Atomic structure

• What does the atomic number tell us about an element?

  The number of protons
• Define relative atomic mass.

  The average mass of an of an element relative to the 1/2 the mass of an atom of carbon-12
• Define an isotope.

  Different forms of the same element, which has the same number of protons but different number of neutrons.

  So they have the same chemical properties.
• Outline process of electrospray ionisation

  • The sample is dissolved in a volatile solvent
  • Then is injected with a fine hypodermic needles to create an aerosol
  • The end of the needle is attached to a high voltage power supply
  • Producing an xH+ ion
• Outline the process of electron impact ionisation

  • The sample is vaporised
  • Then the electron gun knocks of one electron from the molecule
  • Forming a X+ ion and an electron
• Define the first ionisation energy

  The amount of energy required to remove one mole of electrons from one mole of gaseplus atoms to form one mole of gaseous 1+ ions
• 
  

  Describe how time of flight mass spectrometer works

  1. Ionisation - electrospray or electron impact
  2. Acceleration - the ions are accelerated so they all have the same kinetic
  3. Ion drift - all the ions move at the same kinetic energy (larger mass = slower velocity) (smaller mass = higher velocity)
  4. Detection
• How are the ions in mass spectroscopy detected and measured?

  Positive ions hit the negatively charged plate and pick up an electron. The movement of electrons causes a current which can then be measured.
• Time of flight Equation

  $t=$$d(² root)m/2KE$
• How do you calculate Ar

  Ar = (mass × abundance) + (mass × abundance) / total abundance
• Kinetic energy equation

  $Ke =$$1/2 mv²$
• Calculating velocity using Ke

  V = (² root) 2Ke/m
• What is the molecular ion peak?

  The last significant peak on the graph
• On a mass spectrum for electronic impact what are many smaller peaks together showing?

  Fragmentation
• On a mass spectra for electrospray Ionisation, what are smaller peaks due to?

  Isotopes (e.g. C¹³ or H²)
• Equation for the first Ionisation energy if Al

  Al(g) -> Al+(g) + e‐
• Equation for the second ionisation of Ca

  Ca+(g) -> Ca2+(g) + e‐
• Equation for the third Ionisation energy of Fe

  Fe2+(g) -> Fe3+(g) + e-
• From a series of Ionisation energies of an element, how would you find which group its in?

  Look for the large jump in Ionisation energies ( e.g 4 -> 5th means its in group 4)
• Name the 3 factors effecting Ionisation energies:

  • Distance from nucleus
  • Nuclear charge
  • Shielding
• How does shielding effect the Ionisation energy?

  Attraction from the nucleus is shield by inner electrons

  More shells = more shielding = less energy needed to remove electrons
• How does nuclear charge effect Ionisation energies?

  • Greater nuclear charge = more protons (increased attraction between nucleus and outer e-)
  • So more attraction = more energy needed to remove
  • As e- are removed number of protons remains the same = greater nuclear charge
• How does distance from nucleus effect Ionisation energy?

  • Further away the outer e- from nucleus = less attraction between them
  • So less energy need to remove them
• Why is there a did in the transect of first ionisation energies of period 3 elements at aluminium?

  • The outer e- is in the 3p sub-shell, which is slightly further away from nucleus and has shielding from 3s, so takes slightly less energy to remove
• Why is there a did in the transect of first ionisation energies of period 3 elements at sulfur?

  • Two electrons are paired in the 3p orbital
  • So there's e- e- repulsion means it requires slightly less energy to remove it
• Why does the first ionisation energy decrease down the group?

  • Atoms get bigger, so electrons removed from higher energy level
  • The other e- is further from the nucleus
  • More shielding
  • Less attraction between e- and nucleus
  • Less energy need to remove the e-
• Why is there a big jump in ionisation energies?

  After all electrons have been removed from on sub-shell it moves to the next

  • Less shielded = stronger attration = more energy needed