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Chapter 3 “Atomic Structure”

or,

“How did we get here from there?”

Sept. 2006

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OBJECTIVES

• Define the term “atom.”• Review the early history of

Atomic Theory.• List the postulates of Dalton’s

Atomic Theory.

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“A Brief History of Chemistry”by Mr. Matt Davis & Dr. Tom Witherup

• Ancient Greeks were the first we know about to record ideas about chemistry.

• Plato and Aristotle, the philosophers, believed there were four “elements”:– Earth, air, fire & water.– Each had a unique shape (cube, octagon,

tetrahedron & icosahedron).– Everything was made from these ‘elements.’

• These ideas were not tested, though.– What does this show about the power of “The

Establishment”?

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The Greek philosopher, Democritus, was a ‘rebel’ who was the first to use the word “atom.”

“All matter are indivisible atoms or ’the void.’”

Since he was also a philosopher, not an explorer, he did not do any experiments. He was a …..

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“Thinker!”

(Who was the sculptor?)

Auguste Rodin

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•D

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More History…

• The Greeks fell to the Romans.• Then the Romans fell as well.

• Why?

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The Fall Of the Roman Empire

•Did civil wars lessen the strength of the empire and weaken the population? •Did the army lose its discipline, thus endangering the empire and causing it to be overrun by barbarians? •Did the citizens of Rome become too satisfied and lazy, allowing the empire to crumble due to neglect? •Did the empire’s bureaucracy become too top heavy, eventually causing the empire to collapse upon itself? •Did God turn His favor away from Rome due to its sinful ways? •Did the empire spend too much of its resources on the poor, thus drawing away precious funds from the empire? •Was the Roman Empire itself just too big to govern, making a collapse inevitable? •Did plagues reduce the population to the point that it could not sustain itself?

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No, the reason for the fall of Rome was, of course,

“chemistry”!

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What was it? Lead Poisoning!

• Gilfillan, S. Colum, “Rome's Ruin by Lead Poison,” Wenzel Press, Long Beach, CA, 1990.

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Lead Poisoning in Rome

• Lead is a very soft metal, so it was used to easily make water pipes and drinking vessels.

• Lead compounds were also added to wine to sweeten it. (“Sweet Sugar of Lead”)

• The Romans didn’t know they were poisoning themselves.

• Footnote: Sadly, nearly 1 million children in the United States today have blood lead levels that are high enough to cause irreversible health damage. But lead poisoning is entirely preventable. How? – Use lead-free gasoline, paints and other products.

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Then came the

Dark Ages.

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The Dark Ages, a time of …

• Feudalism.• Ignorance.• Disease.• Survival of the fittest.

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To the rescue came the “Alchemists.”

• These were Medieval experimenters.

• They tried to turn lead into gold.

• By accident, they learned much about the nature of chemistry!

• Islamic alchemists invented many lab techniques still in use.

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•DA

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Later, in the Age of Enlightenment, Antoine Lavoisier proposed…

• The Law of Conservation of Mass. • "Nothing is created, either in the

operations of art or in those of nature, and it may be considered as a general principle that in every operation there exists an equal quantity of matter before and after the operation.”

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Antoine Lavoisier (1743 - 1794)

Text p.73 shows his experiment. He invented a very accurate & precise analytical balance. How did he ignite the candle?

Sadly, Lavoisier was beheaded during the ‘Reign of Terror.’

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•DAL

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At about the same time, Joseph Louis Proust

proposed…

The Law of Definite Compositions.

“The proportion by mass of the elements in a given compound is always the same.”

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Joseph Louis ProusT (1754 – 1826)

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But a controversy arose between ProusT and Claude

BertholleT.

• Each announced contradictory laws around 1800.

• Proust: Elements combine to form compounds in a fixed proportion by weight.

• Berthollet: Elements combine to form compounds in variable ratios.

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•DALT

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Along came Amedeo

Avogadro who suggested…

• “Equal volumes of all gases at the same temperature and pressure contain the same number of molecules.” (Avogadro's Principle) (1776 – 1856)

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Along came Amedeo

Avogadro who suggested…

• “Equal volumes of all gases at the same temperature and pressure contain the same number of molecules.” (Avogadro's Principle) (1776 – 1856)

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•DALTO

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In the meantime, someone dusted off the works of Francis BacoN (1561-

1626) who published…

• “The Scientific Method”

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Putting it all together was…

•DALTON

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.DALTON

John Dalton (1766 – 1826)

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Dalton’s Atomic Theory (1803)

• Elements are made of tiny indestructible atoms.• Atoms of a given element are identical.• Atoms of different elements have different

masses and properties.• Atoms only combine in small, whole number

ratios such as 1:1, 1:2, 2:3, etc.• Chemical reactions are the rearrangements of

atoms.• Atoms are neither created nor destroyed in

chemical reactions.

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Most of Dalton’s Atomic Theory survived the ‘test of time,’ except…

• Elements are made of tiny indestructible atoms.– We now know that nuclear explosions actually

destroy atoms, releasing energy by Einstein’s famous equation, E = mc2.

• Atoms of the same element are identical, with the same properties (including their weight).– We now know this is incorrect, but in 1803 the

concept of isotopes was still over 100 years in the future.

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Did we meet the OBJECTIVES?

• Define the term “atom.”• Review the early history of

Atomic Theory.• List the postulates of Dalton’s

Atomic Theory.

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Let’s pause here to acknowledge some other people who contributed

to the Atomic Theory, such as…• Michael Faraday (1791 - 1867)• Benjamin Franklin (1706 - 1790)• J. J. Thomson (1856 - 1940)• Robert Millikan (1868 - 1953)• Henri Becquerel (1852 - 1908)• Marie Curie (1867 - 1934) & Pierre Curie (1859

- 1906)• Ernest Rutherford (1871 - 1937)• James Chadwick (1891 – 1974)• Henry Moseley (1887 - 1915)• We will learn about their important

contributions next.

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Let’s pause here to acknowledge some other people who contributed

to the Atomic Theory, such as…

• Michael Faraday (1791-1867)• Benjamin Franklin (1706-1790)• J. J. Thomson (1856-1940)• Robert Millikan (1868-1953)• Henri Becquerel (1852-1908)• Marie Curie (1867-1934) & Pierre Curie (1859-

1906)• Ernest Rutherford (1871-1937)• James Chadwick (1891 – 1974)• Henry Moseley (1887-1915)• We will learn about their work next.