1. Alkanes are hydrocarbons in which all carbon atoms are bonded by single covalent bonds

2. Alkanes are said to be saturated because all the bonds are single bonds.

3. The alkanes are named according to the number of carbon atoms (methane, ethane, propane, butane, pentane etc.)

4. Alkanes do not turn bromine water colourless

AlkanesAlkanesAlkanesAlkanes

Alkanes

AlkanesAlkanesAlkanesAlkanes

Alkanes

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C

H

H

H H methane, CH4

C

H

H

H C

H

H

H ethane, C2H6

C

H

H

H C

H

H

C

H

H

H propane, C3H8

Alkanes

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butane, C4H10

C

H

H

H C

H

H

C

H

H

C

H

H

H

pentane, C5H12

C

H

H

H C

H

H

C

H

H

C

H

H

C

H

H

H

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C

H

H

H C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

H

hexane, C6H14

and so on…………

Notice the carbon chain

is not really straight

1. Hydrocarbons with long chains have limited use due to their lack of flammability

2. Large hydrocarbons can be broken down (cracked) into smaller, more useful substances

3. This process uses heat and a catalyst4. It is a type of thermal decomposition

reaction

CrackingCrackingCrackingCracking

Cracking

CrackingCrackingCrackingCracking

Cracking

CrackingCrackingCrackingCracking

Cracking

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Catalytic Cracking• In the catalytic cracker long chain molecules are split

apart or ‘cracked’. An example of such a reaction is:

C8H18 C6H14 + C2H4

C CH

H

H

H+

ethene

C CH

H

H

H H

C C C C C C

H

H

H

H

H

H

H

H

H

H

H

H

H

Octane

C CH

H

H

H H

C C C C

H

H

H

H

H

H

H

H

H

hexane

Etheneis usedto makeplastics

Heat pressure

catalyst

Used as a fuel

1. Alkenes are hydrocarbons that contain at least one carbon-carbon double bond

2. Alkenes are said to be unsaturated because of that double bond – written C=C.

3. Alkenes can be identified using bromine water. The yellow-brown bromine water goes colourless.

AlkenesAlkenesAlkenesAlkenes

Alkenes

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Saturated or Unsaturated?• Saturated means “full up”.

• They have a double bond that could instead become two single bonds. This means that other atoms can be added. It is not “full up”.

• Alkenes are unsaturatedunsaturated.

• Every carbon atom has already used all four of it’s bonds to join to four other atoms. No other atoms can be added.

• Alkanes are saturatedsaturated.

AlkenesAlkenesAlkenesAlkenes

Alkenes

AlkenesAlkenesAlkenesAlkenes

Alkenes

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• Copy the Table and complete the empty boxes.

Number of

carbons

Name Alkane or alkene

Formula

5 pentene

8 octane

4 butene

10 decane

alkene C5H10

alkane C8H18

alkene C4H8

alkane C10H22

Activity

1. Alkenes are reactive and are called monomers

2. Monomers (e.g. ethene) can react together to form polymers (e.g. poly(ethene))

3. This process is called polymerisation4. Addition polymerisation has taken

place if no other products are made5. Plastics are polymers

PolymersPolymersPolymersPolymers

Polymers

PolymerisationPolymerisationPolymerisationPolymerisation

Polymerisation

Monomers and PolymersMonomers and Polymers

Ethene

Here’s ethene again. Ethene is called a MONOMER because it is just one small molecule. We can use ethene to make plastics…

Step 1: Break the double bond

Step 2: Add the molecules together:

This molecule is called POLYETHENE, and the process that made it is called POLYMERISATION

Another way of drawing it…Another way of drawing it…Instead of circles, let’s use letters…

Ethene

C C

HH

HH

C C

HH

HH

Ethene

H

C C

H

HH

H

C C

H

HH

Poly(e)thene

General formula for addition polymerisation: HIGHER

C Cn C C

n

e.g. C Cn

H CH3

HH

C Cn

H CH3

HH

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Poly(e)thene• One important reaction of alkenes involves the joining

together of alkene molecules.

C CH

H

H

H HH

C CH

H H

H H

C C

H H

HH

C C

H H

HH

C C

H H

HH

C C

H HAndlotsmore..

HIGHER: This is called addition polymerisationaddition polymerisation and is written as:

Pressure

high temperaturecatalyst

C CH

H

H

HC C

HH

H H

n

n

ethene

poly(e)thene

1 2 3 4 5 thousands

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PVC• Vinyl chloride is another alkene that is made into an

important plastic used to make e.g synthetic leather, wellington boots,guttering.

n

tetrafluoroethene Poly(tetrafluoroethane)or PTFE

n

C C

F F

F FC C

F

F

F

F

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PTFE• Tetrafluoroethane is another alkene that is made into an

important plastic used to coat non-stick pans: polytetrafluoroethane or PTFE.

n

tetrafluoroethene Poly(tetrafluoroethane)or PTFE

n

C C

F F

F FC C

F

F

F

F

© Boardworks Ltd 2003

Some uses of plastics

Poly(e)thene

Shopping bags

Bottles

Buckets

Washing up bowls

Polypropene

Milk crates

Rope

Carpet fibres

Polystyrene

packing

insulation

Ball pens

1. Poly(ethene) is used for making plastic bags and bottles

2. Poly(propene) is used for making crates and ropes

3. Most plastics are not biodegradable – they cannot be broken down by microorganisms. They can lead to problems with waste disposal

Uses of PlasticsUses of PlasticsUses of PlasticsUses of Plastics

Uses of Plastics

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1 2

3

4 5 6

7

8

9

Across Down

 3) separate substances with different boiling points

1) Contain a double bond

7) saturated hydrocarbon

2) a series of molecules differing by a CH2

8) joining of many small molecules

4) breaking up a large molecules

9) full up: unable to add more atoms

5) the different substances collected from distillation

6) used to test for unsaturated molecules.

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Which of these is an alkane?

A. C6H14

B. C4H8

C. C12H24

D. C102H204

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Which of these is a true statement aboutalkenes?

A. They turn bromine water from colourless to red

B. They contain a double bond

C. The smallest alkene has 1 carbon atom

D. They have names that end in “ane.”

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Which of these is a true statement about cracking?

A. it is the separation of molecules into fractions of different sizes.

B. it is carried out at low temperatures

C. it uses a catalyst.

D. It produces polymers

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Which of these is a true statement about polymerisation?

A.it is the joining together of many small molecules.

B. it is the thermal decomposition of plastics

C.it is carried out using saturated molecules

D.it is a multiplication reaction

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Which of these is an addition polymer?

A. styrene

B. ethene

C. p.v.c.

D. propane

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How might you test to see if polystyrene stillcontained some unsaturated monomer (styrene)?

A. Crush it up and burn it.

B. Crush it up and add it to bromine water

C. Crush it up and dissolve it in petrol

D. Crush it up and add hydrochloric acid