Alkenes
It is a hydrocarbon in which carbon atoms are connected by double bonds .
Example: Ethene
 Formula of Ethene is C _{ 2 } H _{ 4 } .
 There is 1 double bond between 2 Carbon atoms.
 Since Carbon has 4 valence electrons and only 2 of them are shared by other carbon atom, the remaining 2 electrons are shared by 2 hydrogen atoms each.
Hence there are a total of 2 carbon atoms and 4 hydrogen atoms .
General formula for Alkenes
It Is C _{ n } H _{ 2n }
 Where n is the number of carbon atoms.
Number of Carbon Atoms (n) 
n=2 
n=3 
n=4 
Name of Alkene 
Ethene 
Propene 
Butene 
Structure 



Example: Formula for Butene
 In Propene, there are only 4 carbon atoms.
 So the formula is,
C _{ n } H _{ 2n }
 Putting n=4
C _{ 4 } H _{ 2*4 }
C _{ 4 } H _{ 8 }
Name of Alkene 
Formula Derivation C _{ n } H _{ 2n } 
Number of Carbon Atoms (n) 
Ethene 
C _{ 2 } H _{ 4 } 
n=2 
Propene 
C _{ 3 } H _{ 6 } 
n=3 
Butene 
C _{ 4 } H _{ 8 } 
n=4 
Pentene 
C _{ 5 } H _{ 10 } 
n=5 
Hexene 
C _{ 6 } H _{ 12 } 
n=6 
Heptene 
C _{ 7 } H _{ 14 } 
n=7 
Octene 
C _{ 8 } H _{ 16 } 
n=8 
Nonene 
C _{ 9 } H _{ 18 } 
n=9 
Decene 
C _{ 10 } H _{ 20 } 
n=10 