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Democritus- In the year 400 B.C. he discovered the atom itself and what its job was. He was the philosopher who founded the original atomic theory so without his discovery, we would have no modern atomic theory.
One of his experiments in which he truly discovered the atom, was when he broke a seashell in half over and over again. Then finally, he was left with a fine powder and then found the smallest piece and tried to break it but couldn’t. He discovered that atoms were the building block to all matter. -
John Dalton-He was the man who created the first useful atomic theory in 1803.
He had done observations while he was in the course of his studies in meteorology. During his observations, he concluded that water evaporated into the sky and existed in the air as an independent gas, due to the air particles mixing in with air particles. Then, he later began to experiment with other mixtures of gases to determine what effect properties of the individual gases had on the whole mixture. -
J.J. Thomson Experiment
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J.J. Thomson-He conducted an experiment in 1897 in which created controversy between physicists around the world and German scientists involving cathode rays and in 1904 created the plum-pudding model.
Thomson’s experiment showed that cathode rays were particles with negative charge and much smaller than a traditional atom. He also concluded that every atom had these. These small particles were later named electrons. The plum-pudding model was a model showing the electrons surrounded by a soup of positive charge to balance the electrons negative charge. The negatively charged electrons (plums) were surrounded by positively charged “pudding.” -
Robert Millikan Experiment
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Robert Milliken-He measured the charge on an electron in 1909.
The experiment he used was the oil-drop experiment. This experiment started out with him spraying a mist of oil droplets into the upper chamber. He would let them fall until they reached terminal velocity due to air resistance. Then, he applied a charge to the falling drops by irritating the bottom chamber with X-Rays. Then, he attached a battery between the plates that would act on the oil drops. The electrons were still in the air when the magnetic field fired up. -
Ernest Rutherford-In 1911, he made his second important discovery, the nuclear model of of the atom.
With his new discovery, he built off of that discovery and made his third important discovery, the splitting of the atom. The experiment that he did was shooting alpha particles onto gold foil, and when he analyzed the results in 1911, he disproved J.J. Thomson due to the atom having a central charge. -
Ernest Rutherford Experiment
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Niels Bohr Experiment
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NIels Bohr-He joined with Rutherford in 1912 and slightly tweeked Rutherford’s model and released the Rutherford-Bohr model of the atom in 1913.
Bohr determined that based on all laws of classical physics, that the paths should be very unstable. He suggested that the revolutionary idea that electrons “jump” between energy levels or “orbits,” in a quantum fashion, that never exists in an in-between state. He basically believed that the electrons in the outer shell revolved around the nucleus like the planets orbit the sun, but with electrostatic forces instead of gravity. His experiments involved the Rydberg formula and explaining the spe -
James Chadwick-In the year 1932, he proved the existence of the neutron.
When he studied under Ernest Rutherford, he began to study beta radiation. Using Geiger’s counter, he was able to demonstrate that beta radiation was produced a continuous spectrum and not discrete lines as previously thought.
The experiment he conducted was he would emit radiation through Beryllium and studied the particles released and that is where he discovered the neutron. Then, he sent those neutrons through Paraffin Wax to produce protons that were sent into an ionization chamber. -
James Chadwick Experiment
