1. Hydrocarbons Straight and Branched All Single Bonds Aliphatic Alkanes
Cyclic
Alkenes
At least one Double Bond
Alkynes
At least one Triple Bond
Aromatics
Benzene ring
Delocalised Pi Bonds

2. Sources of Hydrocarbons

3. Structure of Aliphatic Hydrocarbons

4. PETROCHEMICALS
In the past, the most important organic chemicals were derived from coal.
Nowadays, natural gas and crude petroleum provide an alternative source.
The composition of crude petroleum varies according to its source. It is a dark coloured, viscous liquid
It consists mostly of alkanes with up to 40 carbon atoms, plus water, sulphur and sand
It can be split up into fractions by fractional distillation. Distillation separates the compounds according to their boiling point

5. Crude Oil

6. Hydrocarbons
Compounds which contain only carbon and hydrogen bonded together covalently
Sources
Coal
Natural Gas
Petroleum [Crude Oil]

7. General members of a homologous series
ALKANES
General members of a homologous series
general formula is CnH2n for non-cyclic alkanes
saturated hydrocarbons - all carbon-carbon bonding is single
bonds are spaced tetrahedrally about carbon atoms.
Have the same functional group
Have similar chemical properties
Show gradation in physical properties

8. Alkanes Alkanes CnH2n+2 Methane CH4 GAS Ethane C2H6 GAS
Propane C3H GAS
Butane C4H GAS
Pentane C5H LIQUID
Hexane C6H LIQUID

9. THE STRUCTURE OF ALKANES
In ALKANES, the four orbitals of carbon repel each other into a TETRAHEDRAL arrangement with bond angles of 109.5º.
Each orbital in carbon overlaps with the 1s orbital of a hydrogen atom to form a C-H bond.
109.5º

10. Methane
Methane is produced from the remains of marine animals and plants that sank to the bottom of ancient seas and lakes.
Methane is produced in the formation of coal.
Methane is produced in an uncontrolled way in slurry pits and refuse dumps.
Methane also is produced in large quantities in the digestive tracts of animals such as cattle.

11. Hazards of Methane
In coalmines methane can produce an explosive mixture with air.
Methane is produced in uncontrolled amounts in slurry pits and refuse dumps and if a source of ignition is provided then fires or explosions can occur.
Methane production in slurry pits also causes deaths by suffocation.
Contributes to Greenhouse Effect

12. Greenhouse Effect Result Temperature Rises
Long and Short Wave from Sun
Soil and Plants
Long
Short
Long Wave reflected by Glass [or atmosphere]
Short Wave enters
Plants and Soil absorb Short Wave
Plants and Soil then emit Long Wave
Long Wave Reflected by Glass so Trapped
Result Temperature Rises

13. Enhanced Greenhouse Effect
Long and Short Wave from Sun
Soil and Plants
Long
Short
Greenhouse Gases
Long Wave reflected by greenhouses gases
Short Wave enters
Plants and Soil absorb Short Wave
Plants and Soil then emit Long Wave
Long Wave Reflected by greenhouse gases so Trapped
Result Temperature Rises

14. Greenhouse Gases
Water Vapour
Methane
Nitrous Oxides
CFCs
Carbon Dioxide
Methane comes from cattle, landfills and Paddy Fields
Nitrous Oxides from exhausts
CFCs from aerosols, refrigeration unit, etc.
High levels of CO2 comes from burning fossil fuels
(home heating, transport)

15. Greenhouse Effect Greenhouse gases Cause Global Warming
Climate Changing
Melting Polar Caps
More violent weather
Growth of deserts
Rising sea levels
Flooding of low lying cities
Spread of tropical pests and diseases such as malaria

16. PHYSICAL PROPERTIES OF ALKANES
Boiling point increases as they get more carbon atoms in their formula
more atoms = greater induced dipole-dipole interactions
greater intermolecular force = more energy to separate the molecules
greater energy required = higher boiling point
CH4 (-161°C) C2H6 (-88°C) C3H8 (-42°C) C4H10 (-0.5°C)
difference gets less - mass increases by a smaller percentage
Straight chains molecules have greater interaction than branched
“The greater the branching, the lower the boiling point”
STRUCTURAL ISOMERS OF C5H12
HIGHEST BOILING POINT LOWEST BOILING POINT

17. PHYSICAL PROPERTIES OF ALKANES

18. PHYSICAL PROPERTIES OF ALKANES
Melting point general increase with molecular mass
the trend is not as regular as that for boiling point.
Solubility alkanes are non-polar so are immiscible with water
they are soluble in most organic solvents.

19. CHEMICAL PROPERTIES OF ALKANES
Introduction - fairly unreactive; (old family name, paraffin, meant little reactivity)
- have relatively strong, almost NON-POLAR, SINGLE covalent bonds
- they have no real sites that will encourage substances to attack them
Combustion - make useful fuels - especially the lower members of the series
- react with oxygen in an exothermic reaction
complete CH4(g) O2(g) ——> CO2(g) H2O(l)
combustion
incomplete CH4(g) ½O2(g) ——> CO(g) H2O(l)
the greater the number of carbon atoms, the more energy produced
BUT the greater the amount of oxygen needed for complete combustion.
Handy tip When balancing equations involving complete combustion, remember...
every carbon in the original hydrocarbon gives one carbon dioxide and
every two hydrogen atoms gives a water molecule.
Put the numbers into the equation, count up the O’s and H’s on the RHS
of the equation then balance the oxygen molecules on the LHS.

20. Alkyl Groups
Methyl CH3
Ethyl C2H5
Propyl C3H7
Butyl C4H9
Pentyl C5H11

21. STRUCTURAL ISOMERS OF C5H12
Isomerism the first example of structural isomerism occurs with C4H10
BUTANE METHYLPROPANE
Structural isomers have the SAME MOLECULAR FORMULA BUT
DIFFERENT STRUCTURAL FORMULA
They possess different physical properties such as boiling point,
melting point and density
STRUCTURAL ISOMERS OF C5H12
PENTANE
2-METHYL BUTANE
2,2 DIMETHYL PROPANE

22. Alkenes
Alkenes are a homologous series of hydrocarbons with the general formula CnH2n
They are named systematically, with a prefix indicating the number of carbon atoms per molecule, and the ending “ene”

23. Alkenes
Ethene C2H4
Propene C3H6
But-1-ene C4H8
But-2-ene C4H8

24. Ethene C2H4

25. Propene C3H6

26. But-1-ene C4H8

27. But-2-ene C4H8

28. 2,methylpropene C4H8
CH3
CH C CH2

29. Physical properties of alkenes
Physical state: Gases
Insoluble in water
Soluble in non-polar solvents such as cyclohexane

30. Alkynes
Alkynes are a homologous series of hydrocarbons with the general formula CnH2n-2
Ethyne (C2H2) is the first member of the series

31. Physical properties of ethyne
Physical state: Gas
Insoluble in water
Soluble in non-polar solvents such as cyclohexane

32. Other Alkanes
Hexane
Heptane
Octane
Cyclohexane
2,2,4 trimethylpentane