-
460 BCE
Early Models of the Atom
Democritus
Atoms: that which cannot be cut.
Definition of Atom: the smallest unit of matter which still retains the identity and properties of that matter. -
384 BCE
Early Models of the Atom
Aristotle refuted Democritus. He believed in four elements: Earth, Fire, Air, and Water. Aristotle’s refutation of Democritus’ Atomic theory led to nearly 2000 years of bogus “science” among the most prominent. -
300 BCE
Alchemy
In 332 BC Alexander the Great had conquered Egypt. Greeek philosophers became interested in the Egyptian religion. Greek views of how matter is made up of four elements of nature were merged with Egyptian religion. The Greek work for Egypt is Khemia. The word Alchemy means Egypt and it came from Khemia. -
600
Alchemy part 2
Alchemists applied this concept of purification and search for perfection to the human condition, and sought spiritual purification and immorality. By the 16th century the alchemists separated in two groups. The west group focused on discovery of new compounds, reactions, and chemical processes. They invented distillation, percolation, extraction, and more. The other group looked at the more spiritual side of alchemy, they continued to look for immorality and changing base metals into gold. -
Vitalism
Living organisms are fundamentally different from non living things because they contain a “spirit”.
Living things rare goverened by different principles than inanimate things. -
Phlogiston Theory
From the Ancient Greek pholgiston “burning up”
First stated in 1667 by Johnann 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” -
Jospeh Priestley
Jospeh is credited with the discovery of oxygen. -
Father of Modern Chemistry
Anton Laurent de La Voisier relies on the quantitative observations to get a conclusion. He 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 an change form, but cannot be created or destroyed in a chemical reaction. Anton was beheaded during the French Revolution. -
Benjamin Franklin
Discovered that electrical charges come in two viarieties- positive and negative. Like charges repel, opposite charges attract. -
Joseph Louis Proust
The law of definite proportions, sometime 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 -
Father of Atomic Theory
John Dalton atomic theory of matter:
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 atoms are recovered unchanged. -
Thomas Graham
Graham worked on dialysis and diffusion of gases. He then studied followed based on his use of dialysis. His work with diffusion of gases became know as Graham’s law. -
Louis Pasteur
He made the process for pasteurization and he also created vaccines for rabies and anthrax. He also found an asymmetrical molecule structure on certain crystals. -
Dmitri Mendeleev
Dmitri created the elements table. He also worked on the capillarity of liquids and the spectroscope. -
Svante Arrhenius
He came up with the theory of the “greenhouse effect”. Svante also founded the science of physical chemistry. His theory explained the “ice age”, resulted in the “greenhouse effect.” -
William Crookes
A. Cathode Ray Tube
CRT- a glass tube that doesn’t contain air or material 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. -
Otto Hahn
“Father of Nuclear chemistry” is another name for Otto. He was one of the earlier men who worked on radioactivity and radiochemistry. He also discovered “applied radiochemistry”. -
Sir John Joseph Thomson
A. Continued the experiment on the CRT:
JJ Johnson 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. -
Becquerel
Discovered radioactivity in Urnaium ore. -
Curies (Marie and Pierre)
Discovered and isolated polonium and radium from uranium ores. -
Millikan
Calculated the mass and charge of an electron. -
Ernest Rutherford
1900: classification of radiation
1910: Famous Fold Foil Experiemtn
What he did:Stretched a sheet of golf foil in a tin can and coated the inside of a can with flourescent paint. Aimed a ray of alpha radiation or positive charges at the foil. Expected that the alpha rays would pass right through the metal atoms in the foil, and the flourescent coating would light up right behind the foil. -
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.
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 an atom.
C. The core must be positively charged, since it deflected an alpha ray. -
James Chadwick
Proved the existence of another subatomic particle, that had no charge. He named it the neutron.
