Unit 2.4

• Advantages of fossil fuels:

  They are available in a variety of forms and at all times. They are reliable as they don't depend on weather conditions. They are currently widely available and current infrastructure is set up around fossil fuels.
• Disadvantage of fossil fuels:

  They are non-renewable and easily obtained sources are running out as reserves are being used faster than new ones are formed. Increases global warming (due to CO2 emitted during combustion) causing melting ice caps, unpredictable weather patterns, etc. Acid rain is caused by sulfur impurities (which form SO2) in fossil fuels. Incomplete combustion of fossil fuels can form carbon monoxide which is toxic to humans.
• Alkane are saturated hydrocarbons with no carbon double bonds
• Alkenes are unsaturated hydrocarbons with one or more carbon double bonds
• Halogenoalkanes are compounds in which one or more hydrogens in an alkane have been replaced by a halogen
• Alcohols contain an OH as the functional group
• Carboxylic acids have COOH as the functional group
• The larger the hydrocarbon, the higher the boiling point
• Hydrocarbons are simple covalent molecules consisting of carbon and hydrogen atoms, which have similar electronegative values. This means that only temporary dipoles are present between the molecules. These are weak intermolecular forces.
• Boiling points of hydrocarbons depend on both the size and shape of the molecule. Different structural isomers will have different boiling temperatures because they have different surface areas that can be in contact.
• The more branches a hydrocarbon has, the more spherical in shape they are and so the less surface contact, therefore they have low boiling points. Straight chains have more surface contact and so have higher boiling points.
• The less surface contact in a hydrocarbon means weaker temporary dipoles between molecules and so less energy is required to separate them. This results in a lower boiling temperature.
• Hydrogencarbons which can form hydrogen bonds with water molecules are soluble. Alcohols and carboxylic acids have OH groups which can hydrogen bond. However, the larger the molecule, the less soluble it becomes, despite being able to hydrogen bond.
• As the size of a hydrocarbon increases, the molecule exerts such a large hydrophobic effect that the compound is no longer soluble.
• There are 3 types of isomerism, chain isomerism, functional group isomerism and positional isomerism.
• Chain isomers are isomers which have a different chain arrangement, for example one isomers may contain a straight carbon chain whereas one may be branched.
• Functional group isomers is when the functional groups are different, so one isomers may be an alcohol and another may be a carboxylic acid.
• Positional isomers is whne the functional groups are attached to different carbons.
• An electrophile is a species which is electron deficient, and will accept a lone pair of electrons.
• A nucleophile is a species which contains a lone pair of electrons, which can be donated to electron deficient species.
• Radicals are species with unpaired electrons