elementsOxygen (Latin: oxygenium, symbol O, atomic number 8) is a non- metal that belongs to the oxygen group in the Periodic Table. Oxygen comes as a single agent, especially as dioxygen (O2) in the atmosphere. In composite form it is widespread because all the water and all silicates of the earth's crust contain oxygen. By weight, oxygen is the most abundant element in the human body, about 65%, especially in the form of water.

Nitrogen (symbol N, atomic number 7) is a non- metal from the group of nitrogen. Loose atoms of these are highly reactive and bind directly to other nitrogen atoms. Then is usually formed dinitrogen (N2 or molecular nitrogen), the usual appearance of nitrogen. N2 at room temperature is in gaseous form.

Hydrogen (symbol H (Latin: Hydrogenium), atomic number 1) normally occurs not in isolated form, but is due to the high reactivity connected. It forms a diatomic molecule: dihydrogen, usually just called hydrogen. Hydrogen is the most abundant element in the universe. The normal isotope of hydrogen "protium" consists of only one proton and one electron, and thus contains no neutrons. Hydrogen is the only element that exists without neutrons.

Carbon (symbol C, atomic number 6) exists in different forms (charcoal, diamonds...) and is in hydrocarbons (fossil fuel), carbohydrates (ethanol, sugars, starch...). All organic compounds contain carbon. (Only CO2 and carbonates are still seen as inorganics.) Carbon compounds form the basis of all life on Earth.

Sucrose, sugar: C12H22O11
C6H12O6 burns > 6CO2 (g) + H2O (g) (reverse= photosynthesis)
Gas = methane CH4 burns :CO2 and H2O. Ethane:
Carbohydrates: ((CH2O)) n
Alcohol: C2H5OH