[Unregistered]

Hello, does anyone know however scientists managed to prove at the time we splited water in dihydrogen and oxygen, that some substances were not molecules but unsplitting atoms?
At this time, I don't believe they used very technical means to end to that conslusion.
And yet what it's teached in high school doesn't prove anything, my classmates nodded, damn it's not catechism !
My problem is that I see all that haven't been proved to myself, as questionable.
I'm always wondering how did they do ? How could we dispute it if nobody knows how they did ?
All I managed to find out in Internet is almost word for word the same thing inculcated in classroom.
What an elite of thinkers they've made ! School need deep reforms at least in my country! I'm fed up
buying and reading expensive books to fall on the same murky stuff. Please could someone help me before
I get into a nervous breakdown.

[Borek]

I am not sure I understand your question - but I think they have not proved it at the time, that was just the simplest explanation, one that get confirmed later.

[Unregistered]

Perhaps it had been a lame theory for a long time. But sooner or later it had to be proved, you can't get away with it .
If you had a new substance, (which you want) outcome from another and you had to prove you can't break it down longer,
that body is only compounded of the same sort of atom, no molecules, in order to work out the atom theory, how would you do ? Because all that list of elements which we can forecast stochiometric stuffs now, has been worked out from the certitude that
they were atoms and nothing else and necessarily before Mendeleiv was born and found rules for elements. So any help would be welcome. I will do more researches and tell them at the same time, maybe I've got a clue

[Unregistered]

How do we know the amount of atom in a mol ? what a headache, they used microscopes ? oO
My book just tells who's wrong and why. Awesome ! now I'd like to know why we are right ?

[savy2020]

How do we know the amount of atom in a mol ? what a headache, they used microscopes ? oO
My book just tells who's wrong and why. Awesome ! now I'd like to know why we are right ?

Well could you define what is a mole?
Then I'll answer you

[cth]

How do we know the amount of atom in a mol ? what a headache, they used microscopes ? oO
My book just tells who's wrong and why. Awesome ! now I'd like to know why we are right ?

Atoms can't be seen using an optical microscope.
I found a webpage http://www.westminster.edu/acad/sim/pdf/SDeterminingAvogadro_001.pdf that you may find interesting. 

[Unregistered]

Atoms can't be seen using an optical microscope.
I found a webpage http://www.westminster.edu/acad/sim/pdf/SDeterminingAvogadro_001.pdf that you may find interesting. 

Thank you cth, indeed that's interesting. Savy2020 first prepare your answer and maybe I will take trouble to explain you what is a mole. Finally I don't need to know, there will always be something I'd have to trust without being able to prove it or even understand anyway I hate chemistry for that, that's why I give up school 6 years ago. I don't believe you all ! However I've got the doublethink I can use knowledge even so. Damn I'm drunk, I've found out that turtle heart still throbs when you cut it off, so cute ! I bet nobody knows how ATP has been discovered, they blindly trust !

[Borek]

http://lmgtfy.com/?q=determination+of+avogadro+number

[Unregistered]

Thank you Borek I know how google works !

[renge ishyo]

Unregistered, go get this book: "A Short History of Chemistry" by Issac Asimov. You can probably check it out from your library and read it in one or two afternoons. It will answer all your questions about who discovered what and how these discoveries led to our modern day conclusions...and it does so in a simple and elegant way.

The reality is that when these things were originally discovered things WERE very much up for debate. For example, when Dalton proposed the molecular formula for water he proposed that it must be HO. His evidence at the time led him to believe that. Later evidence concerning electrolysis of water led to the modification that made it H₂0 as there were two volumes of hydrogen gas released for every one volume of oxygen. Knowledge isn't built in a day, but over many years and we are continuing to refine our views. For this reason, short explanations of "how we know" are not possible. Asimov's book is the closest thing I have seen to a short answer to questions of this type.

[Unregistered]

Thank you renge ishyo, I will go and get this book. I've got one like that but it's rather biased towards industrialization. Two volumes of hydrogen released, Avogadro and Dalton were of the same generation, they might have worked together and discovered it sooner without electrolysis if it might occur their mind that water could be H2O. My first question is still unresolved, even if following experiences have merely confirmed the composition of substances as water, I still think that some major experiences have allowed us to define elements with certitude. I can't imagine scientists think "as far as we know, we haven't managed to decompose that stuff yet and in so far as we don't even know at all what it is, let's assert it's an element until detractors crop up" that sounds wrong. I just seek to gain an insight.
Have atoms got any testable property that molecules haven't ? oO

[Borek]

I can't imagine scientists think "as far as we know, we haven't managed to decompose that stuff yet and in so far as we don't even know at all what it is, let's assert it's an element until detractors crop up" that sounds wrong.

That's exactly how it worked. Some substances were considered elements before someone found a way to decompose them, or to show that they were in fact mixtures.

Have atoms got any testable property that molecules haven't ? oO

Yes, they can't be decomposed. That was the only property they were able to use.

[cth]

I can't imagine scientists think "as far as we know, we haven't managed to decompose that stuff yet and in so far as we don't even know at all what it is, let's assert it's an element until detractors crop up" that sounds wrong.

It is possible to prove that a theory is wrong by doing an experiment that directly contradicts it.
However, it is impossible to prove experimentally that a theory is right. You may do thousands of measures that prove it, yet you can't be absolutely sure the next experiment will confirm it...

To make it simple: scientist propose ideas, theoretical models... and check them in the lab. If all the experiments are conclusive, the theory is validated beyond reasonable doubts. For example, you have dead theories that were accepted for a long time, like the phlogiston http://en.wikipedia.org/wiki/Phlogiston but have been proved wrong.
An example of incomplete theory: Newton theory of gravitation has been working perfectly to describe motions from apples to planets... It was confirmed by countless measurements. And yet, it was incomplete, as shown by Einstein relativity. Similarly, relativity and quantum mechanics have been confirmed experimentally many many times. Yet, those two theory contradict each other when you try to use them together --> both are obviously incomplete as well. But the unifying theory has still to be worked out... So, we have to make do with those theory before getting a better one.

At best, a theory is only valid beyond reasonable doubts, not more:
- a good experiment is the one that invalidates your model, forcing you to move forward with a better one.
- a good scientist is someone who tries hard to break down his own theory and model! Not someone who tries to prove them.
The mindset of trying to break ones own work to see how robust it is, is not natural. As human, we would rather try to protect it. I see it as the main reason why religions (where you try to protect the dogma, no matter what) have been around for thousands of years while science is a new comer a few hundred years old.

[Borek]

It is possible to prove that a theory is wrong by doing an experiment that directly contradicts it.
However, it is impossible to prove experimentally that a theory is right. You may do thousands of measures that prove it, yet you can't be absolutely sure the next experiment will confirm it...

As Feynmann put it in his lecture - we can't be right, we can be only wrong

[Unregistered]

That's exactly how it worked. Some substances were considered elements before someone found a way to decompose them, or to show that they were in fact mixtures.

Seriously ?! But now we don't do that anymore concerning new substances, I hope ! Somehow we can check. Maybe not. It doesn't makes any sense I can't think that from them.
Phlogiston theory was a good theory except for the thousands of witches which must have served as measure, that's a shame we let it down. I find today's theories more nihilist, colder, there's vacuum everywhere, we've reached the end of the beginning !

we can't be right, we can be only wrong

I will wait till they find something right then.