Quick Fire Round of Questions How many bonds does Carbon have around it? What does saturated mean? What is the general formula for alkanes? How many carbons are in octane? How many carbons are in butane? What structure/shape do carbon atoms actually have? Can you list the first ten alkanes?

Homologous Series Chemical Families

Like families they have things in common but they are not identical All the members of each homologous series have 5 things in common

Homologous Series A family of compounds like the alkanes, which have a lot of similar properties is referred to as a HOMOLOGOUS SERIES. A homologous series can be defined as A series of compounds of uniform chemical type. Showing gradations in physical properties. Having a general formula for all its members. Having a similar method of preparation. Each member differing from the previous member by a CH2 unit.

Alkenes Alkenes are our 2nd group of hydrocarbons. They contain a double bond. Ie) Double carbon to carbon bond. They are unsaturated. How many carbons will the first alkene have? General formula for alkenes = CnH2n

Drawing alkenes How many electrons are being shared in a double bond? C=C What do you think this alkene is called? Naming Alkenes All alkenes end in ENE. The first part of an alkene is determined by the number of carbon atoms. If I have 4 carbons what will the alkene be called?

Task Work in groups to come up with as many similarities/differences between alkanes and alkenes. Alkanes have a single bond where as alkenes have a double bond. Alkanes are saturated, alkenes are unsaturated. Both are hydrocarbons. They have a different general formulas. Both are named using the same methods.

Alkanes and alkenes Which bond is the strongest? The double bond is much stronger that the single bond. Why do you think this it? More electrons are being shared. Which do you think is more reactive alkanes or alkenes? Alkenes are more reactive that alkanes. The double bond makes them more reactive carbon with all single bonds is more stable and therefore less reactive.

Unsaturated hydrocarbons Hydrocarbon = contains hydrogen and carbon only Unsaturated = contains at least one double or triple bond. Unsaturated compounds react quickly with [a] bromine [red/brown] [b] acidified KMnO4 [purple] and decolourise them. [Saturated only have single bonds]

Making ethene Ethanol  Ethene + H2O Aluminium oxide is needed for this reaction to take place. Aluminium oxide is a white powder and is also a dehydrating agent. It is a catalyst for the reaction. What is a catalyst? A catalyst is a substance that changes the rate of a chemical reaction without getting used up in the process.

Ethene Ethene is very important in industry as it is the starting substance for many materials. An example is polythene which is a form of plastic. It can also be used to make PVC.

Combustion Burns to form CO2 and H2O C2H4 + 3 O2 = 2 CO2 + 2 H2O Yellow flame normally blue or non-luminous flame if there is excess oxygen reasonably explosive lots of heat produced – very exothermic

Lets just look at electrons for a moment H H C C What does each of these lines represent? H H Lets just look at electrons for a moment Lets put in the electrons – one from each atom A Bond – a shared pair of electrons

Now lets go back to our ethene molecule Two things [1] The electrons can repel because like charges repel What does this represent? What can happen now? or [2] The electrons can form a bond An electron Now lets go back to our ethene molecule

H H H H H H H H C C C C C C C C H H H H H H H H What happens to the two electrons now? What happens to the two electrons now? Suppose I supply a dart of energy that breaks one of the two bonds in the double bond. Suppose I supply a dart of energy that breaks one of the two bonds in the double bond of another ethene. The bond has been broken so they repel each other and move to opposite sides of the molecule The bond has been broken so they repel each other and move to opposite sides of the molecule Now a new bond forms between these 2 electrons and the two molecules are joined together

δ- δ+ δ+ Solubility Alkenes are insoluble in water Why? Because water is a polar compound Ethene is non-polar Like dissolves like Non-polar dissolves non-polar, and polar dissolves polar Ethene dissolves in cyclohexane or benzene [non-polar liquids] δ+ δ+

Naming of complex Alkenes and Isomers This process is much the same as the naming of alkanes. Count the number of carbons. Say for example there was 5 = Pentene Number to carbons – This time you are taking the position of the double bond into account. Number the chain starting at the end NEAREST to the double bond.

Isomers Isomers occur - same chemical formula but different structural formulae Occur due to [a] the position of the double bond hex-1-ene and hex-2-ene [b] branching e.g. 4 methyl pent-1-ene and hex-1-ene these three compounds are all isomers

Examples Draw 3 isomers of Butene Hexene

Isomers of Butene There are 3 isomers of Butene But-1-ene But-2-ene Methylpropene As we mentioned in the previous lesson some structures can also have a cyclic shape for example Hexene.

