Periodicity

• Periodic table:

  • Recent changes have now altered the numbering of the groups in the periodic table from 8 to 18:
  • Groups 1-2 remain the same
  • The transition metal numbers groups 3-12
  • Group 3-8 are now 13-18
• Blocks:

  • S block —> group 1-2
  • P block —> groups 13-18
  • D block —> groups 3-12 (transition metals)
  • The lanthanides & actinides have electrons in the F orbitals so are found in the F-block
• Periodicity —> Repeating patterns seen within groups & periods
• Ionisation energy:

  • The energy required to:-
  • remove on electron from the ground state of each atom
  • In a mole of gaseous atoms of that element.
  • 1st ionisation energy: X(g) —> X+(g) + e-
  • 2nd ionisation energy: X+(g) —> X2+(g) +e-
  • only remove one electron at a time
  • As you go down a group the 1st ionisation energy decreases
  • As you go across the group the 1st ionisation energy increases, but there are decreases due to the subshell
• Ionisation energy factors:

  • Atomic radius : The larger the radius the further away the outer electron is from the nucleus, so easier to lose, lowering ionisation energy.
  • Nuclear charge: more protons increase the pull on the outer electron increasing ionisation energy
  • Electron shielding : more inner shells increases the repulsion of the outer electron, lowering ionisation energy
• Periods:

  • Across a period ionisation energy increases as the atomic radius decreases and nuclear charge increases, but the electron shielding stays fairly constant across the period
  • However slight decrease after group 2 and 15 elements occur due to them have filled and half-filled subshells
  • Filed or half-filled subshells are energetically stable, so require more energy to remove an electron
• Groups:

  • Down a group ionisation energy decreases despite the increase in nuclear charge from the additional protons as:
  • The atomic radius increases down the group making the outer electron easier to lose
  • The electron shielding is greater due to the increase in shells so repulsion of the outer electron increases.
  • The atomic radius and electron shielding outweigh the attraction due to the nuclear charge
• Metallic bonding —> Metal atoms held together as giant lattice of positive ions (cations) surrounded by mobile delocalised electrons.

  • Delocalised electrons are bonding electrons not fixed between two atoms but are mobile and shared by many atoms
• Metallic bond —> An electrostatic attraction between the positive metal ions and the delocalised electrons
• Metallic properties:

  • the presence of delocalised electrons allow for electrical conductivity as they can carry charge
  • As the electrostatic attraction between delocalised electrons and cations is strong and non-directional, large amounts of energy is needed to break it, thus giving metals high melting points
• Giant covalent lattice:

  • Carbon and silicon are able to form multiple covalent bonds and create huge repeating lattices
  • Silicon and carbon (as diamond) form 3D structures but carbon (as graphite) form 2D sheets of hexagons.
  • graphene is a single sheet of graphite
• Giant covalent properties:

  • High melting points —> strong covalent bonds need a large amount of energy to disrupt lattice structure
  • graphite and graphene both have delocalised electrons and so are good conductors of electricity