Electron Configurations

1
Electron Configurations

• Of
• Atoms Ions

2
Men their Rules

• Aufbau Principle Start at the beginning
  (Electrons enter lowest energy level 1st)
• Pauli Exclusion Principle Only 2 allowed
• (Only 2 electrons allowed in any orbital)
• Hunds Rule Stay solo as long as possible
• (For orbitals of equal energy, 1 electron
  enters each until all orbitals contain one before
  any pairs up.)

3
Consequences of Aufbau Principle

• Electrons enter orbitals in order of increasing
  energy levels.
• This order is shown in text on page 111.
• 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p
• 7s 5f 6d 7p
• But there are two exceptions, namely Cu Cr, who
  subtract 1 from 4s and add it to 3d.

4
Consequences of Pauli exclusion

• The s orbital is filled with 2 electrons.
• The 3 different orientations of the p orbital,
  px, py, pz, each contain a max of 2 electrons
• The 5 different orientations of d orbitals, dxy
• dxz, dyz, dx2-y2, dz2, can have max of 2
  each.
• The 7 different orientations of f orbitals also
  only have 2 electrons for each suborbital.

5
Consequences of Hunds Rule

• One electron is added to px, then 1 to py, then 1
  to pz, before the second one is added to px. The
  5th electron is then added to py, 6th to pz.
• The same pattern is observed for the d f
  suborbitals.
• NOTE The single electrons all have parallel
  spins. When the 2nd electron is added to each
  suborbital, it spins in the opposite direction.

6
Relating this to the periodic table

• The s block Groups IA IIA
• The p block Groups IIIB VIII (13-18)
• The d block Transition elements (Groups
  IIIA-IIB Groups 3-12)
• The f block Rare earth metals

7
What this means

• You merely need to follow the periodic table to
  figure out electron configurations.
• The block (s, p, d, f) indicates where the last
  electrons go.
• Follow the period numbers, 1-7, because these are
  your energy levels then remember suborbitals
  penetrate differently.
• d block starts at 3d f block starts at 4f

8
How can we apply this?

• Follow the periodic table numerically
• 1s2 (takes you to He) 2s2 (to Be) 2p6 (to Ne) 3s2
  (to Mg) 3p6 (to Ar) 4s2(to Ca) 3d1-3 (to V)
• Cr (1st exception) 1s22s22p63s23p64s13d5
• Cu (2nd exception) 1s22s22p63s23p64s13d10
• Mn 1s22s22p63s23p64s23d5
• Zn 1s22s22p63s23p64s23d10
• Ga 1s22s22p63s23p64s23d104px1

9
Applications, continued

• La is beginning of the lanthanide series
• 1s22s22p63s23p64s23d104p65s24d105p66s25d1
• The pattern slightly changes with Ce
• 1s22s22p63s23p64s23d104p65s24d105p66s25d14f 1
• Pr puts it back on track
• 1s22s22p63s23p64s23d104p65s24d105p66s24f 3
• This is because 4f and 5d are close in energies

10
Noble Gas Configurations

• Instead of writing entire core electron
  configuration of the noble gas, one can
  abbreviate it NG write only valence e-
• Al 1s22s22p63s23px1 or Ne3s23px1
• Ag1s22s22p63s23p64s23d104p65s24d9 or Kr5s24d9
• Am1s22s22p63s23p64s23d104p65s24d105p66s24f 14
  5d106p67s25f 7 or Rn 7s25f 7
• Sg Rn7s25f 146d4 862144 106 Sb atomic

11
Orbital Notations

• This shows all 4 quantum numbers
• n (principle quantum ) energy lvl 1,2,3...
• l (angular momentum Q.N.) shape s,p,d,f
• m (magnetic Q.N.) x, y, z for p, etc
• s (spin Q.N.) 1/2 (cw) or -1/2 (ccw) shown
  as upward or downward arrows
• 16 8O ___ ___ ___ ___
  ___
• 1s 2s 2px y z