Organic molecules composed exclusively from the atoms of carbon and hydrogen. A huge variety of possible compositions of these atoms exist. The whole organic chemistry including the chemistry of all living species is based on these molecules.
Just the simplest group, the group of the alkenes which is characterized by a linear chain of single-electron-connected Carbon atoms ranges from the smallest molecule methan with just one carbon atom up to linear polymers with more than 100.000 carbon atoms. The group includes the fossile oil fractions methane, ethane, butane, propane up to their linear long chain polymers which form the group of polyethylenes
Additional important groups of hydrocarbons are the alkines, cycloalkanes and aromates. Aromates are based on a hexagone ring of carbon atoms.