Ionisation Energies

• What is the first ionisation energy?


  The energy required needed to remove one mole of electrons from 1 mole of atoms in their gaseous state to form one more of 1+ ions.
• What is an equation to represent the first ionisation energy?


  $Li - Li^2 +$$e^-$
• What is the second ionisation energy?

  The energy needed to remove one mole of electrons from one mole of its ions in their gaseous state to form one mole of 2+ ions.
• What is the second ionisation of Lithium?


  $Li^+$$- Li^2 +$$e^-$
• What are the electrons attracted to?


  The positive protons in the nucleus.
• How does the atomic radius of an element affect the ionisation energy?


  As the atomic radius increases, the force of attraction between the outer. electron and the positive nucleus decreases.
• How does the nuclear charge of an element affect the ionisation energy?


  The greater the number of protons, the greater the force of attraction between the outer electrons and the nucleus.
• How does the effect of shielding affect the ionisation energy?


  Electrons are repelled by the inner shell electrons shells, this reduces the attraction between the outer electrons and the nucleus.
• What happens to the first ionisation energy as you go down a group?


  The first ionisation energy increases.
• What happens to the atomic radius as you go down a group?


  It increases as the outer electrons are further away from the nucleus.
• What happens to the effect of shielding as you go down a group?


  It increases as the number internal shells increases, so the effect of shielding is increased between the nucleus and the outer electron shell.
• What happens to the ionisation energy as you go across a period?


  It increases.
• What happens to the nuclear charge as you go across a period?

  It increases as the number of protons increases, so the attraction increases between the nucleus and the electrons.
• What happens to the atomic radius as you go across a period?


  It decreases as the electrons are more attracted to the nucleus.
• Why are successive ionisation energies always larger?

  1. When the first electron is removed, a positive ion is formed.
  2. The ion increases the attraction on to the remaining electrons and so they energy required to remove the next ion is larger.
• What is periodicity?

  A repeating pattern across a period.
• Why has helium the largest first ionisation energy?

  It first electron is in the first shell closest to the nucleus and has no shielding effects from inner shells. It has a bigger ionisation energy that H as it has one more proton.
• Why has Na a much lower first ionisation energy than Neon?

  Because Na will have its outer electron in a 3s sub shell further from the nucleus and is more shielded. So Na‘s outer electron is easier to remove and has a lower ionisation energy.
• Why is there a small drop from Mg to Al?

  Al is starting to fill up a 3p sub shell, whereas Mg has its outer electron in the 3s sub shell. The electrons in the 3p subshell are slightly easier to remove because the 3p electrons are higher in energy and are also slightly shielded by the 3s sub shell.
• Why is there a small drop from P to S?

  With sulphur there are 4 electrons in the 3p sub shell and this starting to fill the 3p orbital.When the second electron is added to a 3p orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.