1.1 - Atomic Structure

• What are the three sub-atomic particles?

  Proton, neutron, electron
• Where is the proton located in an atom?

  In the nucleus
• What is the relative mass of a neutron?

  1
• What is the relative charge of an electron?

  -1
• How is an atom of Lithium represented?

  $\frac{7}{3}Li$
• What does the atomic number, Z, represent?

  Number of protons in the nucleus
• What is the mass number, A?

  Total number of protons and neutrons
• How do you calculate the number of neutrons in an atom?

  Number of neutrons = A - Z
• What are isotopes?

  Atoms with the same protons, different neutrons
• Why do isotopes have similar chemical properties?

  Same electronic structure
• How do isotopes differ in physical properties?

  Different masses
• What is the purpose of a mass spectrometer?

  Identify elements and isotopes in a sample
• What are the four essential steps in a mass spectrometer?

  1. Ionisation
  2. Acceleration
  3. Flight Tube
  4. Detection
• What happens during ionisation in a mass spectrometer?

  The sample is converted into ions
• What is electron impact ionisation?

  Firing high energy electrons at a sample
• What is the result of electron impact ionisation?

  Positive ions with different charges
• What is electrospray ionisation?

  Sample dissolved in solvent, forms mist
• What occurs at the tip of the needle in electrospray ionisation?

  Sample gains a proton from the solvent
• Why must the mass spectrometer be under a vacuum?

  To prevent air particles from ionising
• What are the four areas of a mass spectrometer?

  1. Ionisation area
  2. Acceleration area
  3. Ion drift area
  4. Detection area
• How do positive ions behave in the acceleration area?

  They are accelerated by an electric field
• What does the kinetic energy equation represent?

  KE = ½ mv²

  
• How do lighter and heavier particles differ in velocity?

  Lighter particles move faster than heavier ones
• How do you calculate time of flight in a mass spectrometer?

  t = d/v
• What is the mass of one ion of 59Ni+?

  $9.797 \times 10^{-26} \text{ kg}$
• How long does one ion of 59Ni+ take to travel 0.8000 m?

  $1.771 \times 10^{-5} \text{ s}$
• What does m/z represent in mass spectrometry?

  Mass/charge ratio of ions
• What is the relative atomic mass (R.A.M)?

  Weighted average of all isotopes
• How do you calculate R.A.M from isotopic mass and abundance?

  R.A.M = Σ(isotopic mass x % abundance)/100
• What is the R.A.M of magnesium with given isotopes?

  24.3
• What is the charge and mass number for 24Mg+?

  Charge +1, mass number 24
• How do you calculate the R.A.M of tellurium from relative abundance?

  R.A.M = [(124x2) + (126x4) + (128x7) + (130x6)]/19
• What is the R.A.M of copper with isotopes 63-Cu and 65-Cu?

  63.5
• What are the percentage abundances of 63-Cu and 65-Cu?

  72.5% and 27.5%
• What isotopes does chlorine have and their abundances?

  • Cl35 (75%)
  • Cl37 (25%)
• What isotopes does bromine have and their abundances?

  • Br79 (50%)
  • Br81 (50%)
• What is the role of mass spectrometers in planetary space probes?

  Identify elements on other planets
• What happens to molecules in a mass spectrometer with electron impact ionisation?

  They often break up into fragments
• What is the parent ion in mass spectrometry?

  Peak with the largest m/z value
• What occurs when a molecule is ionised by electrospray ionisation?

  No fragmentation occurs