicted by Heisenberg, the mathematical result remains valid however. -
James Chadwick
British physicist, he measured the energy of protons in hydrogen atoms. He then made the discovery of Neutrons, atomic particles that have no charge. -
Otto Hahn, Lise Meitner, and Fritz Strassmann
These four became the first to recognize that the Uranium atom, when shot with neutrons, can split. They found that when it split, mass was converted into energy.
