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Transition Metal Chemistry: Crystal Field Theory

Transition Metal Chemistry: Crystal Field Theory. Jessica Comstock Kata Haeberlin Kelsey 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).

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Transition Metal Chemistry: Crystal Field Theory

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  1. Transition Metal Chemistry:Crystal 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/gcsechem_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 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

  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− < Br− < S2− < SCN− < Cl− < NO3− < N3− < F− < OH− < C2O42− < H2O < NCS− < CH3CN < py < NH3 < en < phen < NO2− < PPh3 < CN− < 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/gcsechem_14.gif • Chang, Raymond. Chemistry; McGraw-Hill: San Fransisco, 2007.

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