1. Molecular Shape VSEPR Model

2. Molecular Shape Physical/Chemical PROPERTIES SHAPE of Molecule (VSEPR) Overlap of ORBITALS (Hybridization)

3. VSEPR Model VSEPR Model Lewis Structure used to determine the molecular geometry or shape. Lewis Structure used to determine the molecular geometry or shape. –Model used is called Valence Shell Electron Pair Repulsion model VSEPR – based on arrangement that minimizes the repulsion of shared and unshared pairs of electrons around the central atom. VSEPR – based on arrangement that minimizes the repulsion of shared and unshared pairs of electrons around the central atom.

4. Predicting Shapes Start with Lewis Dot structure Start with Lewis Dot structure –Show both bonding/nonbonding pairs e- –Note that double and triple bonds are viewed as single bonds of e - density.

5. Predicting Shapes 2 pairs e - LINEAR 2 pairs e - LINEAR 3 pairs e - TRIGONAL PLANAR 3 pairs e - TRIGONAL PLANAR 4 pairs e - TETRAHEDRAL 4 pairs e - TETRAHEDRAL 5 pairs e - TRIGONAL BIPYRAMIDAL 5 pairs e - TRIGONAL BIPYRAMIDAL 6 pairs e - OCTAHEDRAL 6 pairs e - OCTAHEDRAL Comparisons http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/VSEPR.swf

6. Molecular Shapes (routine) Draw Lewis Structure Draw Lewis Structure –Focus on central atom Count up the regions of electron density on central atom Count up the regions of electron density on central atom –i.e., bonding and nonbonding pairs Count up the number of atoms bonded to the central atom Count up the number of atoms bonded to the central atom

7. Assign Numbers… electron density, atoms bonded Molecule Shape Bond Angle CO 2 2,2 linear 180 o CO 2 2,2 linear 180 o CH 4 4,4 tetrahedral 109 o CH 4 4,4 tetrahedral 109 o NH 3 4,3 pyramid 107 o NH 3 4,3 pyramid 107 o H 2 O 4,2 bent 105 o H 2 O 4,2 bent 105 o

8. Molecular Geometry Examples Examples Examples http://www.uwosh.edu/faculty_staff/xie/tutorial/vsepr.htm#live

9. Hybridization Mixing of two or more atomic orbitals of similar energies on the same atom to give new orbitals or equal energies. Mixing of two or more atomic orbitals of similar energies on the same atom to give new orbitals or equal energies. –Special types of atomic orbitals that have energy intermediate between s and p orbitals. Animation http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/hybrv18.swf More… http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/bom5s2_6.swf

10. sp 3 Hybridizaiton

11. Energy of sp 3 Orbitals The 2s electron is promoted to the 2pz orbital and the four orbitals then undergo hybridization to form four degenerate orbitals. As these new orbital have emerged from one s and three p orbitals they are called 'sp3' orbitals.

12. Ammonia bonding electrons in a probability area for the hybrid orbital...

13. Geometry of Hybrid Orbitals Atomic Orbitals Type of Hybrid Number of Hybrid Geometry s, p s, psp2 (e - pairs) Linear s, p, p sp 2 3 (e - pairs) Trigonal Planar s, p, p, p sp 3 4 (e - pairs) Tetrahedral

14. Molecular Orbitals Sigma Bonds (  ) Sigma Bonds (  ) –Two atomic orbitals combine to form a molecular orbital that is symmetricl around the axis connecting nuclei.

15. Sigma Bonds

16. Molecular Orbitals Pi Bonds (  ) Pi Bonds (  ) –Side-by-side overlap of two p atomic orbitals produces a pi-bonding molecular orbital. –Atomic orbitals overlap less than in sigma bonding so pi (  bonds tend to be weaker.

17. Hybridization and Multiple Bonds Maximum of two electrons per orbital Maximum of two electrons per orbital –So multiple bonds must include sigma (  ) and pi (  ) bonds. Double Bonds  One  and one  Double Bonds  One  and one  Triple Bonds  One  and two  Triple Bonds  One  and two 

18. Formation of Sigma and Pi molecular orbitals

19. Molecular Orbitals

20. Correlation Diagram