Valence Shell Electron Pair Repulsion (VSEPR) Theory

2. 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.

4. 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

5. Electron pairs assume orientations about an atom to minimize repulsions.

6. 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

7. question: predict the shape of CO2 HCN CH4, NH3SO2 PCl5, SF6 and H2O by using VSEPR theory.

8. question: predict the shape of CO2 HCN CH4, NH3SO2 PCl5, SF6 and H2O by using VSEPRtheory.

9. 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

18. Valence bond theory The covalent bonds are formed by overlap of atomic orbitals each of which contains one electron of opposite spin.

19. 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.

21. Bonding in Methane

23. question : find the hybridazation type and geometry of CH4, PCl5, SF6. NH3 BeF2

24. Multiple Covalent Bonds

25. 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.

26. Combining Atomic Orbitals

28. No. e- in bonding MOs - No. e- in antibonding MOs Bond Order = 2

37. 12-7 Bonding in Metals • Electron sea model

38. Bonding in Metals Band theory.

39. Band Theory

40. Semiconductors

41. Photovoltaic Cells