Periodicity

• what is periodicity?

  periods showing repeating patters and trends in physical and chemical properties
• Periodic table structure

  -arranged by increasing proton number (left to right)

  -groups have similar chemical properties

  -down group= same number of outer electrons
• s block = group 1 and 2
• p block = group 3 to group 0
• d block = transition metals /elements
• energy of orbitals increase from s to f
• what is ionisation energy?

  energy required to remove one electron from each atom in one mole of a gaseous atom to form one mole of gaseous 1+ ions
• one electron is removed at a time for ionisation energies
• 10th ionisation energy of Na


  Na ⁹⁺ (g) —> Na ¹⁰⁺ (g) + e⁻
• successive ionisation energies

  occurs when further electrons are removed

  • requires more energy
  • increased electrostatic force of attraction between nucleus and electron
• factors that affect ionisation energy

  1.) atomic radius

  2.) nuclear charge

  3.) electron shielding
• atomic radius

  the greater the distance between the nucleus and outer electron, the less nuclear attraction

  • the further , the lower the ionisation energy
• atomic radius

  down a group:

  • atomic radius increases
  • distance between electron and nucleus increases so attraction decreases
  • increased shielding effect
  • ionisation energy decreases
• atomic radius

  across a period:

  • atomic radius decreases due to increased nuclear charge
  • despite having the same number of electron shells, outer electron gets pulled closer to nucleus
  • increased attraction
  • ionisation energy increases
• nuclear charge

  the more protons within a nucleus of an atom, the greater the attraction between the nucleus and outer electron

  • nuclear charge increases with increasing atomic number
• nuclear charge

  down the group:

  • increased number of protons
  • more energy required to overcome the force of attraction
  • increased ionisation energy
• Nuclear charge

  across a period:

  • increased number of protons
  • increased nuclear charge
  • more energy required to overcome the force of attraction
  • ionisation energy increases
• electron shielding

  inner shell electrons repel the outer shell electrons

  • reduces the attraction between the nucleus and the outer electrons
• electron shielding

  down a group:

  • increased number of shells
  • greater shielding
  • attraction is reduced
  • ionisation energy decreases
• electron shielding

  across a period:

  • same number of shells
  • similar shielding
  • no effect
• overall effect of factors on ionisation energy

  down the group, ionisation energy decreases:

  • atomic radius increases
  • nuclear charge increases
  • shielding increases

  atomic radius and shielding outweigh the effect of nuclear charge (nuclear attraction decreases)
• overall effect of factors on ionisation energy

  across a period, ionisation energy increases:

  • atomic radius decreases
  • nuclear charge increases
  • shielding has no effect

  nuclear attraction increases and so more energy is required to remove outer electron
• large jump between ionisation energies indicates the group (change in shell)
• decrease in first ionisation energy between Be and B

  4th electron in Be: 2s sub shell

  5th electron in B : 2p sub shell

  • further away from the nucleus
  • less nuclear attraction so electron is easier to remove

  B has a lower first ionisation energy than Be
• decrease in first ionisation energy between O and N

  O: paired electron in 2p sub shell

  • repel each other due to having opposite spins
  • electron is removed more easily

  paired electron and opposite spins is more destabilising in comparison to the configuration of nitrogen (no paired electron in 2p sub shell)
• Trend in ionisation energies