1.5 - Evidence for Electronic Structure of Atoms

• ionisation energy

  measure of the energy required to completely remove an electron from an atom of an element in the gaseous form
• ionisation energy units

  kJ mol^-1
• first ionisation energy

  energy required to remove 1 mole of electrons from each atom in 1 mole of gaseous atoms to form +1 ions
• second ionisation energy

  energy required to remove 1 mole of electrons from each ions in 1 mole of gaseous +1 ions to form +2 ions

  (other successive ionisation energies follow the same pattern)
• ionisation energies - endothermic or exothermic

  endothermic as energy is taken in by reaction
• factors affecting ionisation energy

  nuclear charge

  electron shell

  shielding
• how nuclear charge affects ionisation energies

  the more protons the stronger the positive charge of the nucleus so the stronger the attraction between nucleus and electrons
• how electron shells affect ionisation energies

  the more shells the further away from the nucleus electrons are so are less attracted to it
• how shielding affects ionisation energies

  the more electrons between nucleus and outer electron the less it is attracted to the nucleus
• how successive ionisation energies for an element change

  they get bigger and bigger because:

  electron gets closer to the nucleus

  it's more difficult to remove electrons from an increasingly positive ion as there's less repulsion between remaining electrons
• big jumps in graphs for successive ionisation energies

  mean there's a new shell broken into
• why logorithms are used in graphs for successive ionisation energies

  makes values fit on the vertical axis while showing big jumps in value
• uses of successive ionisation energies graphs

  predict electronic structure of elements

  find group element is in

  provide evidence to support theory that electrons are arranged in shells
• how can paired electrons be stable and why


  if they have opposite spins so magnetic force of attraction from opposite spins counteracts electrical repulsion from negative charges
• electrons and energy

  when electrons take in energy they become excited and move to higher energy levels

  when electrons release energy they move to a lower energy level and release light
• emission spectrum/line spectrum

  shows frequencies of light emitted when electrons move back down an energy level which appear as coloured lines on a dark background
• why emission spectrum for each element is different

  each element has a different electron arrangement so frequencies of radiation absorbed/emitted are different
• lines in emission spectra

  they get closer together as frequency increases

  they converge because energy levels get closer together as frequency increases
• 4 basic principles of electron shells

  electrons only exist in shells

  each shell has a fixed enegy

  when electrons move between shells EM radiation is absorbed/emitted

  EM absorbed/emitted will have a fixed energy