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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Elementary Treatiseof Chemistry

1789

PRESENTED IN A NEW ORDERAND ACCORDING TO MODERN DISCOVERIES

With Figures

Oxidation States

Radical1°

"oxide"2°

"-ous" acid3°

"-ic" acid

4°"oxygenated

-ic" acid

Elemental Analysis by Oil Combustion

Air Supply

LampOil

Supply

H2OCollector

CO2

Collector

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)

Lavoisier’s Bookkeeping

72 grains = 1 gros8 gros = 1 ounce = 28.35 g

Lavoisier’s Bookkeeping

Lavoisier’s Bookkeeping

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.

Boyle Lavoisier√

√

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

Genealogy Top

Berzelius etc.

√

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!

Notation for Composition

Alchemy

Dalton

Berzelius

ChemicalSymbolsof 1774(Sweden)

1774 Symbols

“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

Atomic Weights and Equivalents

•

Dalton’sAtomic Weights

(1808) Weights

15579

13

HCNOPS

2004

11214163132

/1 /2 /3 /2 /3 /2

% err

9 9

16 5 5

12

Silicon ChlorideSiCl T. Thomson

SiCl2 L. Gmelin

SiCl3 J. J. Berzelius

SiCl4 Wm. Odling?

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

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