Electron configuration

• Electron arrangement in atoms. 


  Electrons are found in energy levels [ shells ].

  Energy level with lowest energy closest to nucleus

  Electrons occupy lowest energy levels when in the ground state [ The ground state electron configuration is the arrangement of electrons around the nucleus of an atom with lower energy levels ] -> Aufbau principle.
• Electron configuration of Kr

  
  

  1s^2 2s^2 2p^6 3s^6 3p^6 3d^10 4s^2 4p^6
• Electron configurations of elements up to Kr.


  Electrons fill up om the same order for Kr except

  4s filled before 3d.
• Electron config. of cations


  Electrons removed in reverse order except 4s before 3d
• Atomic orbitals


  Max of 2 electrons with opposite spin

  Electrons represented as up and down arrows
• Filling atomic orbitals with the same energy - Hund's rule.

  The three p orbital: px, py, pz

  Empty orbitals filled first with electrons of the same spin - they're only paired after.
• Blocks in the periodic table.


  Block shows which sub-level highest energy electron(s) is found.

  
• First ionization energy.


  Energy required - Enthalpy Change - when 1 mol of electrons is removed from 1 mol of gaseous atoms
• First I.E equations

  M(g) -> M+ (g) + e-
• Second I.E equations


  M+ (g) -> M2+ (g) + e-
• Trend and explanation in 1st ionization energy down a group.


  Decrease.

  Outer electron is more shielded from attraction

  Atomic Radius increases
• Trend and explanation in 1st ionization across a period.


  General increase

  Increasing number of protons creates increasing nuclear attraction.

  Whilst outer electron in same prinicipal energy level and experiences shielding from nucleus
• Discontinuity between Gp 2 and Gp 3 elements. 


  Gp 3 outer electron easier to remove than Gp 2.

  Group 2 outer electron in 2s or 3s.

  Gp 3 outer elecentron is in a higher energy level [ 2p or 3p ] and experiences more shielding
• Discontinuity between group 5 and 6 elemrnts.

  Group 6 outer electrons easier to remove than Gp 5.

  Outer electrons in same sub-energy level [ 2p or 3 ]

  Group 6 electrons [ p4 ] is paired and mutual repulsion occurs.