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Chemistry 125: Lecture 20
Rise of the Atomic Theory (1790-1805)
Elemental analysis was the technique for determining the composition of organic
compounds. Lavoisier's early combustion and fermentation experiments showed a new,
though naïve, attitude toward handling experimental data. Dalton’s atomic theory was
consistent with the empirical laws of definite, equivalent, and multiple proportions. The basis
of our current notation and of precise analysis was established by Berzelius, but confusion
about atomic weight multiples, which could have been clarified at the outset by accepting
the suggestions of Avogadro and Gay-Lussac, would persist for more than half a century.
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For copyright notice see final page of this file
Elementary Treatiseof Chemistry
1789
PRESENTED IN A NEW ORDERAND ACCORDING TO MODERN DISCOVERIES
With Figures
How to analyze a substance that will not burn cleanly?
e.g.grape sugar
Everyone knows how wine, cider and mead are made…
Plate X: Fermentation Apparatus
H2OAbsorptionby CaCl2
CO2
Absorption by NaOH soln.
any other Gas
Foam catcher
Sugar/Yeast/Water
I can consider the materials subjected to fermentation and the products of fermen-tation as an algebraic equation; and by in turn supposing each of the elements of this equation to be unknown, I can derive a value and thus correct experiment by calculation and calculation by experi-ment. I have often profited from this way of correcting the preliminary results of my experiments.
Fermentation
it can furnish a meansof analyzing sugar
Oxidation failed withair
oxygensulfuric acid
mercuric oxideetc.
because of incomplete combustion (charring)
Hydrogen GeneratorRed-hot Glass Tube
Water
28 grains Carbon
Water
Water (less 85.7 grains)
144 cu. in. (100 grains) Carbonic Gas380 cu. in. (13.7 grains) Flammable Gas
Carbon + Water 28 gr. 85.7 gr.
= Carbonic Gas + "Hydrogen" 100 gr. 13.7 gr.
"I have thought it best to correct by calculationand to present the experiment in all its simplicity."
157
313
103
9.4from 28 gr. C
(modern theory) ………
?+ += !
1.38 g
Traitépp. 88-92
Facts Ideas
Words
Lavoisier Contributions
Elements
Conservationof Mass
Oxidation
Radical/Acid
Salts
Apparatus
QuantitationMassvolume
Substances
Reactions
Meaningful NamesElement - Oxidation State - Salt Composition
-ous, -ic, -ide, -ite, -ate
Clarity
[Chemistry's] present progress, however, is so rapid, and the facts, under the modern doctrine, have assumed so happy an arrangement, that we have ground to hope, even in our own times, to see it approach near to the highest state of perfec-tion of which it is susceptible.
Lack of Imagination
"Il ne leur a fallu qu’un moment pour faire
tomber cette tête, et cent années peut-être ne suffiront pas pour
en reproduire une semblable."
"It took them only an instant to make
this head fall, but a hundred years
may not suffice to reproduce one like it."
Lavoisier Guillotined May 8, 1794 Age 50
"The Republic has no need of geniuses.”
But all of his equipment (including 80 pounds of mercury)
was seized for The People.
John Dalton
Why do gases of different density remain mixed rather
than stratifying?
amateur meteorologist
1801
Continental European scientists proposed that different gases attract one another.
"the atoms of one kind did not repel the atoms of another kind"
Atom“Heat Envelope”
Match
Repulsion
Mismatch
Reduced
Repulsion
Substituteshomorepulsion
for heteroattraction
Atoms Explain:
Definite Proportions
Equivalent Proportions
Multiple Proportions
Pure compounds always have the same weight ratio of their elements.
If a parts of A react with b parts of B,and a parts of A react with c parts of C,…
If two elements form several compounds,their weight ratios are related by simple factors.
and d parts of D react with b parts of B,then d parts of D react with c parts of C.
Definite Proportions?
Joseph Louis PROUST(1754-1826)
Claude Louis BERTHOLLET
(1748-1822)
NON! OUI !
metal alloysnatural "organic" materials
"chemicals"
Multiple Proportions
O/C
2.57
1.27
O/N
0.58
1.27
2.39
Oxides of Carbon %C %O
28 72
44 56
Carbonic Acid (1801)
Carbonous Acid (1789)
Oxides of Nitrogen %N %O
63.30 36.70
44.05 55.95
29.50 70.50
Nitrous Oxide (1810)
Nitrous Gas (1810)
Nitric Acid (1810)
[1]
~22.19
~44.12
~22.02
[1]
Rel.
Rel.
integral values consistent with simple atomic ratios%err
of (O/C)vs. modern
-4
-5
-2
+11
+11
%errof (O/N)vs. modern
BerzeliusJöns-Jakob
BERZELIUS(1779-1848)
Organic & Mineral
Analysis
Dualism(double decomposition)
Electrolysis
Notation forComposition
Teaching& Writing
Textbook(1808)
2000 compounds in 6 years!
Good Atomic Weightsfor 50 elements!
“When only one combination of two bodies can be obtained, it must be pre-sumed to be a binary one, unless some other cause appear to the contrary.”
ChemicalSymbolsof 1774(Sweden)
HO HN NO HC OC
N2O NO2 CO2 CH2
H N C O P S Mg CaNa K Sr Ba Fe Zn Cu Pb
Ag Pt Au Hg(Corresponding Berzelius Symbols)
Dalton Notation(1808)
http://webserver.lemoyne.edu/faculty/giunta/dalton.html
NO3 SO3 SH3 C3H
“When four…one binary, two ternary, and one quarternary, &c.
Latin (international)
Analytical (NOT structural)
Berzelius Notation(1811)
Dalton’s Logic
N2O NO2 CO2 CH2
NO3 SO3
SH3 C3H
When three…a binary, and the other two ternary. ”
“When two combinations are observed, they must be presumed to be a binary and a ternary…
Abbreviations: Dots denote O atoms
= KO CrO3
Superscripts denote numbers of atomsBenzoic should be H10C14O3 (“acid” as anhydride)
Didn’t catch on
•
Dalton’sAtomic Weights
(1808) Weights
15579
13
HCNOPS
2004
11214163132
/1 /2 /3 /2 /3 /2
% err
9 9
16 5 5
12
Joseph Louis Gay-Lussac(1809)
Oxidation of Sugar, etc. with NaClO3
Cleans up Lavoisier's Mass Balance
1.9989 volumes of hydrogen per
1.0000 volumes of oxygen Water gives
3.08163 volumes of hydrogen per
1 volume of nitrogen Ammonia gives
Alternative to Dalton's Law of Greatest Simplicity
1804 - 7,016 m(record for 50 years)
(1778-1850)
Established thatatmospherecompositionis invariant
with altitude.
End of Lecture 20Oct. 22, 2008
Copyright © J. M. McBride 2009. Some rights reserved. Except for cited third-party materials, and those used by visiting speakers, all content is licensed under a Creative Commons License (Attribution-NonCommercial-ShareAlike 3.0).
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