1. Molecular Geometry and Polarity

2. Molecule  Covalent Bond
- shared electron pairs
Most atoms have four areas for electron density (Exceptions: H and He)

3. - electron behavior – repel each other
- Result: spread evenly around atom
– forms a Tetrahedron – angles = 109.5
Tetrahedrons can be perfect or imperfect
Perfect – even distribution – all orbitals are the same
Imperfect – uneven distribution – all orbitals are not the same

4. Shape influenced by the types of orbitals Shared vs. Unshared
Shared – between two atoms
Unshared – around one atom
Shared are smaller because the 2 nuclei pull on the orbital making it have a narrower diameter
Changes the angles between the bond axis in a molecule with a mixture of shared and unshared orbitals
Shared orbitals are SMALLER than Unshared orbitals

5. Ex: Dihydrogen Monoxide

6. Why?: electrons in a shared orbital pass between two atoms
pulled on by two nuclei
causes the orbital to be narrower
Ex: pull on a balloon on both ends rather than one end
RESULT: Unshared orbitals take up more space and push the shared orbitals closer together

7. Repulsion Hierarchy:
unshared and unshared > unshared and shared > shared and shared

8. Unshared
Shared

10. Importance of Bond Angles
- influences the interaction of molecules
- lead to the difference of a molecule being a solid, a liquid or a gas at room temperature and how it will react with other substances

11. Molecular Interactions
Intramolecular Bonds
- covalent bonds between two atoms
Intermolecular Bonds
- weak attractive forces between two molecules
- the stronger an intermolecular bond – the more a substance will bond together

12. Determination of Intermolecular Bonds
1. Polar Bond Formation: Oxygen and Hydrogen
- electrons spend more time around oxygen
- makes oxygen slightly negative
- makes Hydrogen slightly positive
RESULT = POLAR COVALENT BOND
E-neg = 2.1
E-neg = 3.5

13. - covalent bond that results from the unequal sharing of electrons
- result is a bond with a positive and negative end (poles)
- called a dipole moment
- may give the molecule distinct poles of positive and negative charge if the charges are asymmetrically balanced

14. EX: H2O vs CO2 vs. Cl2
H2O:
Difference in electronegativity = Bonds are polar
Charges are asymmetrical = Molecule is polar

15. EX: H2O vs CO2 vs. Cl2
CO2: Difference in electronegativity = Bonds are polar
Charges are symmetrical (Cancel each other) = Non-Polar Molecule

16. EX: H2O vs CO2 vs. Cl2
Cl2: No difference in electronegativity = Non-polar bonds = Non-polar molecule

17. Result of Dipole Forces: Intermolecular Bonding
Dipole-Dipole Forces: Intermolecular
Attraction between the slightly positive and slightly negative poles
Specific: Hydrogen Bond

19. Importance of Polarity
1. Binds molecules together
Stronger = More Solid
2. Separation of Substances = FRACTIONATION
- Chromatography
- can determine the chemical make up of a mixture

20. Chromatography
Animation
Animation II

21. 3. Characteristics of Water
a. Cohesion: water sticking to itself – surface tension

22. Characteristics of Water
Adhesion: water sticking to other things – capillary action

23. Cohesion-Adhesion Theory of Transpiration

24. c. High specific heat –
Specific Heat – amount of heat a substance can absorb before it changes temperature
High Specific Heat of Water (4.186 J/goC)
- Ethanol = 2.46 J/goC
Result:
Climate Control – water heats and cools slowly which keeps land masses near bodies of water more temperate
Evaporative Cooling – sweating – it takes a lot heat to cause the water to evaporate – heat is lost when the water leaves

25. Less dense as a solid – as water cools the hydrogen bonds between the molecules get stronger making the molecule assume a strict lattice structure
– in this form the water molecules are more spread out and have a greater volume
- equal mass over a greater volume = less dense  ice floats
- good for aquatic biomes – prevents bodies of water from freezing solid  happy fish

27. e. Solvent – water breaks apart substances – good for chemical reactions because the atoms can interact more easily if they are spread out
– very important for the metabolism of cells -