evidence for electron shells

• ionisation occurs when atoms lose or gain electrons

  Mixture of positive and negative ions is called a plasma
• ionisation energy

  • energy needed to remove one mole of electrons from one mole of atoms in their gaseous state to form one mole of 1+ ions (also gaseous)
• factors affecting ionisation energy

  • atomic radius, the larger the atomic radius, the smaller the nuclear attraction
  • nuclear charge, the higher the nuclear charge, the larger the attractive force experienced
  • electron shielding, the more inner shells , the larger the shielding effect as electrons are repelling in full shells
• succesive ionisation energy

  • as each electron is removed, there is less repulsion between the remaining electrons and each shell will be drawn in slightly closer to the nucleus
  • the positive nuclear charge will outweigh the negative charge every time an electron is removed
  • as the distance of each electron from the nucleus decreases slightly, the nuclear attraction increases. More energy is needed to remove each successive electron
• Evidence for shells 1

  • the Bohr model of the atom describes a positive nucleus, with negatively charged electrons orbiting round it in defined energy levels. Succesive ionisation energies support this.
  • Not all successive ionisation energies in an element increase regularly - there are jumps that tell jus a lot about the electron structure of a substance
• evidence for shells 2

  • when electrons are removed from outer shell , more electrons from other shells are removed if more ionisation occurs
  • this takes much more energy because of the smaller atomic radius, so a 'jump' is observed
  • by looking at where these jumps occur it's possible to deduce the electronic structure