1 / 23

Lecture 25: VSEPR

Lecture 25: VSEPR. Reading: Zumdahl 13.13 Outline Concept behind VSEPR Molecular geometries. VSEPR Background. • The Lewis Dot Structure approach provided some insight into molecular structure in terms of bonding, but what about geometry?.

edric
Download Presentation

Lecture 25: VSEPR

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. Lecture 25: VSEPR • Reading: Zumdahl 13.13 • Outline • Concept behind VSEPR • Molecular geometries

  2. VSEPR Background • The Lewis Dot Structure approach provided some insight into molecular structure in terms of bonding, but what about geometry? • Recall from last lecture that we had two types of electron pairs: bonding and lone. • Valence Shell Electron Pair Repulsion (VSEPR). 3D structure is determined by minimizing repulsion of electron pairs.

  3. VSEPR Background (cont.) • Must consider both bonding and lone pairs in minimizing repulsion. • Example: CH4 Lewis Structure VSEPR Structure

  4. VSEPR Background (cont.) • Example: NH3 (both bonding and lone pairs). Lewis Structure VSEPR Structure

  5. VSEPR Applications • The previous examples illustrate the stratgey for applying VSEPR to predict molecular structure: 1. Construct the Lewis Dot Structure 2. Arranging bonding/lone electron pairs in space such that repulsions are minimized.

  6. VSEPR Applications (cont.) • Shorthand notation: 1. Refer to central atom as “A” 2. Attached atoms are referred to as “X” 3. Lone pairs are referred to as “E” • Examples: H2O: AX2E2 CH4: AX4 BF3: AX3 PCl5: AX5 NH3: AX3E ClF3: AX3E2

  7. VSEPR Applications • Linear Structures (AX2): angle between bonds is 180° • Example: BeF2 180°

  8. VSEPR Applications • Trigonal Planar Structures (AX3): angle between bonds is 120° • Example: BF3 120°

  9. VSEPR Background (cont.) • Pyramidal (AX3E): Bond angles are <120°, and structure is nonplanar due to repulsion lone-pair. • Example: NH3 107°

  10. VSEPR Applications • Tetrahedral (AX4): angle between bonds is ~109.5° • Example: CH4 109.5°

  11. VSEPR Applications • Tetrahedral: angle may vary from 109.5° exactly due to size differences between bonding and lone pair electron densities bonding pair lone pair

  12. VSEPR Applications • Classic example of tetrahedral angle shift from 109.5° is water (AX2E2): “bent”

  13. VSEPR Applications • Comparison of CH4 (AX4), NH3 (AX3E), and H2O (AX2E2):

  14. What is the approximate bond angle in SO2? A. 90° C. 120° D. 109.5° B. 180°

  15. VSEPR Applications • Trigonal Bipyramidal (AX5), 120° in plane, and two orbitals at 90° to plane. • Example, PCl5: 90° 120°

  16. VSEPR Applications • Octahedral (AX6): all angles are 90°. • Example, SF6: 90°

  17. Advanced VSEPR Applications • See-Saw versus Square Planar AX4E: See Saw AX4E2: Square Planar <120° 180° 90°

  18. Advanced VSEPR Applications • Square Planar versus “See Saw” See Saw No dipole moment Square Planar

  19. Advanced VSEPR Applications • Driving force for last structure was to maximize the angular separation of the lone pairs. Same effect occurs in I3- (AX2E3):

  20. What is the orientation of the ClF bonds in ClF3 (28 e-)? AX3E2 A B C

  21. +1 +1 0 0 -1 -1 Advanced VSEPR Applications • VSEPR and resonance structures. Must look at VSEPR structures for all resonance species to predict molecular properties. Example: O3 (AX2E): bent Dipole moment? Yes!

  22. VSEPR Applications • Provide the Lewis dot and VSEPR structures for CF2Cl2. Does it have a dipole moment? 32 e- Tetrahedral

  23. What is the expected shape of ICl2+? AX2E2 A. linear C. tetrahedral D. square planar B. bent

More Related