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Period: 460 BCE to 370 BCE
Democritus
The discovery of atoms. The creation of their definition of “the smallest unit of matter which still retains the identity and properties of that matter.” -
Period: 384 BCE to 322 BCE
Aristotle
Refuted Democritus and believed in the four main elements, Earth, Air, Fire, and Water. This lead to years of “bogus” science. -
Period: to
Anton Laurent de La Voisier
Called the “Father of Modern Chemistry” because he relied on quantitative observation to develop conclusions. He proved that oxygen causes combustion. He discovered the Law of Conservation of Mass. -
Benjamin Franklin
He discovered that electrical charges come in 2 varieties – positive and negative. He also discovered that like charges repel, opposite charges attract. -
Joseph Louis Proust
He discovered the Law of Definite Proportions, sometimes called The Law of Constant Composition, which states that a chemical compound always contains exactly the same proportion of elements by mass. -
Period: to
John Dalton
Known as the “Father of Atomic Theory.” His theory was that, matter is made up of atoms that are indivisible and indestructible, all atoms of an element are identical, atoms of different elements have different weights and different chemical properties, atoms of different elements combine in simple whole numbers to form compounds, and that atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged. -
William Crookes
Invented the Cathode Ray Tube which is 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). -
Sir John Joseph Thomson
He used charged plates to deflect the cathode ray made by William Crookes. He found the ray deflected away from the negative plate, and toward the positive. He found that the Ray was made of negative particles. He named them electrons. -
Ernest Rutherford
Classified the different types of radiation. -
Becquerel
Discovered radioactivity in Uranium ore. -
Curies (Marie and Pierre)
Discovered and isolated polonium and radium from uranium ores. -
Millikan
Calculated the mass and charge of an electron. -
Ernest Rutherford
The gold foil experiment where he stretched a sheet of gold foil in a tin can and coated the inside of the can with fluorescent paint and aimed a ray of alpha radiation at the foil. He was expecting 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. What he found was that 99.9% of the time, the ray lit up the can right behind the foil and .1% of the time, the ray lit up the can opposite the foil. -
James Chadwick
Discovered another subatomic particle that had no charge. He named it the neutron.
