1. Hydrocarbons

2. Hydrocarbons
Molecules which contain the elements HYDROGEN and CARBON ONLY
Obtained from crude oil by FRACTIONAL DISTILLATION:
Increasing molecular size Decreasing Flammability
Increasing boiling point
Increasing viscosity

3. Hydrocarbon Families Alkanes Cycloalkanes Alkenes
Hydrocarbons are divided up into families
A family of hydrocarbons which all fit the SAME GENERAL FORMULA and which all have SIMILAR CHEMICAL PROPERTIES is called a
HOMOLOGOUS SERIES
Alkanes
Cycloalkanes
Alkenes

4. Alkanes
All members are in STRAIGHT CHAINS and have only SINGLE carbon-to-carbon bonds
All members of the family have an individual name
1st part of name tells you how many carbon atoms are in the hydrocarbon:
Meth = But = Hept = 7
Eth = Pent = Oct = 8
Prop = Hex = 6
2nd part of name tells you which family the hydrocarbon belongs to:
-ANE = Alkanes

5. Mnemonic Number of Carbon atoms Prefix Memory Aid 1 Meth- Monsters 2
Eat 3
Prop-
People 4
But-
But 5
Pent- 6
Hex-
Hate 7
Hept-
Having 8
Oct-
October 9
Non-
November 10
Dec-
December

6. Methane Each carbon atom forms 4 bonds Each hydrogen atom forms 1 bond

7. Formulae CH4 C2H6 C3H8 CH4 CH3 CH3 CH3 CH2 CH3 Full structural
Shortened structural
Molecular

8. General Formula
CnH2n + 2
E.g. If there are 5 carbon atoms, the number of hydrogen atoms is 2 x = 12
Each family member differs by a CH2 unit:

9. Properties
This REGULAR INCREASE in a CH2 unit means that as you move through the family, there is a gradual change in PHYSICAL PROPERTIES
e.g. boiling point
The CHEMICAL PROPERTIES in each member of the family are all very SIMILAR
e.g. flammability

10. Titan: Saturn’s largest moon

11. CnH2n Cycloalkanes CH2 CH2 CH2 C3H6 CH2 CH2 CH2 CH2 C4H8
Are another HOMOLOGOUS SERIES of hydrocarbons
This time, each member forms a RING shape
CH2
CH CH2
C3H6
Cyclopropane
CH CH2
CH CH2
Cyclobutane
C4H8
CnH2n

12. H C Ethene CnH2n Alkenes Are another HOMOLOGOUS SERIES of hydrocarbons
Each member is in a straight chain
Each member contains a carbon-to-carbon DOUBLE BOND C H
Ethene
- The first member of this family
CnH2n

13. Members of the Alkene FamilyC H
Ethene
C2H4
CH2=CH2 C H
Propene
C3H6
CH3CH=CH2 C H
Butene
C4H8

14. Saturated vs Unsaturated
Alkanes, cycloalkanes
Only carbon-to-carbon SINGLE bonds
No other atoms will join on to the molecule C H
Unsaturated:
Alkenes
Contains at least one carbon-to-carbon DOUBLE bond
Other atoms can join on to the molecule

15. Addition Reactions
Hydrocarbons with a C=C can react with other atoms to let them ADD ON.
This is called an ADDITION REACTION 1 2
The new atoms join on to EITHER SIDE of the DOUBLE BOND

16. Test for Unsaturation
Bromine solution can be used to distinguish between alkanes and alkenes, or cycloalkanes and alkenes
Hydrocarbon
Test with bromine solution
Saturated / unsaturated
Alkane
Saturated
Stays brown / red
Cycloalkane
Saturated
Stays brown / red
Alkene
Unsaturated
Changes from brown / red to colourless
Br2 (aq)

17. Supply vs Demand
Less produced
Lots produced
High demand
Low demand

18. Cracking
Is used to make smaller, more useful molecules from larger molecules
Bond breaks
(random)
High temperature

19. Cracking in the Lab Can be done in the laboratory: Aluminium oxide
Cracked gas
Alkane

20. Isomers
Hydrocarbons with the SAME NUMBER of atoms but DIFFERENT structures are called ISOMERS
Isomers can be of hydrocarbons in the SAME FAMILY:
C4H10
Or in DIFFERENT FAMILIES: C H
C3H6