[adit]

Even Galileo and Isaac Newton did not know the following fact.

There are certain number of elements (now it is known to be 118).  These elements unite in various ways to form billions of compounds.  The materials in the world are made of either the elements or the compounds derived from these elements.

Who discovered the above fact.  I am NOT asking who discovered each and every element (which has been described in the following article)
http://education.jlab.org/qa/discover_ele.html

I am asking:
1) Who discovered the GENERAL FACT that materials in the world are made of certain number of elements and compounds derived from these elements.

2) When was it discovered?

[Borek]

In a way there was no such single discovery.

Initially it wasn't even clear what an element is. By definition, element was a "simple" substance - one that can not decomposed further. However, some substances were treated as elements, as early chemists/alchemists were not able to decompose them into simpler substances. Some of these substances were later found to be compounds.

Number of elements was for long time unknown and slowly growing, around the time Mendeleev published his periodic table it became obvious that elements properties follow some pattern, but even at the time it wasn't clear how many are there. However, PT put a limit on the number of simple substances - assuming they had to follow the pattern, there was only a limited number of places in PT. This approach was once proven to be partially false, with the discovery of noble gases.

[Arkcon]

Perhaps you're interested in the work of John Dalton, he developed an atomic theory that he used a symbolic shorthand for:

http://en.wikipedia.org/wiki/John_Dalton#Five_main_points_of_Dalton.27s_atomic_theory

He was building on some theoretical proportions being worked on by Lavoisier -- until the blade dropped:

http://en.wikipedia.org/wiki/Antoine_Lavoisier#Pioneer_of_stoichiometry