PRACTICE QUESTIONS

• TWO DIFFERENCES IN ATOMIC MODEL PROPOSED BY RUTHERFORD AND THE CURRENT MODEL?

  1. Current model shows neutrons and protons in the nucleus
  2. Current model shows electrons in different orbitals
• TWO REASONS WHY IT IS NECESSARY TO IONISE ISOTOPES BEFORE ANALYSIS IN A TOF MASS SPECTROMETER?

  1. So ions can be accelerated by an electric field
  2. To make ions charged allow them to produce a current at the detector
• HOW ARE MOLECULES IONISED USING A TOF MASS SPECTROMETER?

  1. Sample dissolved in volatile solvent (e.g. water/ methanol)
  2. Injected through needle at high voltage
  3. Each molecule gains a proton
• EXPLAIN THE FIRST IONISATION ENERGIES FROM G1 TO G0?

  GENERAL TREND (G1 -> G0)

  • 1st ionisation energy increases
  • Higher proton number
  • Similar shielding
  • Stronger electrostatic attraction between nucleus and outermost electron

  DEVIATION (G2 -> G3)

  • G3 lower than G2
  • Outermost electron in p
  • Higher in energy than s

  DEVIATION (G5 -> G6)

  • G6 lower than G5
  • 2 electrons needed in p to pair
  • Pairing causes repulsion
• DO G2 OR G3 ELEMENTS HAVE LOWER FIRST IONISATION ENERGIES?

  • G3
  • outermost electron in p orbital
  • higher in energy
  • so easier to remove
• HOW DOES ELECTRON IMPACT IONISATION WORK?

  sample bombarded with high energy electrons causing it to lose an electron
• HOW DOES ELECTROSPRAY IONISATION WORK?

  high voltage applied, substance gains proton
• WHAT ARE SPECIES ACCELERATED BY IN A TOF MASS SPECTROMETER?

  electric field
• WHAT ARE IONS DEFLECTED BY IN A TOF MASS SPECTROMETER?

  magnetic field
• HOW IS A CURRENT GENEREATED IN A TOF MASS SPECTROEMTER?

  1. Positive ions hit detector
  2. Gain an electron from detector to ion
  3. Creating a current