Presentation on theme: "Colour and the d block. UV / Vis frequencies are have photons with energies of the sort of values needed to promote electrons from their ground state."— Presentation transcript:
Colour and the d block
UV / Vis frequencies are have photons with energies of the sort of values needed to promote electrons from their ground state energy level to a higher level. A typical substance will require UV photons so does not absorb Visible light. Most substances are colourless.
d – block metal complexes These have unusually close energy levels due to the splitting of the 3d orbitals in a non spherical environment.
3d orbitals in gas Energy
But in an octahedral complex two of the orbitals will be closer to ligands than the other three. But ligands usually have a negative charge …..so electrons in the d orbitals are repelled. They have a higher energy
3d orbitals in complex Energy Further from ligands Closer to ligands
d electrons will tend to go preferentially into the lower energy orbitals further from the ligands. Ti has the electron configuration [Ar] 3d 2 4s 2 So Ti 3+ has the electron configuration [Ar] 3d 1
3d orbitals in Ti 3+ complex Energy
3d orbitals in Ti 3+ complex Energy Absorbs a photon of yellow light
So what d block complexes will not be coloured ? Ones with no d electrons eg…… Sc 3+, Ti 4+..or those for which the d shell is full so electrons cannot move. Eg… Zn 2+, Cu +
3d orbitals in Cu + complex Energy
Different ligands cause different degrees of splitting of the d orbital energies. Ligand exchange therefore usually causes a change of colour
3d orbitals in Ni 2+ complexes Absorbs red appears green Absorbs orange appears blue Ni(H 2 O) 6 2+ Ni(NH 3 ) 6 2+