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440 BCE
Democritus
Beleived that if you continually cut a substance in half, eventually you would get an "uncuttable" piece. He called these uncuttable pieces particles, which means indivisible in greek.
He thought atoms were hard and small particles compiled by one substance and in one particular shape. He thought they were always moving and that they combined with each other. -
John Dalton
He claimed the reason elements combined was because all elements are made up of atoms. He also published a three- part atomic theory. 1. All particles are made of atoms, they cant be divided or destroyed. 2.Atoms of the same elements are identical diferent element's atoms are different. 3. atoms join with other substances to create new and different substances. -
Ernest Rutherford
In his gold foil experiment, Rutherford shot a positively charged beam of particles through a sheet of gold foil. He thought if the particles were soft as JJ Thomson's plum pudding model had suggested, then they would pass through and continue in a straight line, which most did. However some did not. This showed that the plum pudding model was somewhat false, so Rutherford created a new model. -
Robert Millikan
Millikan used a tiny, sub-millimeter drop of oil suspended between capacitor plates to measure the incremental charge on an electron. His reasoned that the oil drop would pick up a charge due to friction as it entered the region between the plates.The interaction of the drop with the electric field always occurred in discrete units, indicating that the electron charge was a single value, and that it was the same value for all different forms of electricity. -
Neils Bohr
This man suggested that electrons travel around the nucleus in definite paths. These paths are always at a certain "level" away from the nucleus. He also stated that electrons cannot travel in between each path, however they can jump from one path to another. -
Werner Heisenberg
Created a formulation of quantum mechanics called matrix mechanics. Matrix mechanics was the first conceptually autonomous and logically consistent formulation of quantum mechanics. He also created the Heisenberg Uncertainty Principle. The principle states that we can know the position or the momentum of a particle accurately, but not both simultaneously. -
Erwin Schrödinger
Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. The quantum mechanical model predicts the odds of the location of the electron. This model can be portrayed as a nucleus surrounded by an electron cloud. In the cloud, you are more likely to find an electron where the cloud is most dense and less likely where the cloud is the least dense. -
James Chadwick
When Herbert Becker and Walter Bothe directed alpha particles (helium nuclei) at beryllium in 1930, a strong, penetrating radiation was emitted. One hypothesis was that this could be high-energy electromagnetic radiation. In 1932, however, James Chadwick proved that it consisted of a neutral particle with about the same mass as a proton. Ernest Rutherford had earlier proposed that such a particle might exist in atomic nuclei. Its existence now proven, it was called a "neutron". -
JJ Thomson
Thomson used a cathode ray tube to infer that there are small particles inside of every atom. This inference proved Dalton's theory to be wrong. Particles can be divided. Through this experiment, Thomson also inferred that atoms must be negatively charged.Thomson proposed the plum pudding model which allowed scientific advances to occur.