Properties of ethene Ethene is a non polar substance. Therefore it doesn’t dissolve in water. It will dissolve in organic solvents cyclohexane and chloroform. As a result of this the gas can be collected over water. It is a colourless gas. It will burn with a luminous flame. Will under go a combustion reaction to produce Carbon Dioxide and Water. C2H4 + 3O2  2CO2 + 2H2O Limewater turns milky therefore showing that CO2 is produced when ethene is burned in air.

Learning Objectives Introduction to alkynes Introduction to aliphatic and aromatic hydrocarbons. Benzene and its alternating double and single bonds.

Alkynes Alkynes like alkenes are unsaturated. Alkynes have a triple bond. How many electrons are being shared in a triple bond? Do you think this bond is stronger or weaker than a double or a single bond? A triple bond is the strongest bond as 6 electrons are being shared. Do you think that alkynes are reactive? Alkynes are extremely reactive as the carbon atoms want to get back to having 4 single bonds.

Alkynes General Formula CnH2n-2 The only alkyne that we have to focus on is ethyne C2H2. Another name for ethyne is acetylene. This gas can be used in oxyacetylene welding and cutting. It is used for this purpose as when it is burned it can reach temperatures of over 3000 degrees Celsius.

Can you draw and name the first three alkynes?

Preparation of ethyne

Set up the apparatus as shown in the diagram Add a few pieces of calcium carbide to the Buchner Flask Add water a few drops at a time Collect the gas produced but discard the first flask as this will contain mostly air

Test for production of ethyne Combustion: Burns with a luminous smoky flame which results in soot being formed Decolourises bromine water Decolourises acidified potassium permanganate

Aliphatic hydrocarbons. An aliphatic compound is an organic compound that consists of open chains of carbon atoms and closed chain compounds (rings) that resemble them in chemical properties. What are examples of aliphatic hydrocarbons?

Benzene A benzene ring has the formula of C6H6. If a compound contains a benzene ring then it as an AROMATIC COMPOUND. Aromatic Compounds are compounds that contain a benzene ring structure in their molecules. Some but not all aromatic compounds have pleasant smells.

Benzene Benzene is highly unsaturated and it was predicted that it would be extremely reactive due to the presence of three double bonds. It was predicted that benzene had alternating double and single bonds. However benzene was found to be very UNREACTIVE. It did not decolourise potassium permanganate.

Benzene Instead of having alternating double and single bonds benzene has bonds that are half way between double and single bonds. All the bonds in benzene are the one length. Therefore there is a mixture of sigma and pi bonding present in benzene.

Therefore carbon has 6 electrons that are not in a bond Therefore carbon has 6 electrons that are not in a bond. These are known as VALENCE electrons. These valence electrons belong to the whole molecule instead of being localised. (They are floating around the molecule, they don’t belong to any carbon atom in particular). This is what gives benzene its extra stability and accounts for its unreactivity.

Crude Oil. Crude oil is also called petroleum. Depend on crude oil for fuels for transport, heating and to produce a wide range of chemicals. Crude oil is a FOSSIL FUEL – Formed from the bodies of sea creatures that died millions of years ago.

Fractional Distillation https://www. twig-world

Fractional Distillation of crude oil. Crude oil pumped from under the ground or the sea is of little use to us. We need to separate it into a number of useful mixtures and this process is called fractional distillation. This process involves heating the crude oil and separating the various mixtures on the basis of their boiling points. Each one of these mixtures is called a FRACTION.

The process of Fractional Distillation Crude oil is heated in a furnace and enters into the fractionating column as a partially vaporised material. The fractionating column has the highest boiling point at the bottom and it decreases as you move upwards. Therefore the larger hydrocarbons with high boiling points turn into liquid near the bottom. The smaller hydrocarbons stay as gases and rise up along the column.

Fractional Distillation Column Top of the column hydrocarbons like methane, ethane propane and butane are gases. They are know as REFINERY GAS or PETROLEUM GAS. These compounds are odourless therefore compounds called MERCAPTANS are added to give an unpleasant smell.

Fraction Refinery gas Petrol/Light Gasoline – Motor Fuel C5-C10 Naptha – Used in medicine and plastics C7- C10 Kerosene or parrafin = Aviation fuels and used in stoves Diesel Oil – More difficult to vaporise than the rest. Fuel for buses and trains. Lubricating Oil – Viscous Liquid. High boiling point therefore can’t be vaporised easily therefore not used as a fuel. It reduces wear of engines. Fuel Oil – Can be used as fuel by spraying onto burners as a fine mist of small droplets. Bitumen – Used as tar and can also be used in waterproofing and roofing.

Lubricating oil, fuel oil and Bitumen are known as the residue fraction as they are the fractions that are left over when the volatile fractions boil off. Volatile = Low boiling point.