Topic 4

• All organic chemicals contain carbon, and most contain hydrogen, which are hydrocarbons. Some also contain nitrogen or oxygen.
• Carbon forms 4 bonds.
• saturated - compound containing only single bonds between carbons
• unsaturated - compound containing one or more double bonds between the carbons
• Alkanes and cycloalkanes only have single bonds so they are saturated.
• displayed formula - shows every atom and bond separately

  
• structural formula - groups all of the atoms joined to a carbon together

  
• skeletal formula - only shows bonds between carbon atoms and functional groups

  
• molecular formula - only show the number of each type of atom, without the structure e.g. C3H8
• empirical formula - simplest whole number ratio of atoms of each element in a compound e.g. CH2
• functional group - an atom or group of atoms in a molecule that is responsible for its chemical reactions, and giving the compound some distinctive and predictable properties
• homologous series - a family of compounds with the same functional group, which differ in formula by CH2 from the next member
• general formulas

  • alkane CnH2n+2
  • alkene CnH2n
  • halogenoalkane CnH2n+1X
  • alcohol CnH2n+1OH
• number of carbon atoms

  1 - meth

  2 - eth

  3 - prop

  4 - but

  5+ is normal e.g. pent, hex
• Prefixes and suffixes are added to show the functional group. Prefixes are put in alphabetical order. Prefixes are multiplied when there are multiple identical functional groups e.g. 2 - di, 3 - tri, 4 - tetra
• Locants are numbers that show which carbon atom, in the longest chain, has a functional group attached to it. The lowest locate number is used for the suffix functional group.
• structural isomers - compounds with the same molecular formula, but different structural formulae
• chain isomerism - compounds that have the same molecular formula but different carbon chain
• functional group (position) isomerism - functional groups in compounds, with the same molecular formula, are in different positions as they are attached to different carbons
• cycloalkanes - a structural difference of alkanes where the carbons form a ring rather than a single chain so they don't have as many hydrogen atoms
• An addition reaction is when 2 reactants combine to form 1 product e.g. C2H4 + Br2 -> C2H4Br2
• A substitution reaction is when 2 reactants combine to form 2 different products. An atom or group of atoms is replaced in the reactants e.g. C2H5Br + OH- -> C2H5OH + Br-
• An oxidation reaction is when 1 organic compound is oxidised by an inorganic reagent. The compound either gains oxygen atoms or loses hydrogen atoms.
• A reduction reaction is when 1 organic compound is reduced by hydrogen and a catalyst, or by an inorganic reagent. The compound either loses oxygen atoms or gains hydrogen atoms.
• In an addition polymerisation, large numbers of reactant molecules (monomers) combine to form 1 large product molecule (polymer).
• In homolytic fission, the shared pair of electrons in the covalent bond divide equally between the two atoms. Each atom keeps one electron, making it a free radical. Free radicals have an unpaired electron and are uncharged. It happens when the two bonded electrons are identical or have similar electronegativities.
• In heterolytic fission, the shared pair of electrons in the covalently bond are kept by one atom. The atom with the electrons is negative, and the atom without the electron is positive. It happens when the two bonded atoms have different electronegativities, so the one with the higher electronegativity keeps the electrons.
• electrophiles - positive ions are attracted to a region of high electron density in another molecule that are missing a lone pair of electrons
• nucleophiles - attracted to molecules with a positive charge, and have a lone pair of electrons
• hazard - a substance that could cause harm to a user
• risk - chance of a hazard causing harm
• risk assessment - identification of hazards involved in carrying out a procedure and control measures to reduce the risk of these hazards
• health hazard : skin rashes, eye damage, ingestion
• corrosive : skin burns, permanent eye damage
• flammable : catches fire if heated or in contact with a flame
• acute toxicity : life threatening effects
• Different control measures are needed for different experiments, for example:

  • type of eye protection
  • gloves
  • caps on bottles
  • keep substance away from heat
  • procedure if substances go on floor or skin
• Crude oil is a complex mixture of hydrocarbons. In order to separate it, it is heated in a furnace and turned into vapour, which is passed into a distillation column where there is a temperature gradient. Different fractions condense at different heights, depending on their boiling points. The molecules are larger as they go down the column. Some fractions stay gaseous at the top.
• Cracking is the conversion of long chain molecules into short chain molecules so that they are more useful. There is thermal cracking, steam cracking and catalytic cracking.
• Catalytic cracking involves passing heavier fractions through a heated catalyst, usually a zeolite which is a compound of aluminium, silicon and oxygen.