ionisation energy

• what is first ionisation energy 


  the energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form one mole of gaseous 1+ ions

  eg. X(g) > X+(g) + e-
• what is second ionisation energy 


  the energy required to remove 1 mole of electrons from one mole of gaseous +1 ions to form 1 mole of of gaseous 2+ ions

  eg X+(g) > X 2+(g) + e-
• why does it always take more energy to remove the second electron ?


  the second electron is removed from a positive ion, which has a higher proton to electron ratio, therefore there is a stronger attraction
• why is it harder to remove electrons in an new shell ?


  it is a new shell closer to the nucleus

  there is less inner shell shielding so stronger attraction to nucleus

  it is being moved from a positive ion with a higher proton to electron ratio
• what 3 factors effect the size of ionisation energy 


  distance from nucleus

  number of protons

  amount of inner shell shielding
• in a graph tracking number of electrons removed what does :

  • large increases signify
  • gradual increases signify 


  large increases signify as electrons are removed from a new shell closer to the cycles as it requires much more energy

  gradual increases signify electrons being removed within the same shell , it slowly increases as the P:E ratio increases
• what group of elements have a very high first ionisation energy

  noble gases, because they have a full outer shell so are very stable
• what is the trend in ionisation energy down a group and why 


  down a group first ionisation energy decreases because the outer electron is removed from an electron shell which is further from the nucleus, which therefore has more shielding, this leads to less attraction to the nucleus, this means the electron is easier to remove, which is why first ionisation energy is lower as you go down
• what is the trend in ionisation energy across a period and why 


  across a period first ionisation energy generally increases. this is because the number of protons increase, there is the small amount of shielding, nd the atomic radius decreases. these factors lead to the outer electron being more strongly attracted tot he nucleus so first ionisation energy increases across periods