The document discusses the chemical properties of alkanes and alkenes. It explains that alkanes contain carbon and hydrogen and are saturated hydrocarbons that are very stable due to strong C-H bonds. Alkanes undergo combustion and cracking reactions. Alkenes contain carbon-carbon double bonds, which make them more reactive than alkanes and allow them to undergo addition reactions with electrophiles such as halogens. The most important reaction of alkenes is polymerization, where alkene monomers combine to form large macromolecules or polymers. Common polymers include polyethylene, polypropylene, PVC, and PTFE.

1. Chemical properties of the alkanes
Explain why the old, non-systematic name for the alkanes was the paraffins:
Free radicals
Almost all alkane reactions involve the formation of
free radicals what are they:
Combustion
• When alkanes are heated in a plentiful supply of air, combustion occurs
• Alkanes are energetically unstable with respect to water and carbon dioxide
• They only burn when they are in the gaseous state
Explain what happens when a candle burns:
Sketch and energy profile for the combustion of propane:
Enthalpy
Cracking
• Cracking happens when alkanes are heated in the absence of air
• The products of the cracking of long-chain hydrocarbons are shorter chain molecules
• Ethane is cracked industrially to produce ethene
What are the conditions for catalytic cracking and what are the benefits of using a catalyst?

2. Write an equation for the cracking of dodecane to form one mole of ethene and an alkane product:
Breaking bonds
Homolytic fission
• Homolytic fission involves the equal sharing out of electrons in a
bond
• Each atom receives one electron from the bond when it splits
• This leaves the atoms with one unpaired electron
• The atoms are uncharged
• These ‘free radicals’ are very reactive
Why are free radicals so reactive?
In what type of situation is homolytic fission most likely to occur?
Draw a dot-cross and a curly arrow diagram for homolytic fission of chlorine (NB the curly arrow is
wrong in your textbook):
Heterolytic fission
• Heterolytic fission involves the unequal sharing of the electrons in a bond
• Both electrons go to one atom
• This results in the formation of two charged particles
In what type of situation is heterolytic fission usually seen?
Draw dot-cross and curly arrow diagrams for heterolytic fission:

3. Reactions with chlorine
• Alkanes only react with chlorine when a mixture of the two is exposed to sunlight or
ultraviolet light
• The light provides the energy required to break the very strong bonds
• This is an example of a substitution reaction
• There are three steps to the chain-reaction:
Initiation:
The Cl-Cl bond is easier to break than C-H
Propagation:
There are several possible propagation steps
Termination:
There are also several possible termination steps
Explain the difference in products produced when: methane reacts with a limited supply of chlorine
and with a plentiful supply of chlorine:

4. Chemical and physical properties of alkanes
Chemical properties
• Alkanes contain atoms of 2 elements: ____________ and __________
• Alkanes are _____________ hydrocarbons
• This means that they contain no carbon-carbon ___________
bonds
• Alkanes are very _________________ because they contain very
__________ bonds
• They do burn, and in sufficient oxygen produce _________ and __________ ___________.
Physical properties
• Alkanes are ________________ in water
• In straight-chain alkanes boiling temperature _______________ with chain length; however, this
trend is not followed by branched structural ________________.
Activity
Number these alkanes in order of increasing boiling point:
Propane Methane Octane Dotriacontane Heptane
1

5. Activity
Label the following pairs of structural isomers with highest boiling point (H) and lowest boiling point
(L):
Butane 2-methylpropane
Hexane 2,2-dimethylbutane
2,2,4-trimethylpentane Octane
Activity
Briefly explain the choices you have made in the above activities:
Structural Isomerism
“ Isomers are compounds with the same molecular formula but
different structural formula ”
Structural isomers have the same molecular _____________ but different
molecular ______________. This means that they have the same number of
_________ of the same ___________, but that these atoms are arranged
differently.
Exercise:
Determine displayed, skeletal, structural, molecular and empirical
formulae for all structural isomers of the 1st five compounds in the
alkane homologous series (methane-pentane), you can use the Molymod kits to help
you do this.

6. The alkenes
Comparison of bonding in ethane and ethene
Ethane
• The carbon-carbon single bond (σ bond) runs through the central axis of the molecule
• The two ends of the ethane molecule are free to rotate relative to each other
Ethene
• The ethene molecule is flat
• Ethene contains a carbon-carbon σ bond and a carbon-carbon double bond (π bond)
• The π bond lies above and below the central axis
• The π bond prevents rotation around the central axis
The carbon-carbon π bond is less than twice as strong as the carbon-carbon π bond, why?

