-
460 BCE
Democritus
-
Period: 460 BCE to 370 BCE
Democritus
Remembered today for his formulation of an atomic theory of the universe.
Atomos: that which cannot be cut.
Definition of Atom: the smallest unit of matter which still retains the identity and properties of that matter. -
Period: 384 BCE to 322 BCE
Aristotle
He proved Democritus wrong.
Believed in the four elements; Earth, Air, Fire, and Water.
Aristotle's refutation of Democritus' Atomic Theory led to nearly 2000 years of bogus "science". -
Period: 300 to 500
Alchemy Part 1
In 332 BC Alexander the Great had conquered Egypt.
Greek philosophers had become interested in the Egyptian religion. The Greek views on how matter is made up of the four elements of nature was eventually combined with Egyptian religion.
The outcome of this was Khemia, which is the Greek word for Egypt.
The word Alchemy came from the word Khemia. -
Period: 600 to 700
Alchemy Part 2
Metals are made up of mercury and sulfur in varying proportions.
Gold is the perfect metal and all others were “Baser” metals, which are 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 they sought for spiritual purification and immortality. -
Period: 1500 to
Alchemy Part 3
Eventually, by the 16th Century, the alchemists in Europe had separated into two groups:
In the West, alchemists focused on the discovery of new compounds, reactions, and chemical processes - leading to what is now known as the science of chemistry.
The group in the west invented distillation, percolation, extraction, and rudimentary chromatography.
The second group continued to look at the more spiritual, metaphysical side of alchemy, continuing the search for immortality. -
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. -
Period: to
The Phlogiston Theory
From the Ancient Greek phlogistón “burning up”.
It was 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”. -
Anton Laurent de La Voisier
-
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.
He was beheaded during the 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 Compositon, states that a chemical compound always contains exactly the same proportion of elements by mass.
H2O always contains 88.9% O, 11.1% H by mass. -
John Dalton: Father of Atomic Theory
-
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 (which is know 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 of destroyed. When a compound decomposes, the atoms are recovered unchanged. -
William Crookes
-
Period: to
William Crookes el.al
Cathode Ray Tube (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
He continued experimenting on the CRT. He used charged plates to deflect the cathode ray. He found that the ray deflected away from the negative plate, and towards the positive.
He deduced that the cathode ray was made of: negative particles (which he named electrons). -
Period: to
Ernest Rutherford Part 1
A. Classification of radiation
B. Famous Gold Foil Experiment
What he did:
1. Stretched a sheet of gold foil in a tin can and coated the inside of the can with fluorescent paint.
2. Aimed a ray of alpha radiation (+ charges) at the foil.
3. 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. -
Becquerel
He discovered radioactivity in Uranium ore. -
The 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
Ernest Rutherford Part 2
What he observed:
1. 99.9% of the time, the ray lit up the can right behind the foil.
2. .1% of the time, the ray lit up the can OPPOSITE the foil (behind the alpha source).
3. This told him that the ray had hit something massive and dense in the center of the atom.
What he deduced:
1. Atoms are mostly empty space.
2. There must be a solid core in the center of the atom.
3. The core must be positively charged, since it deflected an alpha ray. -
Millikan
He calculated the mass and charge of an electron. -
Ernest Rutherford
-
James Chadwick
He proved the existence of another subatomic particle, that had no charge, and named it the neutron.
