Question

What are the most abundant compounds in the universe and on earth?

In the [100 Most Important Chemical Compounds](http://books.google.com/books?id=MwpQWcIKMzAC&printsec=frontcover) there is a listing of 100, but not in order of abundancy, and I really need only 1/4 of that amount at most.

Answer 1

In the universe, assuming you are restricting yourself to neutral compounds, you probably have H2, H2O, and CH4. The universe is about 3/4 hydrogen, which explains H2 and why everything else has as much H as possible. Oxygen and carbon are particularly stable nuclei, and readily formed by fusion in large stars, so that's why there's a lot, relatively speaking, of oxygen and carbon in the universe.

On the surface of the Earth, there is, at present, quite a lot of free oxygen (O2), generated by photosynthesis of green plants. This is quite different from the universe as a whole. (Chemists say the surface of the Earth is a strongly oxidizing environment, while the universe as a while is strongly reducing.) There is very little hydrogen, because the Earth's gravity is not sufficient to hold H2 in the atmosphere. So what we have is lots of H2O (in the oceans), plus (in the atmosphere) lots of O2 and N2. There is a fair amount of CO2 in the oceans, very little in the atmosphere. In the rocks of the crust, you have enormous amounts of silica (SiO2), which comes in many different types.

Answer 2

I found some tables by googling "most abundant compounds earth's crust" and so forth.

Answer 3

Thank you, that was quite informative. Regarding the compounds that reside in the earth's crust (I've googled that before, too) - could you please tell me what is the ratio of all those combined of the other compounds on earth?