Transition Metal Chemistry: Crystal Field Theory

1
Transition Metal ChemistryCrystal Field Theory

• Jessica Comstock
• Kata Haeberlin
• Kelsey Fisher

2
Transition Metals

• elements in which the d and f subshells are
  progressively filled
• 50 elements
• transition elements with incomplete d subshells
  tend to form complex ions (Chang 935)

http//www.bbc.co.uk/schools/gcsebitesize/img/gcse
chem_14.gif
3
Periodic Trends

• Going across a period, the valence doesn't
  change.
• As a result, the electron being added to an atom
  goes to the inner shell, not outer shell,
  strengthening the shield.
• Why are they called transition metals ?
• The elements represent the successive addition of
  electrons to the d orbitals of the atoms.
  Transition metals represent the transition
  between group 2 and 13 elements.
• (Wikipedia)

4
Properties

• high tensile strength
• high density
• high melting and boiling points
• often form colored compounds
• solid at room temperature (except mercury)
• form complex ions
• often paramagnetic
• (Wikipedia)

5
Oxidation States

• Unlike group 1 and group 2 metals, transition
  element ions can have multiple stable oxidation
  states.
• They can lose d electrons without a high
  energetic penalty (Wikipedia).

6
Crystal Field Theory

• Developed in the 1930s by Hans Bethe and John
  Hasbrouck van Vleck
• Model that describes electronic structure of
  transition metal compounds
• Accounts for
• Some Magnetic Properties
• Colors
• Hydration Enthalpies
• Spinal Structure of Transition Metals

7
Splitting

• Attraction between positively charged metal
  cation and negatively charged electrons of the
  ligand
• Repulsion of electrons
• Splitting affected by
• Nature of metal ion
• Oxidation State
• Arrangement of ligands around the metal ion
• Nature of the ligands

8
Spectrochemical Series

• Energy difference ? depends on
• Ligands
• Geometry of the complex
• I- lt Br- lt S2- lt SCN- lt Cl- lt NO3- lt N3- lt F- lt
  OH- lt C2O42- lt H2O lt NCS- lt CH3CN lt py lt NH3 lt en
  lt phen lt NO2- lt PPh3 lt CN- lt CO

9
High / Low Spin

• Low Spin
• Large ?
• Strong-Field Ligand
• Cn-, Co
• High Spin
• Small?
• Weak-Field Ligand
• I-, Br-

10
Color

• Change in energy is equal to energy of the
  absorbed photon
• Energy of absorbed photon is opposite of the
  color observed

11
References

• http//www.bbc.co.uk/schools/gcsebitesize/img/gcse
  chem_14.gif
• Chang, Raymond. Chemistry McGraw-Hill San
  Fransisco, 2007.