Atomic Structure

Atomic Structure

1. Fundamental Particles

   • Atoms
     • protons
     • neutrons
     • Electrons
   • Isotopes
     • SAME NUMBER OF PROTONS DIFFERENT NUMBER OF NEUTRONS
   • Calculating relative atomic mass
     • multiply all the isotopes with their relative abundance and divide by the sum of total relative abundance (usually 100%)
     • relative atomic mass is the average mass of an atom of an element divided by one twelfth of the mass of an atom of carbon twelve

2. The Mass Spectrometer

   • the instrument is kept at a high vacuum so air particles don't interfere
   • vaporisation
     • the sample is vaporised and injected into the mass spectrometer
   • Ionisation
     • an electron gun is fired at the sample to knock an electron off the atoms making them positive. sometimes two are knocked off so they have a +2 charge
   • Acceleration
     • an electric field is produced using two negativley charged plates with central slits. the ions accelerate towards the plates and are squeezed through the slits into a beam
   • Deflection
     • the accelerated ions hit a magnetic field at right angles with it's direction of travel. the beam is deflected in the arc of a circle. the deflection depends on the mass over charge ratio. heavy ions are deflected much less than light ions. doubly charged ions are deflected twice as much. the stronger the magnetic field the greater the deflection
   • Detection
     • the field is gradually increased so ions of increasing masses hit the detector plate. the ions accept an electron and induce a charge- the number of ions that strike the plate and induce a current which is proportional to their abundance. the computer can use the strength of the magnetic field to work out the original mass over charge and produce a mass spectrum
   • doubly charged ions behave as if they have half the mass of the singly charged counterpart

3. Detail electron arangment

   • It is impossible to know exactly where an electron is or where it is going
   • We can plot where an electron is most likely to be found
   • These are called atomic orbitals-each one can hold 2 electrons
   • Electrons are arranged into energy levels(shells 1,2,3 etc.)
   • There are sub levels called S, P, D and F
     • each shell can hold a specific number of these sub levels
       • e.g. shell 1 can just hold one "s" orbital shell 2 can hold one s orbital (2s) and 3 P orbitals (2px, 2py and 2pz aka 2p^6) etc.

4. ionisation energies

   • Factors affecting Ionisation energy
     • Atomic Radius (distance)
     • Nuclear Charge
     • Electron Sheilding
   • 1st ionisation energy of an element is the energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1 plus ions