Learning objectives

Introduce hydrocarbons, alkanes and the IUPAC nomenclature for alkanes and alkyl groups.

To understand the concept of isomers.

Hydrocarbons

The simplest organic

chemicals

What elements do you think they contain?

Bonds

How many bonds can a Carbon atom make?

How many bonds can a Hydrogen atom make

What will the formula be for the simplest hydrocarbon?

What is it called?

Carbon can form single, double and triple bonds with other carbon atoms so starting to build chains

Alkanes

These are the simplest family of hydrocarbons

All carbons linked by single C-C bonds

Widely used as fuels

Obtained by fractional distillation of crude oil

They are one of three families of hydrocarbons known as Aliphatic hydrocarbons – all of which only contain 2 elements.

Alkanes

Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane And so on

CH4

C2H6

C3H8

C4H10

Work out the empirical formula

Name Formula

Bigger Alkanes

11 12 13 14 15 20 21 22 30 31 40 50 100

Undecane Dodecane Tridecane Tetradecane Pentadecane Icosane Henicosane Docosane Triacontane Hentriacontane Tetracontane Pentacontane Hectane

No. of carbons name

What would be the names of straight chain alkanes containing 33 and 47 carbons?

Isomers

Butane upwards have isomers

Methane, ethane and propane do not have isomers

Isomers may have different properties

These molecules of the same formula but different shape are called isomers.

As the chains get longer there are more ways that they can be put together.

Butane isomers

The number of possible isomers increases with chain length

Butane (4) Pentane (5) Hexane (6) Heptane (7) Octane (8) Nonane (9) Decane (10) Pentadecane (15) Icosane (20) Tetracontane (40)

2 3 5 9 18 35 75 4347 366 319 62 491 178 805 831

Name and (no. of carbons)

Number of possible isomers

Naming isomers

A nightmare

Easy with pentane C5H12 which has 3 isomers

Straight chain is n-pentane

1 methyl side branch is isopentane

2 methyl side branches is Neopentane

Draw these so you are clear what we are talking about

After this it stops

Types of formulae

There are four ways of showing formulae of organic compounds

Look at these examples for decane 1. Molecular formulae: C10H22

2. Condensed structural formulae: CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

3. Structural formulae

4. Line structure:

Applying the IUPAC rules

1 Pick out the longest continuous branch and name it thus.

2 Identify the substituent groups attached to the parent chain and name them

3 Number the chain in the direction that gives the lower number to the first substituent group

4 Write the name of the compound starting with the number of the first substituent and then its name followed by any other substituents’ – number and name

5 name substituents in alphabetical order. E.g. 3 ethyl 2 methyl heptane

6. Use prefixes di, tri etc. to indicate 2, three or more of the same substituent

Alkyl groups

These are what we call the side chains.

They have one less hydrogen than the alkane with the same number of carbons

E.g. Methane has CH4

As a side chain it has CH3 and is known as a methyl group.

To name alkyl groups simply drop the ending ane and add yl and remove one hydrogen from the formula.

Other side groups

You can have halogens

Cl – chlorine becomes chloro

Br – Bromine becomes bromo

I – Iodine become iodo

F – fluorine becomes fluoro

Other options include aromatics – see later lessons and metals such as Iron, copper etc.

Plenary

Draw or use the models to make:

Hexane

2 methyl pentane

2,3, methyl heptane

4 ethyl nonane

2chloro butane

1chloro 3 methyl hexane

Name the six molecules the teacher has drawn on the board.

Themes for investigating: Aliphatic Hydrocarbons

1• How do physical and chemical properties change

with increased chain length?

2.• What are the chemical properties of double and

triple carbon-carbon bonds?

3.• How do we name alkanes, alkenes and alkynes?

4.• What are the main uses of alkanes, alkenes and

alkyne?s

5.

• What are the cycloaliphatics and how are their properties different from straight chain hydrocarbons?

Product of investigation-

1. Each of you will form a new group to share what you have learnt and this you will show on a poster.

2. Each group will develop an activity to help reinforce learning with the whole class.

3. Each group will provide a presentation to give to the whole class

4. The class will complete 5 exercises based on these five themes.

5. Members of each group will be responible for helping students to clarify any further doubts once the marked work is returned to them.

Rubric

Marks

Poster (individual)The part you contributed

Presentation (team)

Investigation (individual)

Learning activity (group)

Clarification of doubts. Individual

2 very weak Very muddled

Never on task

No help cannot

4 Some key points

Somre areas understandable

Mostly on task but rated poorly by captain

Could help but very boring

Has some idea

6 Mostly there Most of information correctly included

Good rating by captain

Good but not much fun

Basically correct but questioner remains confused

8 Fully covered Comprehensive and correct

Fully on task excellent rating by captain

Good and interesting

Helps