C/W Reactions of alkenes 21/1/20 With oxygen – combustion Less energy and Smokey flame due to incomplete C3H6+ 4 ½ O2 -> 3h20 + 3co2 Functional Group – are groups of one or more atoms or bonds (except double bond) of distinctive chemical properties. Homologous Series - family of hydrocarbons with similar chemical properties who share the same general formula. A displayed formula - shows all the bonds in the molecule as individual lines. 2A. General formula of Alkenes: Cn H2n 2B. Octane has 8 carbons, how many carbons does it have: C8 H19 3. Why are alkenes unsaturated? Because they have a double carbon bond. 4.