1. Unit 2 Summery Nature’s Chemistry
National 5 Supported Study

2. Mandatory Key Area Homologous series
The study of cycloalkanes and branched chain alkanes and alkenes (up to C8).
To include their physical, chemical properties, general formulae, systematic names, structural formulae, uses, reactions and isomers.
Reactions — combustion and addition.

3. Key Definitions
Homologous Series – family of compounds with same general formula and similar chemical properties
Isomers - Have the same molecular formula but a different structural formula.
Butene and cyclobutane are isomers

4. Family 1 : Alkanes Alkanes Are straight chained hydrocarbons
All end in –ane

5. Naming Alkanes (pg 9 DB) Methane - 1 carbon Ethane - 2 carbons
Propane - 3 carbons
Butane - 4 carbons
Pentane - 5 carbons
Hexane - 6 carbons
Heptane - 7 carbons
Octane - 8 carbons
All Alkanes end in –ane

6. Monkey's Eat Peanut Butter
Meth
Eth
Prop
But

7. General Formula

8. Shortened structural formula
Alkanes
No. carbon
Name
Shortened structural formula
Formula 1
Methane
CH4 2
Ethane
CH3-CH3
C2H6 3
Propane
CH3-CH2-CH3
C3H8 4
Butane
CH3-CH2-CH2-CH3
C4H10 5
Pentane
CH3-CH2-CH2-CH2 -CH3
C5H12 6
Hexane
CH3-CH2-CH2-CH2-CH2 -CH3
C6H14

9. Family 2: Alkenes Are straight chain hydrocarbons End in – ene
Contain a carbon to carbon DOUBLE bond
General Formula
CnH2n

10. Naming Alkenes Ethene - 2 carbons Propene - 3 carbons
Butene - 4 carbons
Pentene - 5 carbons
Hexene - 6 carbons
Heptene - 7 carbons
Octene - 8 carbons
All Alkenes end in –ene
Why does Methene not exist????

11. Shortened structural formula
Alkenes
No. carbon
Name
Shortened structural formula
Formula 2
Ethene
CH2=CH2
C2H4 3
Propene
CH2=CH-CH3
C3H6 4
Butene
CH2=CH-CH2-CH3
C4H8 5
Pentene
CH2=CH-CH2-CH2 -CH3
C5H10 6
Hexene
CH2=CH-CH2-CH2-CH2 -CH3
C6H12

12. Saturated Vs Unsaturated
Saturated = single carbon to carbon bonds only
Unsaturated = contains carbon to carbon double bonds.
Remember
Keep the S’s together (saturated/single)
Keep the U’s together (Unsaturated/Double)

13. Alkenes decolourises bromine water.
Bromine water is used to distinguish between saturated and unsaturated compounds.
Alkenes decolourises bromine water.

14. Family 3: Cycloalkanes Ring structure Saturated Cyclopropane first
Member of series
General Formula
CnH2n
(same as alkenes)

15. PRACTICE PRACTICE PRACTICE
Systematic Naming
Find the longest chain (numbering carbons helps)
Always give functional group lowest numbers
“,” between numbers and “–” between numbers and words
PRACTICE PRACTICE PRACTICE

16. Systematic Naming
Branched chain alkanes
Branched chain alkenes

17. Branched Chain Alkanes
Find the longest chain
Note – it might not always be the most obvious one, Could be going up and down a page, or have a bend it. You are looking for the longest path.

18. Don’t be tricked!!
Longest chain is still 5 carbons

19. Number the carbons to give the branch the lowest number possible
As alkanes do not have a functional group the carbons are numbered to give the branch the lowest numbers possible.

20. Branch attached to carbon 2
By numbering your carbons in the main straight chain, it makes it easier to identify the branch and which carbon it is attached too.
Branch attached to carbon 2

21. Different Branches
Methyl --- CH3
Ethyl -----C2H5

22. Systematic Naming
2-methylbutane

24. 3,3-dimethylhexane Di = 2 methyl groups , = used between numbers
3,3= the carbons which the methyl branches can be located

25. Systematically Naming Alkenes
Same rules as alkanes
Functional group the (C=C) gets first priority when numbering the carbons.
C=C gets lowest numbers before branches

26. Position of C=C The position of the C=C must be stated. hex-1-ene
The one tells us that the C=C comes after carbon 1

28. 5-methyl hex-1-ene

29. Uses/Properties of Alkanes
Physical Properties in BRANCHED ALKANES
Have higher Bp’s
Higher Volatility (evaporate easier)
(Compared with straight chain alkanes)
Uses of Branched Alkanes
Petrol manufacture. Used to improve how smoothly a fuel burns. Branched alkanes burn more smoothly than straight chain alkanes
For a fuel to burn it must vaporise and mix with air so volatility important too. In winter more volatile compounds are added to ensure the petrol vaporises easier.

30. Uses of Cycloalkanes Have higher mp’s and bp’s compared to alkanes
Used in petrol (like branches alkanes) as burn more smoothly than alkanes
Solvents for paints and varnishes

31. Isomers
Branched chain alkanes
Alkenes
Cycloalkanes

32. Drawing Isomers - Alkanes
Must always be an alkane
Can’t draw alkenes, or cycloalkanes
Make a branch
Must not be on the first or last carbon
If it has a branch – draw a straight chain alkane
Write the molecular formula
Does it have the same number of carbon and hydrogen
Systematically name the structure
This is a good way to check you have not just drawn the same structure twice

33. Drawing Isomers - Alkenes
Move the position of the double bond
Remember the double bond always gets given the lowest number so can only do this once or twice
Need to have at least 4 carbons before can move the C=C

34. Drawing Isomers - Alkenes
Add a branch
Remember can’t be on first or last carbon
Watch out for the carbons round the double bonds.
Remember carbon only makes 4 bonds
Draw a cycloalkane
Alkenes and cycloalkanes have the same general formula so they are isomers of each other.

35. Are these Isomers?? Check the molecular formulas
Do they have the same number of carbons and hydrogens
Is the structure different
This can be easily checked by systematically naming the compounds.

36. Reactions Combustion ( Reacting with oxygen)
Combustion of any Hydrocarbon produces CO2 and H2O
Colourless liquid goes cloudy.
ice water
limewater
burning gas
suction pump

37. Addition Reactions
Involves the breaking of a carbon to carbon double bond.
Small molecule added across double bond.
E.g. H2O, H2, Br2. HBr