Valence Shell Electron Pair Repulsion (VSEPR) Theory by 6t0SpFkz

VIEWS: 82 PAGES: 44

									                        Molecular Geometry
Molecules of different subtances have diverse shapes. Atoms attach to one another
 in various geometric arrangements. The overall molecular shape of a molecule is
 determined by its bond angles in three dimensions. The shape of a molecule is very
 important for its physical and chemical properties. Molekül geometrisini açıklamak
 için farklı kuramlar mevcuttur. modeller


    VSEPR                  Valence Bond                 Molecular Orbital
                               Theory                        Theory
     Valence Shell Electron Pair Repulsion
                   (VSEPR) Theory



It is a method for predicting the shape of a molecule from the
knowledge of the groups of electrons around a central atom.
   Electron pairs (bonding and nonbonding electrons) repel one
   another, as a result , the electron pairs remain as far apart as
   possible from another as possible to minimize the repulsion.



   •   Two electron pairs in the valence orbital are arranged linearly
   •   Three electron pairs are organized in a trigonal planar arrangement
   •   Four electron pairs are organized in a tetrahedral arrangement
   •   Five electron pairs are arranged in a trigonal bipyramid
   •   Six electron pairs are organized in an octahedral arrangement



The repulsion of lone pair electrons is grater than the repulsion of bond pair electrons
Electron pairs assume orientations about an atom to minimize repulsions.
             Applying the VSEPR theory.
• draw a plausible Lewis structure of the molecule or polyatomic
  ion.
• Determine the number of unshared electron pairs and numbers
  of bonds around the central atom ( multiple bonds count as a
  single bond)
• B + No
• Establish the geometrical orientation of the electron pairs
  around the central atom as linear, trigonal planar, tetrahedral,,
  trigonal bipyramid or octahedral
• Describe the molecular geometry
question: predict the shape of CO2 HCN CH4, NH3 SO2 PCl5,
SF6 and H2O by using VSEPR theory.
question: predict the shape of CO2 HCN CH4, NH3 SO2 PCl5,
SF6 and H2O by using VSEPR theory.
The nonbonding electron pairs are as important as bonding electron pairs in
   determining the structure.

Nonbonding electrons take up more space in the valence shell than the bonding
  electrons.

If one or more of the electron pairs are lone pairs, the distribution of electron
    pair and the geometrical shape of the molecule must be different.

The bond angles decrease as the number of nonbonding electron pairs
   increases

                             Repulsion strengths

    lone pair -lone pair  lone pair e-bond pair  bond pair-bond pair
                    Valence bond theory
The covalent bonds are formed by overlap of atomic orbitals each of which
   contains one electron of opposite spin.
The valence bond method predicts molecule shapes from the shapes and
orientation of the atomic orbitals and their overlap regions when two atoms
approach.

 In most cases the orbitals that overlap are reconfigured orbitals, called hybrid
orbitals, having different shapes and orientations than pure orbitals.

The process of hybridization corresponds to a mathematical mixing of the valence-
shell atomic orbitals.
Bonding in Methane
   Valence Electron Pair   Number of   Hybrid
        Geometry            Orbitals   Orbitals
Linear                        2          sp
Trigonal Planar               3          sp2
Tetrahedral                   4          sp3
Trigonal Bipyramidal          5         sp3d
Octahedral                    6         sp3d2
question : find the hybridazation type and geometry of
  CH4, PCl5, SF6. NH3 BeF2
Multiple Covalent Bonds
            Molecular Orbital Theory
A molecular orbital describes a region of space in a molecule where
electrons are most likely to be found.

Molecular orbitals are formed by combining atomic orbitals on different
atoms.
Combining Atomic Orbitals
               No. e- in bonding MOs - No. e- in antibonding MOs
Bond Order =
                                    2
             Bonding in Metals

Electron sea model          Band theory.
   12-7 Bonding in Metals

• Electron sea
  model
         Bonding in Metals
Band theory.
Band Theory
Semiconductors
Photovoltaic Cells

								
To top