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300
Aristotle
(300 BC) Aristotle's atomic theory was based off of water, fire, earth and air. He didn't believe in atoms because he thought they were ultimately "small". He also believed there were 4 qualities of to these elements, which were hotness, dryness, coldness and moistness. He disagreed with Democritus' theory very much so. -
400
Democritus
(400 BC) His atomic theory revolves around the fact that atoms are present in the atmosphere. Atoms do not have a specific size and can differ. Also, all atoms are present in solids and liquid and are unable to be seperated. -
Antoine Lavoisier
Antoine discovered oxygen and hydrogen. He also came up with and also created the Law of Conservation of Mass. This law concludes that during a chemical reaction, mass or matter is neither created or destroyed. It is only changed. -
Joseph Louis Proust
Joseph defined the Law of Definite Proportion. This law states that when different elements combine to form a pure compound, the ratio will stay the same. -
John Dalton
John Dalton came with his Atomic Theory. He discovered that certain gases only could be combined in certain proportions even if two different compounds shared the same group of elements or common element. -
Michael Faraday
Michael was mainly known for studying electricity, but he also studied gases such as chlorine. He would diffuse them. He also studied the idea of elements forming into compounds. On January 3rd, 1832 he studied the effects of electricity on atoms and named the phrase "electrolysis". -
Henri Becquerel
He was studying phosphorescence of uranium salts, he noticed that the photographic plates had already been exposed despite not being exposed to bright sunlight. He realized it was due to natural radioactivity which was then referred to a 'spontaneous radioactivity". -
Marie and Pierre Curie
The couple are known for discovering the two elements radium and polonium when they were were investigating radioactive substances. In 1903, Marie was awarded with the Noble Prize for physics; along with Henri Becquerel. -
Max Planck
He discovered that electromagnetic energy is released in quatized specific amounts. In the formula to find the amount of energy that is released when electrons jump energy levels, he is plankcs constant. He is considered to be the founder of the quantum theory. -
J.J. Thomson
J.J. conducted the Plum Pudding Model! In 1897, he discovered the electron by using the cathode ray tube. It wasn't until 1904 that he came up with a theory with coincided with the structure of the atom. He noted that the structure consisted of negatively charged electrons "floating" in a positively charged cloud. He called this the Plum Puddin g Model because it looked like plums floating in pudding. -
Albert Einstein
Einstein developed the special and general theories of relativity. His results helped scientists learn where the electron clouds might be. In 1921 he recieved the Nobel Prize for his explanation of the photoelectric effect. -
Ernest Rutherford
Ernest conducted the gold foil experiment to study the atom. He hypothesized that the + particles that he shot would all pass through the foil. However, some came straight back. This experiment proved that the nucleus was positively charged and very small, which resulted in the atom being composed of mostly empty space. -
Robert Millikan
Robert conducted an Oil Drop Experiment to determine the charge of an electron. He also used x-rays to help find the charge. In the end, he realized that electrons have relatively no charge. He determined this because he realized that the mass of an electron is only 1/1840 the mass of a proton! -
Neils Bohr
He discovered that the more energy the electron was composed of, would result in the electron being farther away from the nucleus. He also proposed the idea that you could only move from the fixed orbits of certain energy. -
James Chadwick
James discovered a new subatomic particle by observing them when Beryllium was hit with alpha particles. It emitted a strange light and the substance that was emitting the light had no charge. He came to realize that this new subatomic particle is known as the neutron. They have no charge and their function is to stabilize the nucleus of an atom by allowing protons to be close to one another.
