1. Atomic Structure

• what is the relative mass of an electron?

  1/1840
• what is the formula for number of neutrons?

  A-Z
• what is an isotope?

  atoms with the same number of protons, but a different number of protons
• why do isotopes have very similar chemical properties?

  they have the same electron configuration
• what can a mass spectrometer be used to find?

  relative atomic mass
• what happens in the ionisation phase of TOF-MS?

  positive ions are formed, either by electrospray ionisation or electron impact ionisation
• what happens in electron impact ionisation?

  1. vaporised sample injected at a low pressure
  2. electron gun fires high energy electrons at the sample
  3. this removes an electron and forms a positive ion
• what happens in the acceleration phase of TOF-MS?

  ions accelerated in an electron field to a constant kinetic energy
• which ions travel at a faster speed?

  lighter ions
• what happens at the detector?

  ions hit the detector and remove an electron, forming a small electric current which is proportional to the abundance of the ions
• what is the use of TOF-MS in space?


  used to identify elements on other plants
• what is the principle quantum number?

  the shell number that an electron occupies
• what groups are in s block of the periodic table?

  1-2
• what groups are in the d block of the periodic table?

  transition metals
• what groups are in the p block of the periodic table?

  3-0
• what is first ionisation energy?

  the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive charge
• what are the main factors affecting ionisation energy?

  1. attraction of the nucleus
  2. distance of electrons from nucleus
  3. shielding
• why does first IE decrease down a group?

  distance from the nucleus increases and shielding increases so the attraction of the nucleus decreases
• why is there a general increase in first IE across a period?

  constant shielding but a greater nuclear charge
• where is there a small drop from Mg to Al?

  Al has valence electrons in a 3p sub-shell where Mg has valence electrons in a 3s sub-shell, and 3p is lower in energy
• why is there a small drop from P to S?

  a second electron in the 3p orbital in S causes spin-pair repulsion, making the second electron easier to remove