How do we know that matter consist of atom?

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Homework Statement



How do we know that matter consist of atom?

Homework Equations





The Attempt at a Solution

 
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The number of atoms or molecules in a given amount of substance is related by Avogadro's Number. What ways exist of determining it?
 
If I remember correctly, it was John Dalton who first proposed the existence of atoms. Read up on how he came to that conclusion. The word 'valency' comes into it.
 
AJ Bentley said:
If I remember correctly, it was John Dalton who first proposed the existence of atoms. Read up on how he came to that conclusion. The word 'valency' comes into it.

(Well, if you discount the Greeks..) But valency doesn't come into Dalton's rationale, actually. (It wasn't a known concept during his lifetime, even.) Dalton had found the "law of fixed proportions"; that chemical elements appeared to react and combine in certain fixed proportions, which the atomic hypothesis explained.

But it wasn't until the Karlsruhe congress of 1860 that the hypothesis was generally accepted among chemists, (but not among contemporary physicists, notably Ernst Mach). It wasn't until Jean Perrin's 1913 book "Les Atomes" that the last die-hards were convinced.
 
alxm said:
But valency doesn't come into Dalton's rationale

He didn't use the word, granted. I was merely laying a crumb trail for the OP to follow.
 
Or look up STM images on google :)
 

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