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Period: 460 BCE to 370 BCE
Democritus
Atomos: that which cannot be cut.
Atom: the smallest unit of matter which still remains the identity and properties of that matter. -
Period: 384 BCE to 322 BCE
Aristotle
Believed in four elements: Earth, Fire, Air, and Water. -
332 BCE
Alexander the Great
Conquered Egypt -
600
Expansion of Alchemy
Alchemy in Egypt spread in to the West (Spain) in 700s -
Alchemists of Europe
The alchemists in Europe has separated into two groups In the west, alchemists focused on the discovery of new compounds, reactions, and chemical processes. Invented Distillation, percolation, extraction, rudimentary chromatography. The second group continued to look at the more spiritual, metaphysical side of alchemy, continuing the search for immortality and the transformation of base metals into gold. -
Johann Joachim Becher
Postulated the existence of a fire-like element called “phlogiston,” which was contained within combustible bodies and released during combustion Known as the “The Phlogiston Theory” -
Period: to
Anton Laurent de La Voisier
Father of Modern Chemistry
• Dispelled the Phlogiston Theory by proving that Oxygen causes combustion.
• Discovered the Law of Conservation of Mass.
• 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 two varieties – positive and negative. Like charges repel, opposite charges attract. -
Joseph Louis Proust
The Law of Definite Proportions:
OR
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
A. Matter is made up of atoms that are invisible and indestructible.
B. All atoms of an element are identical.
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 atom are recovered unchanged. -
Period: to
Ernest Rutherford
1900 — Classification of radiation
Three types of radiation
• Alpha
• Beta
• Gamma 1910 — Famous Gold Foil Experiment
Stretched a sheet of 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 through the metal atoms in the foil, and the fluorescent coating would light up right behind the foil. -
William Crookes
Cathode Ray Tube (CRT) - a glass tube that is evacuated (contains no air or matter) Coates 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 Crooks places a paddle wheel in the CRT and turned on the battery, the wheel spun. Since the tube was evacuated, this told Crooks that the Cathode Ray has mass. -
Sir John Joseph Thomson
Continued experimenting on the CRT: Used charged particles 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. -
Curies (Marie and Pierre)
Discovered and isolated polonium and radium from uranium ores. -
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.
