-alkenes have C=C double bonds. (they are hydrocarbons)
-they are known as unsaturated as the double bond could be opened up to allow the two carbon atoms to bond with other atoms.
-the first three alkenes are ethene (two carbon atoms)porpane (threeC's) and butene (four C's)
- alkenes have a formula. CnH2n - this means they have twice as many hydrogen as carbon atoms
- carbon atoms always make four bonds however hydrogen only one. .