Transcript Slide 1
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) 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- Color Change 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/gc sebitesize/img/gcsechem_14.gif • Chang, Raymond. Chemistry; McGraw-Hill: San Fransisco, 2007.