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Period: 460 BCE to 370 BCE
Democritus
He was an Ancient Greek philosopher born in Abdera, Thrace. He is remembered today for his formulation of an atomic theory of the universe. Atoms cannot be cut and are the smallest unit of matter which still retains the identity and properties of that matter. -
Period: 384 BCE to 322 BCE
Aristotle
Aristotle was an Ancient Greek philosopher. He founded his own school, the Lyceum, in Athens, where he spent most of the rest of his life studying, teaching and writing. He also believed in four elements earth, air, fire, and water. -
Period: 332 BCE to 323 BCE
Alexander The Great
During Alexander the Great conquered egypt Greek philosophers became interested in Egyptian religion and alchemy. Alchemy is based on the supposed transformation of matter. It was concerned particularly with attempts to convert base metals into gold or to find a universal elixir. -
Period: to
Anton Laurent de La Voisier
He is known as the Father of Modern Chemistry because he relied on quantitative observation to develop conclusions. Discovered the Law of Conservation of Mass. He dispelled the Phlogiston Theory by proving that Oxygen causes combustion. He was beheaded during the French Revolution -
Period: to
Benjamin Franklin
He discovered that electrical charges come in 2 varieties – positive and negative. Like charges repel, opposite charges attract. -
Period: to
Joseph Louis Proust
He was a French chemist. He was best known for his discovery of the law of constant composition in 1794, saying that chemical compounds always combine in constant proportions -
Period: to
John Dalton
He was an English chemist, physicist, and meteorologist. He is best known for introducing the atomic theory of matter into chemistry. He also researched color blindness. -
Period: to
William Crookes
Hewas a British chemist and physicist who attended the Royal College of Chemistry in London. 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). 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. -
Period: to
Sir John Joseph Thomson
He was an English physicist and Nobel Laureate in Physics. He continued to experiment CRT. Thomson used charged plates to deflect the cathode ray. Found the ray deflected away from the negative plate, and toward the positive. Negative particles. He named them electrons. -
Period: to
Becquerel
He Discovered radioactivity in Uranium ore. -
Period: to
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. -
Period: to
Millikan
He calculated the mass and charge of an electron -
Period: to
Ernest Rutherford
In 1910 he did the "Famous Gold Foil Experiment", from this experiment he had discovered that atoms are mostly empty space,there must be a solid core in the center of the atom, and the core must be positively charged, since it deflected an alpha ray. -
Period: to
James Chadwick
Proved the existence of another subatomic particle, that had no charge, named it the neutron.
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