electron structure

• number of electrons that fill first 4 subshells

  s - 2 electrons (1 orbital)

  p - 6 electrons (3 orbitals)

  d - 10 electrons (5 orbitals)

  f - 14 electrons (7 orbitals)
• atomic orbital

  region around nucleus that holds two electrons with opposite spins to minimise electron-electron repulsion

  
• s-orbital

  spherical shape

  from n=1 upwards, each shell contains one s orbital

  this gives a total of 1 x 2 = 2s electrons in each shell
• p orbital

  3D dumb-bell shape

  from n=2 upwards (from second shell), each shell contains 3 p-orbitals px, py, pz, at right angles to one another

  the x,y and z are used to describe the plane each orbital lies on

  3 x 2 = 6p electrons
• from n=3 upwards, each shell contains 5 d-orbitals

  5 x 2 = 10d electrons
• electrons fill the lowest energy orbitals first

  1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p

  the 4s subshell is filled before the 3d subshell because the 4s orbital has a lower energy than the 3d orbitals in neutral atoms

  
• electrons first occupy orbitals of equal energy singly before pairing up