He (helium)

Physical properties:Helium is a colourless and odourless gas.After hydrogen, it has the smallest density of all gases.Its fusion point is the lowest that can be observed (-271,4 ^oC).Chemical properties:Helium is chemically inert. It does not form any compounds.Natural state:The most frequent atoms in the universe are hydrogen atoms. Helium follows with 7,19%. On earth, helium is very rare (0,0000004% of the earth's crust). The sun produces helium from hydrogen.Applications:Owing to its weak density, helium is used in airships.Because of its weak solubility in blood and fat tissue, helium remplaces favorably nitrogen in deep-sea diving.

The noble gases