The History of the World

From a “chemist’s” view

The Father of Atomic Theory?

• Democritus• Atoms• ~400’s BCE

Aristotle

• Earth• Wind• Fire• Water

All substances were combinations of elements and elemental qualities. The elements are: fire, water, earth, and air. (Aristotle added later another "element" - Ether which was a perfect substance an what the heavenly bodies are composed of) The qualities are: hot, cold, wet, dry. The qualities define the character of "elements". Fire was seen as ideal mixture of hotness & dryness. One element could be changed into another like mixing solutions.

What is this guy’s occupation?

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Copernicus

Galileo

George Stahl

• Charcoal leaves little residue upon burning because it is nearly pure phlogiston.

• Mice die in airtight space because air saturates with phlogiston.

• When heated, metals are restored because phlogiston transferred from charcoal  to calx

• Metals get heavier when heated because phlogiston has a negative mass..

Joseph Priestly

• Discovered dephlogisticated air

• Contemporary of Franklin and Jefferson

• Isolated eight kinds of “airs.”

"Nothing is lost, nothing is created, everything is transformed." Antoine-Laurent de Lavoisier

• Law of Conservation of Matter

• In what historical event did he die?

• FATHER OF MODERN CHEMISTRY!!

John Dalton• elements consisted of tiny

particles called atoms.

• all atoms of an element were identical and that in particular they had the same mass.

• atoms of each element were different from one another; in particular, they had different masses.

• compounds consisted of atoms of different elements combined together.

• Compounds have constant composition because they contain a fixed ratio of atoms

• chemical reactions involved the rearrangement of combinations of those atoms.

Law of Multiple Proportions

When two elements form two different compounds, the ratio of the mass one element in compound A to that of the same element in compound B, will occur in small whole numbers.

Goldstein3. Canal rays (or positive rays)

1) Goldstein's experiment

Fig. The distinctive feature of this tube is the perforated cathode. Cathode rays stream towardsthe anode. Their collisions with residual gas atoms dislodge electrons from the atoms, producingpositively charged ions. These ions are attracted to the cathode (–), but some of the ions passthrough the holes in the cathode and appear as a stream of p articles on the other side. Thesebeams of positive ions are called positive rays or canal rays.

cathode raypositive rayhigh voltage power

J J Thomson

• Cathode Rays

• Cathode Rays are electrons

J.J. Thomson in his study (1899)

JJ at 78

THE EXPERIMENT

Earnest Rutherford

How can we describe the inside of an atom?

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Robert Millikan

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The END

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How are the electrons arranged?