Atomic Structure

• What are the three sub-atomic particles?

  Proton, neutron, electron
• Where are protons and neutrons located in an atom?

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

  1
• What is the relative charge of a neutron?

  0
• What is the relative mass of an electron?

  1/1840
• How is an atom of Lithium represented?

  $^{7}_{3}Li$
• What does the atomic number (Z) represent?

  Number of protons in the nucleus
• What is the mass number (A) of an atom?

  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?

  They have the same electronic structure
• How can isotopes differ physically?

  They have different masses
• What is the purpose of a mass spectrometer?

  To 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 is the first step in a mass spectrometer?

  Ionisation
• What technique is used in electron impact ionisation?

  Firing high energy electrons at a sample
• What happens during electron impact ionisation?

  An outer electron is knocked out
• What is the process of electro spray ionisation?

  Sample is dissolved and injected as a mist
• What occurs at the tip of the needle in electro spray ionisation?

  The 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
• What happens to positive ions in the acceleration area?

  They are accelerated by an electric field
• How does the mass of ions affect their velocity in the flight tube?

  Lighter ions move faster than heavier ions
• What is detected in the detection area of a mass spectrometer?

  Current generated by ions
• What does the size of the current in the detection area indicate?

  Proportional to the abundance of species
• What is the relationship between kinetic energy and velocity for particles?

  Velocity depends on mass at constant kinetic energy
• How do you calculate the time of flight for an ion?

  $t =$$\frac{d}{v}$
• What is the mass of one ion of $^{59}Ni^+$?


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


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

  Mass-to-charge ratio
• What is the relative atomic mass (R.A.M) based on?

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

  $R.A.M =$ \frac{\Sigma (\text{isotopic mass} \times \text{% abundance})}{100}
• What is the R.A.M of magnesium given the isotopes and their abundances?

  $24.3$
• How do you calculate the percentage abundance of isotopes?

  $63.55 =$$y \times 63 +$$(1-y) \times 65$
• What is the relative atomic mass of tellurium based on given data?

  $127.8$
• What isotopes does chlorine have?

  Cl$^{35}$ and Cl$^{37}$
• What isotopes does bromine have?

  Br$^{79}$ and Br$^{81}$
• What is the difference between electron impact and electro spray ionisation?

  • Electron impact: used for low mass, can fragment
  • Electro spray: used for larger molecules, no fragmentation
• What is the parent ion in mass spectrometry?

  The peak representing the complete molecule
• What happens to the peak in electro spray ionisation?

  It equals the mass of the MH+ ion