Periodicity

• Periodicity


  The repeating pattern of physical or chemical properties going across the periods
• Classification of elements


  • Elements are classified as s, p or d block, according to which orbitals the highest energy electrons are in
• Blocks of elements


  • s block
  • p block
  • d block
• Atomic radius


  Decreases from left to right across a period, because the increased number of protons create more positive charge attraction for electrons which are in the same shell with similar shielding
• 1st Ionisation Energy


  Generally increases across a period, due to increasing number of protons as the electrons are being added to the same shell
• Mg to Al


  Small drop in 1st ionisation energy, because Al's outer electron is slightly easier to remove as it is in the 3p subshell which is higher in energy than Mg's 3s subshell
• P to S


  Small drop in 1st ionisation energy, because the second electron in the 3p orbital of S experiences slight repulsion which makes it easier to remove
• Metallic bonding


  • Strong bonding, gets stronger the more electrons there are in the outer shell that are released to the sea of electrons. A smaller sized ion with a greater positive charge also makes the bonding stronger. Higher energy is needed to break bonds.
• Macromolecular


  • Many strong covalent bonds between atoms, high energy needed to break covalent bonds– very high melting and boiling points
• Simple molecular


  • Weak van der Waals forces between molecules, so little energy is needed to break them – low melting and boiling points
• S8 vs P4


  S8 has a higher melting point than P4 because it has more electrons, so has stronger van der Waals forces between molecules
• Ar is monoatomic with weak van der Waals forces between atoms
• The same trends in atomic radius, ionisation energy, and melting/boiling points are observed in period 2 (Li, Be, B, C, N, O, F, Ne) as in period 3 (Na, Mg, Al, Si, P, S, Cl, Ar)