DNL Physique 1èreS. Science History, chemistry
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Science History
October, 23rd, 1803 : a great day for Chemistry
John Dalton presented an essay on the absorption of gases by water, at the conclusion of which he
gave a series of atomic weights for 21 elements. He read his paper at a meeting of the Manchester Literary
and Philosophical Society. John Dalton is now called the father of modern atomic theory for his efforts.
"A series of Essays read before this society and afterwards published in the 5th
Vol. of their Memoirs gradually led me to the consideration of ultimate particles or
atoms & their combinations. […] On the 23rd of October the same year [I] [r]ead my
Essay on the absorption of gases [by water] at the conclusion of which a series of
atomic [weights] was given for 21 simple […] elements…"
John Dalton
(Excerpt from paper read to Manchester Literary and Philosophical Society, 1830)
In September of 1803, John Dalton wrote his first table of atomic weights in his daily
logbook. In October, he stated his most well-known quote… in front of seven auditors.
Two years after he developed his atomic weights, he published them in a book called
"A New System of Chemical Philosophy”. In it he was the first to propose that elements should be identified
with symbols. However, only 3 or 4 pages in the third chapter discussed the atomic theory he proposed. In this
theory, there are five basic ideas:
1) Chemical elements are made of atoms.
2) The atoms of an element are identical in their masses
3) Atoms of different elements have different masses
4) Atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3 and so on.
5) Atoms can be neither created nor destroyed
Here are the first elements symbols introduced by Dalton, and the atomic weights he proposed, taking hydrogen
as a reference:
Hydrogen 1
Lime * 24
Copper 56
Nitrogen 5
Soda 28
Lead 90
Carbon 5.4
Potash 42
Silver 190
Oxygen 7
Strontium 46
Gold 190
Phosphorus 9
Barium 68
Platinum 190
Sulphur 13
Iron 50
Mercury 167
Magnesia 20
Zinc 56
(* known today as Calcium)
(2 interesting facts: the unit for atomic weight was called a "dalton" for many years. Today, it is used in
biochemical circles, (e.g. "The atomic weight of that protein is 35,000 daltons."); Dalton also studied himself :
he was not able to see some colours : this illness, called dyschromatopsy, is now well-known as “daltonism”)
ANG LYC DIV CHI 106753661
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DNL Physique 1èreS. Science History, chemistry
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Questions :
1) Who was the first scientist to introduce atomic theory, long before Dalton?
2) Are the 5 basis of Dalton’s theory right? Give examples (or counter-examples)
3) Was Dalton able to prove his theory by experiments? Do you know a famous experiment proving the
existence of atoms?
4) The measures made by Dalton were quite precise for his century, even if now they have been improved.
With your chemistry book, calculate the % of error he made for platinum and iron.
5) What system is now used to symbolize elements? Give the symbols of elements known by Dalton.
Which famous chemist completed Dalton’s work to give it the aspect we know today?
ANG LYC DIV CHI 106753661
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