7. What is and electrophile and why do alkanes readily react with them?
Naming alkenes
• We use the IUPAC naming system to name alkenes
• The suffix used is –ene
• We must use a number to indicate the position of the double
bond
Complete the table of alkenes:
ethene
but-1-ene but-2-ene
2-methylpent-2-ene

8. 2,4-dimethylhex-2-ene
Alkenes – Chemical reactions
Introduction
• Alkenes are far more reactive than alkanes
• They readily react with electrophiles
• They undergo addition reactions
• Addition reactions involve heterolytic fission of the
double bond
Electrophiles
• Species containing and atom with a whole or partial
________________ charge
• They are attracted to areas of high _____________
density
• They form a ______________ bond using a pair of
electrons from the π bond
• The most common electrophile is ________________
Addition reactions
1. Reaction with hydrogen
• Alkenes do not react with hydrogen under normal conditions…
Conditions:
2. Reaction with acidified potassium manganate(VII)
• This reaction involves addition across the double bond and oxidation
• The products are alkane diols
• Can be used as a test for _______________ as alkanes do not react

9. Conditions:
Observations:
3. Reactions with halogens
• Alkenes react halogens to form halogenoalkanes
• Reactions happen at room temperature and unlike the reaction of alkanes with halogens do
not involve ______ _____________
• Reactions become __________ vigorous down the halogen group (F > Cl > Br > I)
4. Reaction with bromine water
• Bromine water is an _______________ solution of bromine
• Addition takes place across the double bond and the bromine water becomes
_______________
• There are two different products _____________________ and _____________________
• 2-bromoethanol is formed because _____ ions from water also take part in the reaction

10. 5. Reactions with hydrogen halides
• Hydrogen halides are compounds containing ________________ and a halogen
e.g.
• Hydrogen halides react with alkenes readily at room temperature
• In the reactions hydrogen halides with higher alkenes (n > 2) there are two possible products
• Both possible products are formed but one is favoured, in this case ___________________
• The major product can be predicted using Markovnikov’s rule
Markovnikov’s rule:
“When HX adds across an asymmetric double bond, the major
product is the molecule in which hydrogen adds to the carbon
atom in the double bond with the greater number of
hydrogen atoms already attached to it”
Reaction mechanisms – “Curly Arrows”
Key words
• Electrophile –
• Nucleophile –

11. • Carbocation –
• Curly arrow –
Reaction mechanisms
• Mechanisms are diagrams that represent how organic chemistry reactions happen in terms of
the movement of electrons
• A single-headed curly arrow shows…
• A double-headed curly arrow shows…
Mechanism for the reaction of ethene with hydrogen bromide
Mechanism for the reaction of propene with hydrogen bromide
Remember Markovnikov? There are two possible products:
1.
2.
Both mechanisms involve carbocations (careful there’s a mistake in your book!):

12. • The carbocation in reaction ____ is more stable
• This is because the __________ groups donate electrons to stabilise the positive charge
• As a result the major product is ___________________
Mechanism for the addition of bromine to ethene
• The bromine-bromine bond is partially polarised by the electron rich ___ bond
• The first stage of the reaction is ________________ attack
• This is followed by _______________ attack on the carbocation by Br-
Polymerisation – The most important reaction of the alkenes
Key words
Polymer –
Monomer –
Synthesis of polymers
• Polymers are widely made in addition reactions

13. • Addition occurs across a double or triple bond
Common polymers
1. Poly(ethene) (polythene)
• Formed from the polymerisation of ____________________
• Comes in 2 forms __________ or ____________
• Conditions of polymerisation reaction determine which form is produced:
1.1 Low- density polythene (LDPE)
Properties Conditions of Diagram of structure
polymerisation reaction
Uses
1.2 High- density polythene (HDPE)
Properties Conditions of Diagram of structure
polymerisation reaction
Uses
2. Poly(propene)
Properties Conditions of Monomer
polymerisation reaction
Polymer

14. 3. Poly(chloroethene) (PVC)
Properties Conditions of Monomer
polymerisation reaction
Polymer
4. Poly(tetrafluoroethene) (PTFE / “Teflon”)
Properties Monomer
Polymer
Properties of polymers
• The physical (e.g. _________________ , __________________ and ________________)
and chemical properties of polymers depend on their molecular structure:
1. Average length of polymer chain
• Tensile strength
• Melting temperature
2. Branching of the chain
• Tensile strength
• Melting temperature
• Density
3. Intermolecular forces between chains
• Tensile strength
• Melting temperature
4. Cross- linking between chains
• Rigidity

15. • Hardness
• Flexibility
• Melting temperature