advanced inorganic chemistry chapter1

Upload: dung-doan

Post on 31-Oct-2015

115 views

Category:

Documents


0 download

DESCRIPTION

inorganic chemistry

TRANSCRIPT

  • 1. Molecular Symmetry (Point Group) Read Cotton Ch 3 Symmetry Operation a movement of a molecule that leaves the molecule apparently unchanged (takes the molecule into an equivalent configuration). ex) rotation, inversion Symmetry Element a point, line, or plane with respect to which symmetry operations are performed. Point-group Symmetry Operations Symmetry operations that leave at least one point of the molecule unmoved. cf. space group ( + translational symmetry operations)

    Symmetry Element Symmetry Operation Symbol

    Identity E

    n-fold Rotation Axis Rotation by 2/n (order: n) Cn

    Mirror Plane Reflection

    Center of Inversion Inversion i

    n-fold Axis of Improper Rotation

    Rotation by 2/n followed by reflection to rot. axis Sn

  • Reflection,

    v, vertical; h, horizontal; d, dihedral

    *

  • Inversion, i

    i

    C2

  • Rotation, Cn

    or C31 or C31

    or C32

    In general, for a given Cn, n symmetry operations exist: Cn, Cn2,, Cnn-1, Cnn (= E)

  • Improper Rotation, Sn

    S2 = i

    S1 =

    However, no C4 , h ! S42 = C2

  • 1

    2 3

    4

    1

    2

    3

    4

    1

    2

    3

    4 4

    1

    2

    3

    90

    Reflection

    1,3, 5, 7, tetrafluorocyclotetratraene

  • Sym. operations: E, C31, C32, , , or E, 2C3, 3 Sym. operations: E, C2, ,

    Sym. elements: E, C3, , , Sym. elements: E, C2, ,

  • Point Group (1) Compile a list of symmetry elements. (2) Compare it with the list that is characteristic of each point group.

    N2 CO C60 SF6 CCl4 NH3 XeF4 SiBrClFI

  • Sym. op: E, C31, C32, , , or E, 2C3, 3

    Sym. op: E, C2, ,

  • 1 2 3 4 5 6 7 8 9 10 11 12 13