1. Lewis Dot Structures on Board Ionic uses charges (NaCl) Covalent 1: Find total # Valence e- 2: Each H gets 2, all others get 8 3: Line indicates shared pair of e- H2O – single bond CO2 – double bond N2 – triple bond

2. Single Bonds ___________ Double Bond ___________ Triple bond

3. Lewis Dot diagrams Practice

4. Molecular Geometry Seeing Molecules in 3-D

5. Molecular Geometry molecules are really 3-D!
CH4 in 2-D on a sheet of paper
CH4 looks like this in 3-D

6. How do we know the shape of molecules? X-Ray Crystallography

7. Valence Electrons determine Molecular “VSEPR” Shape
VSEPR = “Valence-Shell Electron Pair Repulsion”
Electron pairs (bonding or lone pairs) in a molecule repel each other and will try and get as far away from each other as possible… this determines the shape.
Lone pair electrons
bonding pair electrons
NH3 VSEPR shape in 3-D
NH3 in 2-D

8. 4 Shapes to Know
Tetrahedral
Trigonal Pyramidal
Bent
Linear

9. How Lone Pairs Affect Molecular Shape
“paddles” are lone pairs of electrons.
Remove the paddles and you can see the shapes.

10. Molecular Geometry

11. Shapes in Large Molecules
Large molecules are composed of the small shapes we’ve studied
Ex: tetrahedral

12. Why Shape Matters. SMELL
Ethyl Acetate (C4H8O2)
Butyric Acid (C4H8O2)
Same formula, but different shapes = very different smells
Rum extract smell
Rancid butter smell

13. Why Shape matters. TASTE (Sugar)

14. Why Shape matters (drugs)
Your body acclimates to drugs and it takes more and more to get the same feeling.

15. Molecular Polarity & Smell
Besides shape, polarity also plays a role in your ability to smell.
Polar molecules = smell
Non-polar = don’t smell
Your smell receptors are polar and surrounded by mucous (a watery substance)
Ex: Methane gas is odorless
-They add this polar stinky chemical to it so that you can smell it:

16. Determining Molecular Polarity
Draw correct VSEPR Shape
Determine if molecule is symmetrical.
If the molecule is symmetrical = non-polar
- no partial charges are needed!
If the molecule is NOT symmetrical = polar
- you must show partial charges.

17. Examples of Polar & Nonpolar Molecules

18. Molecular shape and Lewis Dot diagrams Practice

19. -Intramolecular forces = Bonding. within a molecule
-Intramolecular forces = Bonding within a molecule “Atom to Atom” -Intermolecular forces “Molecule to Molecule” 2 main types

20. -Intermolecular forces. 1) London Dispersion Forces
-Intermolecular forces 1) London Dispersion Forces 2) Dipole – Dipole Forces Hydrogen Bonding

21. Without these forces there would be no liquids or solids
Without these forces there would be no liquids or solids. Everything would be a gas.

22. 1) London Dispersion forces Temporary very weak attraction between electron clusters in Noble gases and nonpolar molecules. There is nothing else holding them together.

23. London Dispersion forces

24. 2) Dipole-Dipole forces Attraction between the positive and negative parts of different molecules.

25. Like Dissolves Like NaCl (Polar) dissolved in Water (Polar)

26. Like Dissolves Like Oil is non-polar

27. How does soap work? Polar and non-polar ends

28. 50 ml water plus 50 ml alcohol = ? ml

29. Water Hydrogen Bonding due to polarity Positive Hydrogen end attracted to Negative Oxygen end

30. Water Hydrogen Bonding due to polarity Positive Hydrogen end attracted to Negative Oxygen end

31. Water - Hydrogen Bonding Ice density - Water is most dense at 4oC

32. Water Hydrogen Bonding due to polarity Cohesion – Surface Tension

33. Properties of Water due to Hydrogen Bonding & Polarity
Cohesion – water molecules are attracted to one another
Causes water to be “Sticky”
This is why water forms droplets
Adhesion – water is attracted to other substances
Water will “stick” to containers & objects
Surface tension – strong forces between molecules cause the surface of a liquid to contract
Capillary action- water is attracted to other water molecules and will “rise”
“USGS Water Science for Schools: All about water!” US Geological Survey. 9 December

34. More properties…
Capillary Action – the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension.
Universal Solvent things dissolve in water- polarity
“USGS Water Science for Schools: All about water!” US Geological Survey. 9 December

35. Hydrogen Bonding due to polarity Viscosity

36. Nitrogen Hydrogen Bonding due to polarity Positive Hydrogen end attracted to Negative Nitrogen end

37. Hydrogen Bonding in Kevlar
Hydrogen bonding in Kevlar, a strong polymer used in bullet-proof vests.

38. Hydrogen Bonding in DNA

39. Effect on melting & boiling point
Effect on melting & boiling point. If the intermolecular forces are strong, you need more energy--and thus a higher melting point--to overcome them. Explanation: Meaning of melting point: The temperature at which a substance changes state from solid to liquid. So what is the purpose of intermolecular forces of attraction ? Holding two molecules together, which helps to keep the substance in a given state. If the intermolecular forces are strong, you need more energy to overcome them. In the case of melting points, the particles in a solid are held by intermolecular forces. To convert the solid into a liquid, you must overcome the intermolecular forces.

40. Melting
Some attractive forces holding the particles together are broken and particles move freely around each other but are still close together. The stronger these forces are, the more energy is needed to overcome them and the higher the melting temperature.
Boiling
The remaining attractive forces are broken so the particles can move freely and far apart. The stronger the attractive forces are, the more energy is needed to overcome them and the higher the boiling temperature.

41. Transfer Task