After that, let's make sure you have grades in the gradebook for last week's homework.
p. 132 #14-17, p. 136 #18-20
I need your rough drafts today so you can get them back tomorrow. If you don't have them, then you better make sure that final draft is on point. Remember, written labs get sent to the IB for external assessment.
2. Review: Resonance & Giant Molecular Structures
3. Intermolecular forces
Lesson Objectives. By the end of this lesson, you should be able to:
1. List and describe all the intermolecular forces and determine their presence in certain compounds.
Links: VSEPR Theory Molecular Geometry Intermolecular Forces
Textbook Readings: Chapter 4.
Mission 1: What's Keeping Us Together Other Than Love? Covalent bonds holds atoms together within molecules, but what forces hold molecules together? The answer depends on the polarity and size of the molecules involved, and so said intermolecular forces will vary. The strength of intermolecular forces determine the physical properties of a substance. Volatility, solubility, and conductivity can all be predicted and explained from knowledge of the nature of intermolecular forces.
Dispersion forces (aka London forces): These are weak forces of attraction that occur between opposite ends of two temporary dipoles, usually with nonpolar molecules. A dipole occurs when the density of an electron cloud at any one moment be greater in one region of a molecule or atom. These dipoles are called temporary or instantaneous because they do not last long. When temporary dipoles influence the electron behavior of a nearby atom or molecule, induced dipoles result. Examine the images on page 149.
Dipole-dipole forces: Polar molecules that have a permanent separation of charge within their bonds as a result of electronegative differences have dipole-dipole attractions. Water has a clear positive end and a clear negative end. This is called a permanent dipole. When it bonds with another water molecule, a dipole-dipole attraction results. The strength varies depending on the distance and orientation of the dipoles.
The umbrella term van der Waals includes both dipole-dipole and dispersion forces.
Hydrogen bonding: When a molecule contains hydrogen covalently bonded to a very electronegative atom (fluorine, oxygen, or nitrogen), these molecules are attracted to each other by a particularly strong force called a hydrogen bond. These are specific instances of dipole-dipole attraction. The large electronegativity difference results in the electron pair being pulled away from hydrogen. It now exerts a strong attractive force on a lone pair of electrons in a nearby molecule.
Hydrogen bonds are the strongest intermolecular force. As a result, they cause the boiling points of substances to be higher than normal.