Topic 8: Crystal Field Theory Part 1 Flashcards
Trend of lattice energies (-U) Ca to Zn
Decrease apart from Mn and Zn
Trend of hydration energies Ca to Zn
Decrease apart from Mn and Zn
Crystal Field Theory
A very simple ionic model which rationalises colour and magnetism (an electrostatic model)
Molecular Orbital Theory
A more complex, comprehensive bonding theory. Allows consideration of both covalent and ionic contributions
Name the 5 d-orbitals
dxy dxz dyz (lobes point between axis)
dx^2-y^2 dz^2 (lobes point along axis)
The underlying principle of Crystal Field Theory is …
The metal is treated as a positive point charge (M^+) and the ligands as negative point charges (:L^-) which donates an electron pair
The 5 d-orbitals are … so have the … energy in the M^+
The spherical field of negative charge alters this by …
degenerate
same
repulsion of electrons in d-orbitals, causing them to increase in energy
Effect of d-orbitals in octahedral fields
eg: dx^2-y^2 dz^2 increases in energy by 3/5 Delta O relative to barycentre (destabilised), direct overlap with axis
t2g: dxy dxz dyz deceases in energy by 2/5 Delta O relative to barycentre (stabilised), no direct overlap with axis
barycentre
Centre of gravity for splitting of d-orbitals
0 reference point (energy in spherical field)
Difference in 2 sets of d-orbitals
Delta O in octahedral
Delta T in tetrahedral
Effect of d-orbitals in tetrahedral fields
t2: dxy dxz dyz increases in energy by 2/5 Delta T relative to barycentre (destabilised), orbitals interact more strongly with ligands
e: dx^2-y^2 dz^2 deceases in energy by 3/5 Delta T relative to barycentre (stabilised), orbitals interact less strongly with ligands
delta O is always … than delta T because ..
much larger
6 ligands rather than 4 so more stabilisation and destabilisation
In delta O, ligands point directly at orbitals, don’t in delta T
Octahedral complexes can be … when … or …
Tetrahedral complexes are always … because …
low spin
delta O > P
high spin
high spin
P always > delta T
How can we experimentally determine delta O?
Send an electron from t2g to eg and calculate how much energy is required (how much light is absorbed)
CFSE of delta O=
E = hc v bar x NA
