electronic structure

• Bohr model


  Early model of the atom with electrons in spherical orbits
• Early models of atomic structure predicted that atoms and ions with noble gas electron arrangements should be stable
• Electrons in the A-level model


  • Arranged on principle energy levels numbered 1,2,3,4...
  • Arranged on sub energy levels labelled s, p, d and f
  • s holds up to 2 electrons
  • p holds up to 6 electrons
  • d holds up to 10 electrons
  • f holds up to 14 electrons
• Filling up sub levels


  Fill each orbital singly before starting to pair up the electrons
• Orbitals


  Represent the mathematical probabilities of finding an electron at any point within certain spatial distributions around the nucleus
• Shapes of orbitals


  • Each orbital has its own approximate, three dimensional shape
  • It is not possible to draw the shape of orbitals precisely
• Principle energy levels


  • 1
  • 2
  • 3
  • 4
• Sub-levels


  • 1s
  • 2s, 2p
  • 3s, 3p, 3d
  • 4s, 4p, 4d, 4f
• The periodic table is split into blocks. A s block element is one whose outer electron is filling a s-sub shell
• Writing electronic structure using letters and numbers

  1. Number of main energy level

  2. Name of type of sub-level

  3. Number of electrons in sub-level
• For oxygen


  • 1s2 2s2 2p4
• For fluorine


  • Using spin diagrams: An arrow is one electron, the arrows going in the opposite direction represents the different spins of the electrons in the orbital, box represents one orbital
• When a positive ion is formed


  Electrons are lost
• When a negative ion is formed


  Electrons are gained
• For Mg


  • 1s2 2s2 2p6 3s2 but Mg2+ is 1s2 2s2 2p6
• For O


  • 1s2 2s2 2p4 but O2- is 1s2 2s2 2p6