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Period: 460 BCE to 370 BCE
Democritus
A. Atomos: that which cannot be cut
B. Definition of Atom: The smallest unit of matter which still retains the identities and properties of that matter. -
Period: 384 BCE to 322 BCE
Aristotle
Refuted Democritus. He believed in four elements: Fire, Water, Earth, and Air -
332 BCE
Alexander the Great had Conquered Egypt
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The Phlogiston Theory
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)
- 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
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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 proportions of elements by mass. -
Period: to
John Dalton (Father of Atomic Theory)
Dalton’s Atomic Theory of Matter:
A. Matter is made up of atoms that are indivisible and indestructible.
B. All atoms of an element are identical. (Known now to be untrue!)
C. Atoms of different elements have different weights and different chemical properties.
D. Atoms of different elements combine in simple whole numbers to form compounds.
E. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged. -
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. -
Ernest Rutherford
Classification of radiation -
Curies (Marie and Pierre)
Discovered and isolated polonium and radium from uranium ores. -
Becquerel
Discovered radioactivity in Uranium ore. -
Millikan
Calculated the mass and charge of an electron -
Famous Gold Foil Experiment
Done by Ernest Rutherford.
- 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. -
James Chadwick
Proved the existence of another subatomic particle, that had no charge, named it the neutron