Transition Metal Chemistry:Crystal Field Theory

Jessica ComstockKata HaeberlinKelsey Fisher

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/gcsechem_14.gif

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)

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)

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).

Crystal Field Theory• Developed in the 1930’s 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

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

Spectrochemical Series

• Energy difference ∆ depends on• Ligands• Geometry of the complex

I− < Br− < S2− < SCN− < Cl− < NO3− < N3− < F− < OH− < C2O42− < H2O < NCS− < CH3CN < py < NH3 < en < phen < NO2− < PPh3 < CN− < CO

High / Low Spin

• Low Spin• Large ∆• Strong-Field Ligand• Cn-, Co

• High Spin• Small∆• Weak-Field Ligand• I-, Br-

ColorChange in energy is

equal to energy of the absorbed photon

Energy of absorbed photon is opposite of the color observed

References

• http://www.bbc.co.uk/schools/gcsebitesize/img/gcsechem_14.gif

• Chang, Raymond. Chemistry; McGraw-Hill: San Fransisco, 2007.