[iamcuriousagain]

Hi All,

how did we figured out all the elements that we have on periodic table ?

For example we know a water molecule contains 2 parts of hydrogen and one part of oxygen,
but even before we claim this, don't we have to establish a fact that hydrogen and oxygen exists independently and
then figure out that they exists in water as H₂O ?

[Hunter2]

Hundreds years ago the allchemist and later the chemists worked it out. By watching, doing experiments and found at the end some  material, what cannot devided by chemical reaction anymore.(in greece language they called it atomous, where the word atom comes from).
Later in the last century in the 30ties, it was found also atoms can be more devided in smaller atoms and particles, with all the results of nuclear power, atomic bomb, etc.

[mjc123]

There was a recent BBC TV series on this subject by Professor Jim Al-Khalili called "Chemistry: A Volatile History". Apparently it aired in the USA under the title "Unlocking the Universe". It is not currently available on BBC iplayer, but there is a good short summary on Wikipedia: http://en.wikipedia.org/wiki/Chemistry:_A_Volatile_History