Lecture 12

1. Lecture 12 Molecular Shape 3.1 – 3.3 16-September Assigned HW 3.2, 3.4, 3.6. 3.8, 3.12, 3.16, 3.18, 3.20, 3.30 Due: Monday 20-Sept

2. Review 2.13-2.15 D4-D5 • Most bonds have some ionic character • Dipoles occur when one ionic configuration is preferred over the other • Bond polarity is due to differences in electronegativity (EN) • Electron pulling power of an atom • Same trend as electron affinity • Ionic bonds occur when ΔEN > 2 • When more than 2 atoms are present in a molecule, the polarity of the molecule is the sum of ΔEN for the individual bonds • Polarizability • Big anions are polarizable • Small, highly charged cations have high polarizing power • Naming binary compounds • More cationlike first followed by more anionlike. Use Greek prefixes.

3. Shapes of Molecules – VSEPR • Electrons in a lone pair or a bond repel each other • Valence Shell Electron Pair Repulsion Model Rules: • Regions with electrons (bonds and lone pairs) arrange themselves such that the distance between electron pairs is maximized • Make no distinctions between single and multiple bonds.

4. Shapes of Molecules Bond angle?

5. Shapes of Molecules – Trigonal Planar Bond angle?

6. Shapes of Molecules

7. Shapes of Molecules Phosphorus pentachloride

8. Shapes of Molecules Sulfur hexafluoride

9. Shapes of Molecules Carbonate

10. Shapes of Molecules – Multiple Central atoms Ethene

11. Shapes of Molecules - Lone Pairs What happens when the atom has lone pairs? Is the shape influenced? Why?

12. Shapes of Molecules – VSEPR • Electrons in a lone pair or a bond repel each other • Valence Shell Electron Pair Repulsion Model Rules: • Regions with electrons (bonds and lone pairs) arrange themselves such that the distance between electron pairs is maximized • Make no distinctions between single and multiple bonds. • All regions of electrons are included in the electron arrangement, but ONLY atom positions are considered when picking a shape.

13. Shapes of Molecules - Lone Pairs What happens when the atom has lone pairs? Is the shape influenced? Why? Lewis Structure Electron Arrangement Shape

14. Shapes of Molecules - Lone Pairs

15. Shapes of Molecules - Lone Pairs What should the bond angle be? 107.5 instead of 109.5 Why? Electron Arrangement Shape

16. Shapes of Molecules – VSEPR Rules: • Regions with electrons (bonds and lone pairs) arrange themselves such that the distance between electron pairs is maximized • Make no distinctions between single and multiple bonds. • All regions of electrons are included in the electron arrangement, but ONLY atom positions are considered when picking a shape. • Repulsion strengths follow the trend LP-LP > LP-atom > atom-atom

17. VSEPR Forumla A common formula, the VSEPR formula, is often used to identify arrangement of atoms (Xn) and lone pairs (Em) around an atom (A) AXnEm H  AX O  AX2E2 H  C  P  Cl 

18. Shapes of Molecules – VSEPR Predict the shape of SeCl4 • Lewis Structure 2. VSEPR Formula 3. Predict Orbital 4. Account for Lone • Geometry Pairs Se  AX4E

19. Shapes of Molecules – VSEPR Predict the shape of SeCl4 • Lewis Structure 2. VSEPR Formula 3. Predict Orbital 4. Account for Lone • Geometry Pairs Se  AX4E

20. Shapes of Molecules – VSEPR Predict the shape of SeCl4 • Lewis Structure 2. VSEPR Formula 3. Predict Orbital 4. Account for Lone • Geometry Pairs Se  AX4E

21. Shapes of Molecules - Lone Pairs So why is water polar? net

22. Shapes of Molecules – VSEPR

23. Shapes of Molecules – VSEPR

24. Shapes of Molecules – VSEPR