Periodicity

• Periodicity definition

  Trends in element properties with increasing atomic number
• Trend of atomic radius across period

  Atomic radius decrease across period, same shielding but more protons
• Trend of atomic radius down a group

  increase, atom becomes larger, more shielding
• Ionisation energy definition

  energy required to remove 1 mole of electrons from 1 mole of of gaseous atoms
• Ionisation energy across period trend

  increases, same shielding but more protons
• Deviation in ionisation energy trend across in from Mg to Al

  Al is in higher energy level, in 3p subshell, electron is further away so more easily lost
• Deviation in ionisation energy trend across in from N-O and P-S

  electron pair causes repulsion
• Why does argon have the highest IE in period 3?

  largest number of protons but same shielding. Single atom with electrons closer to nucleus, cannot be easily polarised