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Elements most common in the Earth's crust are: Oxygen, Silicon, Aluminium, Sodium

Elements most commonly found in living organisms: C, H, O, N.

The biological importance of C,H,O,N is is large due to having valencies of 1,2,3,4

ability to form more stable covalent bonds than any other element with these valencies.

IMPORTANCE OF CARBON

"Organic" <living> was used bc it was thought that only living things could make organic compounds.

Wohler dispelled the myth in 1828 when he synthesised urea from inorganic starting materials. It is proven that no special life force is needed to make the biochemicals of life.

Carbon forms strong covalent bonds, sharing its e- w other elements and forms a tetrahedral arrangement.

C either forms chains or rings that are the skeletons of organic molecules and life.

They are very stable because cov. bond linking carbon atoms together are strong

IMPORTANT CHEMICAL PROPERTIES OF CARBON

. Relatively small atom w low mass

. forms 4 strong, stable cov. bonds

. forms C-C bonds, building up large C skeletons w. ring and/or chain structures

. has the ability to form multiple cov. bonds w other C atoms. O