Chapter 8

Compounds of Carbon

Why is Carbon important?

They make up over 90% of all chemical compounds, is the backbone of all living things.

Make element in “organic substances”.

Proteins, carbohydrates and fats all

contain carbon.

Natural Gas-formed by the natural degradation of organic matter. Found with

deposits of petroleum.

HydrocarbonsCompounds of Carbon and Hydrogen.

Methane (CH4) is the simplest hydrocarbon and belongs to the alkane group.

Alkanes end with suffix –ane.

Carbon-Carbon single bonds.

Other alkanesGeneral formula: CnH2n+2

n= number of carbon atoms

As the number of C atoms increases the structure has an additional –CH2 group. This is known as homologous series.

Structural formulas and condensed formulas

• Condensed formula of alkanes

• E.g. Butane C4H10

Structural formulas

Shows how the elements are arranged relative to one another (straight chain representation). E.g. Butane

• Branched chain- when alkyl groups branched off the main parent chain.

• Alkyl groups – CnH2n+1

Alkyl groups end with

suffix -yl

Name Formula

Methyl -CH3

Ethyl -CH2CH3

Propyl -CH2CH2CH3

Butyl -CH2CH2CH2CH3

Pentyl -CH2CH2CH2CH2CH

3

Isomers- have the same molecular formula but different structural formula

• The general formula of a 4 carbon alkane is C4H10

• C4H10 has 2 isomers : Butane and 2-methyl propane

• Note: the importance of numbering carbons in branched chains.

Alkanes summary1. End with suffix –ane.2. Single bonds between C-C atoms, hence saturated hydrocarbons.3. As the number of carbon atoms increase the hydrocarbons change from gases to liquids to solids.

Alkenes- have a double bond between C=C (note there’s one double bond only, the rest are

single bonds)

End with suffix –ene.

General formula: CnH2n

Ethene to Decene

Formula NameC2H4 Ethene

C3H6 Propene

C4H8 Butene

C5H10 Pentene

Alkenes are considered unsaturated hydrocarbons due to the presence of a double bond.

• Under the right conditions alkenes can react with hydrogen to form alkanes.

Alkynes- have a triple bond between carbon-carbon bonds (one triple bond only) so are

unsaturated

Alkynes have a General formula: CnH2n-2

Important- the double or triple bond should be on the 1st carbon

Rules for naming branched hydrocarbons Identify the parent chain (the longest continuous carbon

chain)

Identify the branch or substituent (usually an alkyl group)

Number the carbon atoms in such a way (from the end that gives the branched group the lowest number possible).

Refer to pages 142-143 of your Chemistry textbook.

I will do a few examples on the board before you start the worksheets!!!

Quick quiz!!! Which hydrocarbon has a double bond?

What does saturation mean?

What is the general formula of an alkyne?

What are isomers?

What is a parent chain?

Are alkenes saturated or unsaturated?

What happens to the states of alkanes as the number of carbon atoms increase?

What number is assigned to the carbon that has a side or branched chain?

Answers

Alkenes

Single bond between carbon atoms

CnH2n-2

Same general formula but different structural formula

Longest straight carbon chain

Unsaturated due to double bond between Carbon to Carbon

Changes from gases to liquids and then to solids

Lowest number possible

Properties of alkanes and alkenes

• Physical properties (both similar for alkanes and alkenes)

Smaller molecules are more volatile than larger ones (less energy is needed to overcome forces between molecules).

Smaller molecules are less viscous (thickness of fluid) so flow more freely.

Petrol is less viscous than oil and more volatile so burns more readily.

Boiling temperature increases as the number of carbon atoms increase (However, alkenes are slightly lower than alkanes)

Forces between Hydrocarbon molecules

• Non-polar because of the similar electronegativities between C and H.

• Dispersion forces exist- this force increases as size of molecule increases.

• More energy is required to overcome the intermolecular dispersion forces of larger molecules hence higher boiling temperatures

• Also stronger intermolecular dispersion forces between larger molecules means it is harder for the liquid to evaporate (less volatile)

• Larger molecules are more viscous due to longer chain hydrocarbons becoming “tangled together”.

Chemical properties of alkanes

• 1. Combustion

• Alkanes burn in oxygen to form carbon dioxide and water.

• Methane + Oxygen → Carbon dioxide + Water

• Balanced chemical equation (You should be able to balance equations using coefficients)

• CH4 + 2O2 → CO2 + 2H2O

Chemical Properties of alkenes• Like alkanes, alkenes also burn in oxygen to produce carbon

dioxide, water + heat. The presence of a double bond allows alkenes to react more readily with others.

• 1. Addition Reactions with Bromine

The double bond breaks forming: Red brown colour of bromine

d disappears as it reacts with

ethene. This is the test for

unsaturation.

Reactions with Bromine

• 2. Reactions with Hydrogen

In the presence of a catalyst (Platinum-Pt) ethene reacts with hydrogen to form ethane.

This is an addition reaction where the double bond breaks to allow hydrogen to bond with carbon.

3. Reaction with steam

• Ethanol is now being made by adding steam (H2O) to ethene. Phosphoric acid is used as a catalyst. This is also an addition reaction with steam.

• Ethene + Steam → Ethanol

4. Formation of polyethylene

• Another name used for ethene is ethylene. Polyethylene or polyethene means “many ethylene” or “many ethene”.

• Polyethylene is a polymer that is a large molecule made by many small units of ethene (monomer). This type of reaction is also called an addition polymerisation reaction.

• n in this reaction is very large (10,000 or more)