Bonjour, j'aimerai être aidée à propos d'un DM sur John Dalton en anglais:


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
   Nitrogen 5    
  Carbon 5.4  
   Oxygen 7    
  Phosphorus 9  
   Sulphur 13    
  Magnesia 20  
   Lime * 24    
   Soda 28    
  Potash 42    
   Strontium 46    
   Barium 68    
  Iron 50    
  Zinc 56    
  Copper 56    
  Lead 90    
  Silver 190  
    Gold 190    
  Platinum 190  
   Mercury 167


(* 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”)

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?