Transcript history of atomic theory (ending with Dalton)

1
Chapter 3 “Atomic Structure”
or,
“How did we get here from
there?”
Sept. 2006
2
OBJECTIVES
• Define the term “atom.”
• Review the early history of
Atomic Theory.
• List the postulates of Dalton’s
Atomic Theory.
3
“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”?
4
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 …..
5
“Thinker!”
(Who was the sculptor?)
Auguste Rodin
6
•D
7
More History…
• The Greeks fell to the Romans.
• Then the Romans fell as well.
• Why?
8
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?
9
No, the reason for the fall of
Rome was, of course,
“chemistry”!
10
What was it? Lead Poisoning!
• Gilfillan, S. Colum,
“Rome's Ruin by Lead
Poison,” Wenzel Press,
Long Beach, CA, 1990.
11
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.
12
Then came the
Dark Ages.
13
The Dark Ages, a time of …
• Feudalism.
• Ignorance.
• Disease.
• Survival of the fittest.
14
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.
15
•DA
16
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.”
17
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.’
18
•DAL
19
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.”
20
Joseph Louis ProusT (1754 – 1826)
21
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.
22
•DALT
23
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)
24
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)
25
•DALTO
26
In the meantime, someone dusted off
the works of Francis BacoN (15611626) who published…
• “The Scientific Method”
27
Putting it all together was…
•DALTON
28
N
.DALTO
John Dalton (1766 – 1826)
29
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.
30
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.
31
Did we meet the OBJECTIVES?
• Define the term “atom.”
• Review the early history of
Atomic Theory.
• List the postulates of Dalton’s
Atomic Theory.
32
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.
33
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 (18591906)
Ernest Rutherford (1871-1937)
James Chadwick (1891 – 1974)
Henry Moseley (1887-1915)
We will learn about their work next.
34