1.1 Atomic Structure

• evolution of atomic structure

  1. Solid sphere - dalton

  • atoms invisible

  2. Plum pudding model - jj thompson

  • discovered electrons
  • ball of +ve charge with -ve particles embedded in it

  3. Nuclear model - rutherford

  • dissaproved plum
  • +ve charge in the centre - nucleus

  4. Atomic model - bohr

  • discovered electron shells
  • electrons orbit the nucleus on shells

  neutrons - chadwick
• atomic mass


  avg mass of an atom of an element where an atom of C12 is exactly 12
• molecular mass


  avg. mass of a molecule where an atom of c12 is exactly 12
• isotopes


  diff no of neutrons but same number of protons
• mass spec - determines mass to identify substance

  1. ionisation - +ve ions

  sample vapourised

  • electrospray; high voltage charged over - each particle gains a H+ -> +ve charge
  • electron impact / electron gun; gun fires e- -> lose e- -> +ve charge

  2. acceleration

  • ions accelerated by electric field
  • lighter ions travel faster

  3. ion drift

  • no electric field - ions travel at the same speed
  • lighter ions drift speed

  4. detection

  • +ve ions hit -ve detector - gain e-, creating electric current
• when ionising transition metals, electron is lost from 4s before 3d
• ionisation energy


  amount of energy required to remove 1 mole of electrons from 1 mole of atoms in a gaseous state
• why is the 2nd IE higher than the 1st?

  electrons removed from a +ve atom where attraction has increases, requiring more energy
• shielding


  lessening of the pull of nucleus by inner shells of e-s

  • inner e-s repel outer -- lowers nucleus +ve charge on e-s
• trends in IE


  down; decreases

  across; increases
• effects on IE

  • nuclear charge; incraeses , IE increases -- bigger, stronger attraction
  • distance from nucleus; further from nucleus - more shells and shielding - less attraction -> easier to remove e-s
  • shielding; increases -- less effect of +ve charge - easier to remove