module 4.1

• homologous series: series of organic compounds that have the same functional group with successive members differing by CH2
• functional group: a group of atoms responsible for the characteristic chemical reactions of a compound

  detailed in either the suffix (end) if it is the most important group or the prefix (start) if it is an additional functional group
• alkyl group: a group with the general formula CnH2n+1
• aliphatic: hydrocarbon with carbon atoms joined together in straight or branched chains
• alicyclic: hydrocarbon with carbon atoms joined together in a ring structure
• aromatic: contains at least one benzene ring
• saturated: organic compound that only has C-C single bonds 
• unsaturated: an organic compound which contains at least one C=C double bond, a C≡C triple bond or an aromatic ring 
• alkane general formula

  CnH2n+2
• alkene general formula

  CnH2n
• alcohol general formula

  Cn2n+1OH
• structural isomers: same molecular formula different structures (or structural formulae)
• functional group isomers: compounds with the same molecular formula but with atoms arranged to give different functional groups
• homolytic bond fission: happens when each bonding atom recieves one electron from the bonded pair, forming two radicals 
• heterolytic fission: happens when one bonding atom recieves both electrons from the bonding pair
• radical: species with one or more unpaired electrons
• curly arrow: models the flow of electron pairs during reaction mechanisms
• alkanes are saturated hydrocarbons containing single C-C and C-H bonds as σ-bonds
• describe the formation of the σ bond in alkanes

  carbon 2s and 2p atomic orbitals make 4 hybrid orbitals (sp³)

  two sp³ orbitals in neighbouring carbon atoms overlap to produce a C-C σ bond between the atoms

  remaining three sp³ orbitals on each carbon atom overlap with 1s orbitals from three separate hydrogen atoms to produce three C-H σ bonds
• the carbon atom in alkanes is tetrahedral and the bond angle is 109.5°

  the shape is tetrahedral as a result of the four bond pairs of electrons equally repelling
• as an alkane chain length gets longer its relative molecular mass increases

  larger molecules have more surface area contacts between adjacent molecules.

  this increases the number of induced dipole-dipole forces

  so more energy is needed to overcome the intermolecular attraction in order that the alkane can change state
• structural isomers of alkanes have different boiling points. the more branched a compound is, the fewer surface area interactions there are between molecules - this is because the molecules cannot fit together as neatly

  therefore branched molecules have fewer induced dipole-dipole attractions compared to the straight-chain isomer with the same molecular formula

  this leads to branched molecules having a lower boiling point than the equivalent straight-chain isomer
• alkanes have a low reactivity with many reagents

  all the covalent bonds in alkane molecules have high bond enthalpies - a large amount of energy is required to break the bonds

  the carbon-hydrogen σ bonds have very low polarity because the electronegativities of carbon and hydrogen are almost the same
• in excess oxygen alkanes will burn with complete combustion

  CH4 + 2O2 → CO2 + 2H2O
• alkanes readily burn in the presence of oxygen. this combustion of alkanes is highly exothermic, explaining their use as fuels.
• 2CH4 + 2 1/2 O2 → CO + C + 4H2O

  2CH4 + 3 1/2 O2 → CO2 + CO + 4H2O

  3CH4 + 4 1/2 O2 → CO2 + CO + C + 6H2O

  if there is a limited amount of oxygen then incomplete combustion occurs, producing CO (which is very toxic) and/or C (producing a sooty flame)
• CO is toxic to humans as CO can form a strong bond with haemoglobin in red blood cells. This is a stronger bond than that made with oxygen and so it prevents the oxygen attaching to the haemoglobin.

  carbon monoxide is a highly toxic but odourless gas. it can cause death if it builds up in an enclosed space due to faulty heating appliances.
• limitations of radical substitution?

  further substitution could occur if another chloride radical collides with the product of propagation

  if the carbon chain is longer, a mixture of products forms as substitution occurs at different positions along the chain
• alkenes are unsaturated hydrocarbons containing a C=C bond comprising a π bond