1 / 79

Chapter 8

Chapter 8. Molecular Structure, Valence Bond Theory, and Hybridization. V alence S hell E lectron P air R epulsion Theory. Trigonal planar. Tetrahedral. Trigonal bipyramidal. Octahedral. VSEPR Theory. Explains how molecules obtain their shapes.

seilerl
Download Presentation

Chapter 8

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 8 Molecular Structure, Valence Bond Theory, and Hybridization

  2. ValenceShellElectronPairRepulsionTheory Trigonal planar Tetrahedral Trigonal bipyramidal Octahedral

  3. VSEPR Theory Explains how molecules obtain their shapes. Regions of High Electron Density (bonds or lone pairs) arrange themselves around a central atom as far away from each other as possible so as to minimize repulsive forces.

  4. From Chapter 8 Note Supplement • Molecular Shape: When explaining molecular shape include the following 3 steps in your answer: • What is the geometry of the molecule: based on the number of regions of high electron density. (See Table 8.1 pp. 215). • Discuss VSEPR theory: The regions of high electron density will get as far apart as possible from one another in order to minimize repulsive forces. (The underlined statement is an essential part of any explanation of molecular shape and is the essence of VSEPR theory). • What is the shape of the molecule: based on the number of bonds vs. unshared pairs. (See Table 8.2 pp. 216). • Explain placement of unshared pairs and/or bonds. (Easiest to use bond angles here).

  5. Table 8.1 page 215 Trigonal Planar

  6. Table 8.1 Page 215 The Number of Regions of High Electron Density around the Central Atom Determine Molecular Geometry.... 2 regions  linear (Bond angle = 180o) 3 regions  trigonal planar (Bond angle = 120o) 4 regions  tetrahedral (Bond angle = 109.5o) 5 regions  trigonal bipyramidal (Bond angles = 90o and 120o ) 6 regions  octahedral (Bond angle = 90o)

  7. Trigonal Bipyramidal Axial atoms are above and below the plane of the triangle on opposite sides of the molecule. Equatorial atoms are 120° apart and are within the plane of the triangle.

  8. Molecular Shape and VSEPR Theory Helps to Determine • Bond Angles • Molecular Polarity

  9. Table 8.1 page 215 Trigonal Planar

  10. Bond Angles • Bond angles are based on the geometry of the molecule • Slight adjustments may be necessary because of various space requirements for different types of regions of high electron density. • Lone pairs have the greatest space requirement followed by triple bonds then double bonds and finally single bonds which require the least amount of space around the central atom.

  11. Linear • Two atom molecule. • 2/0 central atom count. • Two atoms attached to the central atom and no lone pairs on the central atom. • Bond angle of 180°

  12. Linear Lewis Structure Molecular Geometry O = C = O

  13. Linear Lewis Structure Molecular Geometry O = C = O CO2 has two regions of high electron density resulting in a linear geometry. In order to minimize the repulsive forces the two oxygen atoms are bonded 180˚apart resulting in a linear shape.

  14. 3/0 or 2/1 count on central atom. • The geometry of the molecule is trigonal planar. • The base angle for this geometry is 120°. • The shape can be either trigonal planar or angular.

  15. Trigonal Planar

  16. Trigonal Planar BF3 has three regions of high electron density resulting in a trigonal planar geometry. In order to minimize the repulsive forces the three fluorine atoms are bonded 120° apart resulting in a trigonal planar shape.

  17. Explain why NO2- has a bond angle of 115.4°?

  18. NO2- has three regions of high electron density which results in a trigonal planar geometry and a base angle of 120°. However the greater space requirement of the unshared pair repels the bonds and results in a bond angle of 115.4°.

  19. 4/0 or 3/1 or 2/2 count on central atom. • The geometry of the molecule is tetrahedral. • The base angle for this geometry is 109.5°. • The shapes can be either tetrahedral, trigonal pyramidal, or angular.

  20. Why does water have a bond angle of 105°?

  21. Why does water have a bond angle of 105°? • The four regions of high electron density surrounding the oxygen tend to arrange themselves as far from each other as possible in order to minimize repulsive forces. This results in a tetrahedral geometry in which the H-O-H bond angle would be 109.5°. However, the two lone pairs around the oxygen atom, have a greater space requirement, effectively pushing the two hydrogen atoms closer together. The result is a H—O—H angle of 105°.

  22. 5/0 or 4/1 or 3/2 or 2/3 count on central atom. • The geometry of the molecule is trigonal bipyramidal. • The base angles for this geometry are 120° and 90°. However be careful with the angles on this geometry as they can vary depending upon the shape. • The shapes can be either trigonal bipyramidal, seesaw, • T- shaped, or linear.

  23. It will be helpful when explaining shapes based on a Trigonal Bipyramidal geometry to remember the difference between axial and equatorial. Axial atoms are above and below the plane of the triangle on opposite sides of the molecule. Equatorial atoms are 120° apart and are within the plane of the triangle.

  24. a

  25. a

  26. a

  27. I3- I3- I3- a

  28. 6/0 or 5/1 or 4/2 count on central atom. • The geometry of the molecule is octahedral. • The base angles for this geometry 90°. • The shapes can be either octahedral, square pyramidal, or square planar.

  29. a

  30. a

  31. Xenon Tetrafluoride Octahedral Geometry Square Planar Shape

  32. Explain the shape of IBr3 • Draw Lewis Structure • State VSEPR Theory (MRF) and Geometry • Place the Lone Pairs • Place the Bonds • State the Shape

  33. Explain the shape of Xenon Tetrafluoride

  34. Molecular Polarity • A dipole is anything with a positive end and a negative end. Another word for dipole is polar. • A bond is a dipole (polar) if it connects different atoms. • A polar molecule (dipole) is a molecule where the polar bonds are asymmetrically (not symmetrically) arranged (the dipoles do not cancel). • A nonpolar molecule is a molecule with no polar bonds or a molecule where the polar bonds are symmetrically arranged (the dipoles cancel).

  35. + - H Cl Dipole Moment • The dipole moment is the measurement of a molecules polarity. • Arrow points toward the more electronegative atom.

  36. O net dipole moment H2O H H Determining Molecular Polarity • Polar Molecule • Dipoles (Polar Bonds) are asymmetrically arranged and don’t cancel in this bent (angular) molecule.

  37. H net dipole moment CHCl3 Cl Cl Cl Determining Molecular Polarity • Therefore, polar molecules have... • asymmetrical charge distribution resulting in a positive and negative end to the molecule and a net dipole moment. • the dipoles don’t cancel

  38. F BF3 B F F Determining Molecular Polarity • Nonpolar Molecules • Dipoles (Polar Bonds) are symmetrically arranged and cancel out in this trigonal planar shaped molecule.

  39. Hybridization – The Methane Dilemma Carbon 1s22s22p2

  40. Fig. 10.7

  41. Fig. 10.8

  42. Orbital Hybridization Hybridization takes a certain number of different atomic orbitals and mixes (hybridizes) them to create an equal number of equivalent hybrid orbitals. • ONLY the CENTRAL ATOM(s) hybridize. 2. The number of regions of high electron density must equal the number of orbitals that hybridize.

  43. Atomic orbitals hybridization # hybrid of orbitals # of regions of HED

  44. # of regions of HED Atomic orbitals hybridization # hybrid of orbitals

More Related