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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. -
Period: 384 BCE to 322 BCE
Aristotle
Refuted Democritus
Believed in four elements: Earth, Air, Fire, and Water.
Aristotle’s refutation of Democritus’ Atomic Theory led to nearly 2000 years of bogus “science” Among the most prominent: -
Period: 300 BCE to 500
Alchemy Part 1
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. -
Period: 600 to 700
Alchemy Part 2
Arabs occupied Egypt and further developed the science, spread it to the West (Spain) in 700s.
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 -
Period: 1500 to
Alchemy Part 3
the alchemists in Europe had separated into two groups:
western alchemists focused on the discovery of new
compounds, reactions, and chemical processes - leading to what is now the science of chemistry. 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 transmutation of base metals into gold. This
led to the modern day idea of alchemy. -
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"
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 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.
H2O always contains 88.9% O, 11.1% H 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. -
Period: to
William Crookes et. al.
A. 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).
B. 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
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. -
Period: to
Ernest Rutherford Part 1
A. Classification of radiation
B. 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. -
Becquerel
Discovered radioactivity in Uranium ore. -
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: 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: A. Atoms are mostly empty space. B. There must be a solid core in the center of the atom. C. The core must be positively charged, since it deflected an alpha ray.
-
Milikan
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.