Chemistry H handouts

Recent Handouts Chapter 11 pretest

Annoucements

TEST ON WEDNESDAY--NOT MONDAY. THIS APPLIES TO ALL CHEMISTRY H CLASSES!!!!

Chapter 11. Visit the essential study partner.

Chapter 11 pretest is here!!

WebAssign for chapter 11 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

1. 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
2. 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.

Electronegativity is a measure of how well an atom attracts electrons when bonded to a different atom. F is the highest = 4.0, and other values are relative to F. O is the next most, and then N and Cl are the next most.

Molecular geometries:

Remember:

1. Draw the Lewis Structure
2. Count the number of bonded atoms (not number of bonds) and lone pairs on the central atom
3. Put the atoms and lone pairs in the correct geometry.

   Bonded Atoms (B) + Lone Pairs (E) =	Hybridization	Electronic Symmetry
   2	sp	linear
   3	sp2	trigonal planar
   4	sp3	tetrahedral
   5	sp3d	trigonal bipyramidal
   6	sp3d2	octahedral

4. Discount lone pairs when naming the molecular shape.

   Visit the University of Oregon website to get an excellent visual explanation of bonding. Rotate the different molecules yourself and view and hide the lone pairs. The Chime Plugin is required to view. This is available from MDL software with a free registration.

   Another useful site for VSEPR is the Chang website. It has a shockwave movie that covers every possible situation from the above table. In addition there is an interactive determining molecular shapes tutorial on the same page.

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