1. Molecular Orbital Theory
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 Theory
Molecular Orbital 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, NH3 SO2 PCl5, SF6 and H2O by using VSEPR theory.

8. question: predict the shape of CO2 HCN CH4, NH3 SO2 PCl5, SF6 and H2O by using VSEPR theory.

9. lone pair -lone pair  lone pair e-bond pair  bond pair-bond pair
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

22. Valence Electron Pair Geometry
Number of Orbitals
Hybrid Orbitals
Linear 2 sp
Trigonal Planar 3
sp2
Tetrahedral 4
sp3
Trigonal Bipyramidal 5
sp3d
Octahedral 6
sp3d2

23. question : find the hybridazation type and geometry of CH4, PCl5, SF6
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. Bond Order =
No. e- in bonding MOs - No. e- in antibonding MOs 2

36. Bonding in Metals
Electron sea model
Band theory.

37. 12-7 Bonding in Metals
Electron sea model

38. Bonding in Metals
Band theory.

39. Band Theory

40. Semiconductors Intrinsic semiconductors: fixed band gap.
Ex. CdS, absorbs violet light and some blue, reflects less energetic light. Thus looks bright yellow.
GaAs, small band gap, all visible light is absorbed, looks black.
Extrinsic semiconductors: band gap is controlled by addition of impurities – doping.
Energy level of P is just below the conduction band of Si. P uses four of five electrons to bond to Si, one left over can be donated.
n-type semiconductor – n refers to negative, the type of charge that is MOBILE.
Energy level of Al is just above the valence band. Electrons can move into the Al orbital and leave a HOLE in the valence band. Positive charge can move around thus this is a p-type semiconductor.

41. Photovoltaic Cells