2. Example 1: CO 2 First look at the bond C - O 3.5 - 2.5 = 1.0 Bond is polar Draw dipole Draw Lewis structure What shape? Linear Draw dipoles Dipoles cancel, thus the molecule is non-polar C O O x x x x x x x x x x x x

3. Example 2: H 2 O First look at the bond H - O 3.5 - 2.1 = 1.4 Bond is polar Draw dipole Draw Lewis structure What shape? Bent Draw dipoles The O end is negative and the H end is positive, thus it is polar δ - δ + H O x x H O H H

4. CF 4 C - F 4.0 - 2.5 = 1.5 Tetrahedral Dipoles cancel, thus the molecule is non-polar C x x x x x x x x F x x x x x x x F x x x x x x F x x x x x x x F C F F F F

5. NH 3 N - H 3.0 - 2.1 = 0.9 δ - δ + The N end is negative and the H end is positive, thus it is polar N x x x H H H N H H H

11. Dipole-Dipole interactions Ex: HCl H - Cl 3.0 - 2.1 = 0.9 δ - δ + Line up another molecule Covalent bond very strong, takes lots of energy to break Dipole-Dipole interaction, much weaker and takes less energy to break H - Cl δ - δ + H - Cl δ - δ + Cl - H δ - δ + Cl - H δ - δ +

12. Hydrogen Bond H - O 3.5 - 2.1 =1.4 Leaves behind a relatively unshielded p + p + bonds to a lone pair on another molecule This is called a hydrogen bond It only forms if the atom that H bonds to has a very high EN Forms when H is bonded with F, O and N

13. H 2 O p + p + H Bond This is why water has very strong cohesion O H H O H H

15. Example: Helium Boiling point = -269 ᵒC How can He be a liquid? He What if the 2 e - are on the same side of the atom? Forms a instantaneous dipole He Induces a dipole of the other He δ - δ + δ - δ + Called an instantaneous induced dipole Or London force 2 p + 2 p +

18. Example: What force of attraction is found in CaO? Is it weak or strong? Ca Second: classify the bond O 1.0 3.5 2.5 Ionic First: look for covalent networks or H bonds Isn’t C or SiO 2 not a network Doesn’t have H - not H bonding Strong force

19. Example: What force of attraction is found in CH 3 OH? Is it weak or strong? Not a network Has H bonded to O H bonding Weak force

20. Example: What force of attraction is found in CH 4 ? Is it weak or strong? Not a network Has H - but not bonded to O, N or F C H 2.5 2.1 0.4 Polar bond

21. Now look at the molecule Lewis structure Tetrahedral It is symmetrical - so nonpolar molecule London forces Weak force C x x x x H H H H C H H H H

22. Example: What force of attraction is found in PCl 3 ? Is it weak or strong? Not a network No H P Cl 2.1 3.0 0.9 Polar bond

23. Lewis structure Triangular pyramidal δ - δ + Asymmetrical - so polar molecule Dipole-dipole interaction Weak force P x x x Cl Cl Cl P Cl Cl Cl

24. P P x x x x x x Cl x Cl Cl Cl Cl Cl C H H H P Cl Cl Cl H