Chemistry AS Unit 1

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Chemistry AS Unit 1
2012-05-10 06:11:41

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  1. Define: Relative Atomic Mass
    The average mass of an atom of an element, taking into account all of its naturally occuring isotopes, in comparison to 1/12 of the relative mass of an atom of carbon-12
  2. What are the advantages of high resolution mass spectrometry?
    You can identify different molecules which have very similar Mr values.
  3. Why are atoms vapourised before entering the spectrometer?
    To allow them to be ionised by the electron gun.
  4. How are atoms ionised in the mass spectrometer?
    An electron gun knocks off an electron (rarely 2) from the outer levels of the gaseous atoms. This forms 1+ ions usually.
  5. How are ions accelerated in the mass spectrometer?
    The ions are attracted to a negatively charged plate, and they therefore accelerate. The plate has a slit in it and therefore forms the ions into a straight beam.
  6. Describe the deflection phase of the mass spectrometer.
    A magnetic field is at right angles to the direction of travel of the ions. This therefore deflects the positively charged ions around the corner, should they have the correct m/z ratio for that strength of magnetic field.
  7. How is an ion detected in the mass spectrometer?
    The ion accepts electrons from the detector, therefore losing its positive charge. A current is produced which is proportional to the abundance of that ion in the sample.
  8. What is electronegativity?
    The ability to attract the shared pair of electrons in a covalent bond.
  9. How does Electronegativity increase?
    Diagonally up and accross the table.
  10. What does electronegativity depend on?
    The nuclear charge (amount of protons) and the amount of sub-level shielding.
  11. Where are the s,p,d and f blocks?
    Group 1+2 Metals, Non-metals, Transition Metals, Lanthanides and Actinides respectively.
  12. How does reactivity change down the s block?
    They get more reactive.
  13. How does the reactivity of p-block elements change down the group?
    The reactivity decreases down the group.
  14. What type of bonds do all metals form with one another?
    Metallic bonds.
  15. What is the structure of silicon?
    A giant covalent structure, similar to diamond.
  16. Why does the melting and boiling points of the metals increase from group 1-3?
    The strength of metallic bonds increase as they give up more electrons and producing a higher charge difference.
  17. What affects the melting/boiling point of the elements in group 4-7?
    The structure and therefore the vdw forces affect this. Silicon forms a giant covalent structure and so has no intermolecular forces, but requires a lot of energy to break many strong covalent bonds. Sulphur forms S8 and has a higher boiling point than P4 which has a higher boiling point than Cl2.

  18. Why do atomic radii decrease across the period?
    The increased nuclear charge leads to a stronger attraction to its electrons, which therefore decreases the atomic radius.
  19. Why do the atomic radii increase down the group?
    The outer main electron level is further away.
  20. First ionisation increases across the period. Why?
    There is a stronger nuclear charge which leads to a stronger attraction to their electrons.

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