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Benjamin Franklin
Franklin Discovered that electrical charges come in 2 varieties – positive and negative. Like charges repel, opposite charges attract. He imagined charge as a type of invisible fluid that was in all substances and matter. Franklin also believed that when rubbing two substances together, the fluid would change location. Source: https://en.m.wikipedia.org/wiki/Electric_charge -
Joseph Louis Proust
Proust created the Law of Definite Proportions, sometimes called The Law of Constant Composition, states that a chemical compound always contains exactly the same proportion of elements by mass. H2O always contains 88.9% O, 11.1% H by mass. Proust studied copper carbonate, the two tin oxides, and the two iron sulfides to prove this law. He did this by making artificial copper carbonate and comparing it to natural copper carbonate.
Source: https://en.m.wikipedia.org/wiki/Joseph_Proust -
William Crookes et. al.
A. Cathode Ray Tube (CRT)
CRT – a glass tube that is evacuated (contains no air or matter) coated with fluorescent paint. When connected to a battery, the paint glows, indicating that there is some type of radiation streaming from the battery (the cathode).
B. Paddle wheel placed in CRT:
When Crookes placed a paddle wheel in the CRT and turned on the battery, the wheel spun. Since the tube was evacuated, this told Crookes that the Cathode Ray has mass. -
Sir John Joseph Thomson
A. Continued experimenting on the CRT:
JJ Thomson used charged plates to deflect the cathode ray. Found the ray deflected away from the negative plate, and toward the positive.
B. Deduced that the cathode ray was made of: Negative particles. He named them electrons. -
Period: to
Ernest Rutherford Part 1
A. Classification of radiation
B. Famous Gold Foil Experiment
1. What he did:
Stretched a sheet of gold foil in a tin can and coated the inside of the can with fluorescent paint.
Aimed a ray of alpha radiation (+ charges) at the foil.
Expected that the alpha rays would pass right through the metal atoms in the foil, and the fluorescent coating would light up right behind the foil. -
Curies (Marie and Pierre)
Discovered and isolated polonium and radium from uranium ores.
The study of radioactive elements (elements that spontaneously change into different elements due to instability) gave scientists the inkling that there had to be something inside the atom that gave it its identity, and that if that thing changed, the atom would change or “transmute” into another element. -
Antoine Henri Becquerel
Discovered radioactivity in Uranium ore. -
Robert Andrews Millikan
Calculated the mass and charge of an electron. -
James Chadwick
Proved the existence of another subatomic particle, that had no charge, named it the neutron.
