Chemistry Basic Concepts and Hydrocarbons

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Chemistry Basic Concepts and Hydrocarbons
2011-11-13 10:08:54
chemistry Basic Concepts Hydrocarbons

Basic Concepts and Hydrocarbons
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  1. What is a homologous series?
    A series of organic compounds with the same functional group but with each successive member differing by CH2
  2. What is a functional group?
    The part of the organic molecule responsible for its chemical reactions
  3. What is a hydrocarbon?
    A compound of hydrogen and carbon only
  4. What is a saturated and an unsaturated hydrocarbon?
    • Saturated: Has single bonds only
    • Unsaturated: contains a carbon-carbon double bond
  5. Members of the alkane series
    • 1. Methane
    • 2. Ethane
    • 3. Propane
    • 4. Butane
    • 5. Pentane
    • 6. Hexane
    • 7. Heptane
    • 8. Octane
    • 9. Nonane
    • 10. Decane
  6. Types of compounds
    • Alkane C-C
    • Alkene C=C
    • Halogenoalkane F, Cl, Br, I
    • Alcohol -OH
    • Aldehyde -CHO
    • Ketone C-CO-C
    • Carboxylic Acid -COOH
  7. Formulae
    • Empirical formula: simplest whole number ratio
    • Molecular formula: actual number of atoms of each element in a molecule
    • General formula: simplest algebraic formula e.g. CnH2n+2
    • Displayed formula: shows relative positioning of all the atoms
    • Structural formula: shows minimal detail for the arrangement e.g. CH3CH2CH2Br
    • Skeletal formula: simplified organic formula
  8. What is a structural isomer?
    Molecules with the same molecular formula but with different structural arrangements of atoms
  9. What is a stereoisomer?
    Compounds with the same structural formula but with a different arrangement of the atoms in space
  10. What is E/Z isomerism?
    A type of stereoisomerism in which different groups attached to each carbon of a C=C bond may be arranged differently in space because of restricted rotation of the C=C bond
  11. What is cis-trans isomerism?
    A special type of E/Z isomerism in which there is a non-hydrogen group and hydrogen on each C of a C=C bond. Cis, H on same side
  12. Covalent bond fission
    • Homolytic: the breaking of a covalent bond, with one of the bonded electrons going to each atom, forming two radicals. X-Y -> X. + Y.
    • Heterolytic: the breaking of a covalent bond with both of the bonded electrons going to one of the atoms. X-Y -> X+ + Y-
  13. What is a nucleophile and electrophile?
    • Nucleophile: electron pair donor
    • Electrophile: electron pair acceptor
  14. What is a radical?
    A species with an unpaired electron
  15. What is an addition reaction?
    • A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule
    • E.g. Ethene + Bromine -> 1,2-dibromoethane
  16. What is a substitution reaction?
    • A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms
    • E.g. Bromoethane + OH- -> Ethanol + Br-
  17. Crude Oil
    • Mixture of over 150 different hydrocarbons
    • Fractional distillation: the separation of the components in a liquid mixture into fractions which differ in boiling points
  18. Boiling points of alkanes
    • Chain length: increasing chain length, increases boiling point, more van der Waals' forces between the molecules in longer chains, takes more energy to separate them
    • Branching: same molecular mass, unbranched molecules have a higher boiling point, more points of contact for van der Waals' forces
  19. Combustion of alkanes
    • burning in a plentiful supply of oxygen
    • carbon dioxide and water is formed
  20. Incomplete combustion
    • burning in a limited supply of oxygen
    • such as in an internal combustion engine
    • carbon monoxide is formed
  21. Cracking
    • the breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes
    • catalytic cracking: uses a zeolite catalyst at about 450 degrees
    • many different possible equations for cracking
    • Branched alkanes: unbranched alkanes can be converted into branched alkanes using isomerisation
    • Cyclic hydrocarbons: reforming, alphatic hydrocarbons being converted into cyclic or aromatic hydrocarbons
  22. Fossil fuels
  23. Radical substitution of alkanes
    • a type of substitution reaction in which a radical replaces a different atom or group of atoms
    • UV radiation needs to be present
    • covalent bonds are broken by homolytc fission to form radicals with an unpaired electron
    • Mechanism: initiation, propagation, termination
    • Limitations: mixture of products are formed
  24. Alkenes
    • alkenes and cycloalkenes are unsaturated hydrocarbons (have atleast one C=C double bond)
    • General formula: CnH2n
  25. Double bond in alkenes
    • made up from a sigma bond and a pi bond
    • Formation of the double bond: sigma bond is formed between two carbon atoms by the overlap of orbitals, a pi bond is formed above and below the plane of the carbon atoms by sideways overlap off p-orbitals, the pi bond fixes the carbon atoms in place
    • pi-bond prevents rotation of the bond

  26. Shape of an alkene molecule
    • 3 regions of electron density around each carbon atom in the double bond
    • the pairs of electrons repel each other as far apart as possible to minimise repulsions
    • trigonal planar shape: bond angles 120 degrees
    • ethane is a flat planar molecule
  27. Addition reactons of alkenes
    • Hydrogenation: addition of hydrogen gas, catalyst of nickel, temperature 150oC
    • Halogenation: addition of halogens, room temperature
    • Test for unsaturation: adding bromine to a sample, if it contains an alkene the colour changes from orange to colourless
  28. Addition reaction of alkenes with hydrogen halides
    • produing a halogenoalkane
    • Unsymetrical alkenes:
  29. Addition reaction with steam
    • hydration of an alkene
    • high temperature and pressure
    • phosphoric acid catalyst
  30. Electrophilic addition in alkenes
    • Electrophile: electron pair acceptor
    • Curly arror: movement of an electron pair