Chemistry study guide compressed unit 2

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ZAREEFA K

Cards (700)

  • Homologous series

    A group of organic compounds with the same functional group in which each successive member increases by the unit -CH₂
  • Examples of homologous series and functional groups
    • Alkene (>C=C<)
    • Alcohol (-OH)
    • Halogenoalkane (-F, -Cl, -Br or -I)
    • Carboxylic acid (-CO₂H)
  • Characteristics of a homologous series
    • A particular or general formula which applies to all members
    • Each successive member increases by the unit -CH₂
    • The members have very similar chemical properties
    • The physical properties change in a regular way
  • Empirical formula

    Shows the simplest whole number ratio of atoms of each element present in a compound
  • Molecular formula

    Shows the actual number of atoms of each element present in a molecule of a compound
  • The empirical formula is sometimes the same as the molecular formula
  • Structural formula

    Shows the arrangement of atoms in a molecule in a simplified form, either as a displayed formula or a condensed formula
  • More than 100 000 new compounds are made each year by research chemists, most of which are organic compounds containing rings and branches (side chains)
  • Structural formula

    A formula showing all atoms and bonds in a molecule
  • Condensed formula

    A formula where bonds are not shown
  • Structural formulae

    • HH
    • H-C-C-H
    • HH
    ethane (displayed)
    HHH
    1. C-C-C
    HHH
    H
    propylamine (displayed)
  • Condensed formulae

    • CH2CH3
    ethane
    CH3CH2CH3NH2
    propylamine
  • With chain hydrocarbons, the condensed formula can be further condensed to show the actual structure
  • In condensed formulae, side branches coming off the main chain are shown in brackets
  • Displayed and condensed formulae for methylbutane

    • HHHH
    1. H
    HH
    methylbutane (displayed)
    CH(CH3)CH2CH3
    methylbutane (condensed)
  • Displayed and condensed formulae for cyclohexane
    • H
    H
    H
    H
    H
    H
    H
    cyclohexane (displayed)
    cyclohexane (condensed)
  • Displayed and condensed formulae for benzene

    • H
    I
    H
    H
    benzene (displayed)
    C6H6
    benzene (condensed)
  • The ring inside the hexagon in benzene represents the delocalised ring of electrons
  • Homologous series

    A group of organic compounds with the same functional group in which each successive member increases by the unit -CH2
  • Empirical formula

    The simplest whole number ratio of atoms of each element present in a compound
  • Molecular formula

    The actual number of atoms of each element present in a molecule of a compound
  • Alkanes

    Hydrocarbons with the general formula CnH2n+2
  • Combustion of alkanes

    1. Alkanes undergo combustion in excess oxygen or air to form carbon dioxide and water (in gaseous form)
    2. Incomplete combustion produces carbon monoxide (and/or carbon)
  • Cracking of alkanes

    1. Thermal decomposition of alkanes into shorter-chain alkanes and alkenes
    2. Carried out at 400-500°C using a catalyst of SiO2 and Al2O3
    3. Thermal cracking without a catalyst can also be carried out at 700-900°C
  • Halogenation of alkanes

    1. Reaction of alkanes with halogens like chlorine in the presence of UV light
    2. Substitution reaction where one or more hydrogen atoms are replaced by halogen atoms
  • Homolytic fission

    The two shared electrons in the bond are split equally between the two atoms
  • Heterolytic fission

    The two shared electrons in the bond are split unequally, with one atom keeping both pairs of electrons
  • Free radical substitution in alkanes
    1. Initiation: UV light causes Cl-Cl bond to break by homolytic fission
    2. Propagation: Methyl free radical attacks Cl2 to form more Cl free radicals, continuing the chain reaction
    3. Termination: Two free radicals combine to form a single molecule, stopping the chain reaction
  • Free radicals are atoms or groups of atoms with unpaired electrons
  • Fishhook arrows show the movement of a single electron, while curly arrows show the movement of an electron pair
  • The propogation mechanism

    1. H-C-C-H + Cl→ H-C•-C-H + HCl
    2. H-C•-C-H + Cl₂→ H-C-C-Cl + Cl•
  • Free radicals

    So reactive that they can attack the relatively unreactive methane
  • Propagation

    1. CH₄ + Cl• → CH₃• + HCl
    2. CH₃• + Cl₂ → CH₃Cl + Cl•
  • Termination

    1. CH₃• + Cl• → CH₃Cl
    2. CH₃• + CH₃• → CH₃CH₃
  • Alkanes

    • Undergo combustion to form carbon dioxide and water
    • Undergo cracking to form shorter-chain alkanes and alkenes
    • Undergo substitution reactions where one atom or group is replaced by another
  • Homolytic fission

    A bond breaks so that each atom retains one of the bonding electrons
  • Heterolytic fission

    A bond breaks so that one atom takes both bonding electrons
  • Curved arrow

    Shows the movement of an electron pair
  • Fishhook arrow

    Shows the movement of a single electron
  • Alkenes have the general formula C₂H₂n