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Period: 460 BCE to 370 BCE
Democritus
Atomos: that which cannot be cut
Definition of Atom: the smallest unit of matter which still retains the identity and properties of that matter
Many consider Democritus to be the "father of modern science" -
384 BCE
Aristotle
Aristotle proved Democritus’ theory wrong which led to 2000 years of bogus science. Aristotle also believed in the four elements Earth, Air, Fire, and Water. -
Period: 300 BCE to 500
Alchemy
332 BC Alexander the Great had conquered Egypt
Greek philosophers became interested in the Egyptian religion. Greek views of how matter is made up of the four elements of nature were merged with Egyptian religion.
The result was Khemia, the Greek word for Egypt.
The word Alchemy came from the word Khemia, which means Egypt.
Alchemy covers several philosophical traditions spanning some four millennia and three continents.. -
Period: 600 to 700
Alchemy #2
The start of Western alchemy may generally be traced to ancient and Hellenistic Egypt, where the city of Alexandria was a center of alchemical knowledge, and retained its pre-eminence through most of the Greek and Roman periods
600 A.D. Arabs occupied Egypt and further developed the science, spread it to the West (Spain) in 700s. -
Period: 1500 to
Alchemy #3
Metals are made up of mercury and sulfur in varying proportions.
Gold is the perfect metal and all others were “Baser” metals, capable of being transmuted into gold by means of a substance known as the Philosophers Stone.
Alchemists applied this concept of purification and search for perfection to the human condition, and sought spiritual purification and immortality
Eventually, by the 16th Century, the alchemists in Europe had separated into two groups -
Alchemy #4
In the west, alchemists focused on the discovery of new compounds, reactions, and chemical processes - leading to what is now the science of chemistry. -
Period: to
Vitalism
Living organisms are fundamentally different from non-living entities because they contain a “vital spirit”.
Living things are thus governed by different principles than are inanimate things.
Biologists now consider vitalism to have been refuted by empirical evidence, and hence as belonging to the realm of religion rather than that of science. -
Period: to
The phlogiston
from the Ancient Greek phlogistón "burning up"
first stated in 1667 by Johann Joachim Becher
postulated the existence of a fire-like element called "phlogiston", which was contained within combustible bodies and released during combustion.
A substance that burned did so because it contained Phlogiston.
Carbon Dioxide, no longer capable of burning was called “dephlogisticated air” -
Period: to
Anton Laurent de la voisier
Father of Modern Chemistry because he relied on quantitative observation to develop conclusions.
Dispelled the Phlogiston Theory by proving that Oxygen causes combustion.
Discovered the Law of Conservation of Mass: By proving that the mass of a metal oxide = the mass of the metal plus oxygen when the metal oxide decomposes.
Matter can change form, but cannot be created nor destroyed in a chemical reaction.
Beheaded during French Revolution -
Benjamin Franklin
Discovered that electrical charges come in 2 varieties – positive and negative. Like charges repel, opposite charges attract. -
Joseph Louis Proust
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. -
Period: to
John Dalton: Father of atomic theory
Matter is made up of atoms that are indivisible and indestructible.
All atoms of an element are identical. (Known now to be untrue!)
Atoms of different elements have different weights and different chemical properties.
Atoms of different elements combine in simple whole numbers to form compounds.
Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged. -
Period: to
William Crookes et. al.
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)
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
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.
Deduced that the cathode ray was made of:
Negative particles. He named them electrons. -
Period: to
Ernest Ruthford
@ 1900: Classification of radiation
@ 1910: 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. -
Period: to
Ernest Rutherford
- What he observed:
- 99.9% of the time, the ray lit up the can right behind the foil.
- .1% of the time, the ray lit up the can OPPOSITE the foil. (behind the alpha source)
- This told him that the ray had hit something massive and dense in the center of the atom.
- What he deduced: Atoms are mostly empty space. There must be a solid core in the center of the atom. The core must be positively charged, since it deflected an alpha ray
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Becquerel
Discovered radioactivity in Uranium ore. -
Curies (Marie and Pierre)
Discovered and isolated polonium and radium from uranium ores. -
Milikan
Calculated the mass and charge of an electron
Robert Andrews Millikan was an American experimental physicist honored with the Nobel Prize for Physics in 1923 -
James Chadwick
Discovered the neutron
Won Nobel Prize in 1935
In 1941, he wrote the final draft of the MAUD Report, which inspired the U.S. government to begin serious atomic bomb research efforts.
He was the head of the British team that worked on the Manhattan Project during the Second World War.
He was knighted in England in 1945 for his achievements in physics.