Annoucements
TEST ON WEDNESDAY 13 April--NOT MONDAY.
Chapter 12. Visit the essential study partner.
Chapter 12 pretest is here!!
WebAssign for chapter 12 is up. You should be able to do much of it.
Remember:
There are two types of bonds: ionic and covalent.
Ionic bonds are the electrostatic attraction between positive and negative ions.
Covalent bonds are a pair of electrons shared between two atoms.
There are two types of covalent species
- Molecular covalent. These molecules attract one another by intermolecular forces. The three types of intermolecular forces are:
- Dispersion Forces--weakest. Present in all molecules. Increaseses with number of electrons in molecule (and therefore increases with molecular weight)
- Dipole-dipole forces--attraction between polar covalent molecules
- Hydrogen bonding--attraction between lone pair on O, N or F and hydrogen bonded to O, N or F
- Network Covalent. These are covalent macromolecules. One molecule is many atoms large. These compounds have high bp and mp. Examples are diamond, graphite, silicon dioxide.
To decide which type of intermolecular force is present requires proficiency at drawing Lewis Structures and predicting molecular geometry. In addition you must apply your understanding of electronegativity.
Remember:
- Like Dissolves like. That means that POLAR solvents dissolve POLAR solutes, and NONPOLAR solvents dissolve NONPOLAR SOLUTES.
- MISCIBLE liquids mix while IMMISCIBLE liquids do not (oil and water)
- boiling point elevation = iKfm
- Where i is the Vant Hoff factor
- Kf is the molal freezing constant
- m is the molality
- Freezing poin depression = iKbm
- Where i is the Vant Hoff factor
- Kb is the molal boiling constant
- m is the molality
