Molecular Interactions & Geometry Objectives

Introduction:

            This unit will cover the how the number of bonds in covalent molecules shapes the 3-D shape of the molecule, how electronegativity differences allow for dipoles to form, how the sum of dipole forces determine the polarity of the molecule, and how molecules and ions interact through weak connections called molecular interactions.
 

Terms:  You should be able to define and give examples for the following terms:

lone vs. non-bonding electron pairs, molecular polarity (nonpolar, polar, dipole, charge vectors), sigma minus & plus, ion-dipole, dipole-dipole, induced dipole-dipole, induced dipole- induced dipole, hydrogen bond, solvent, solute, dilute, saturated, insoluble, surface tension, adhesive, cohesive, capillary action.
 

Objectives:  These basic skills should be mastered. This means you need to WRITE out the answers to these objectives- the form the written review takes is up to you. It can be an outline, idea web, flashcards, short answer, etc.
 

1. Determine the direction of polarity of a polar bond based on electronegativity differences.

2. Distinguish between a polar and nonpolar covalent molecule. Be able identify a bond's polarity given the element's position on the periodic table.

3. Distinguish between and rank the relative strengths of ion-dipole, dipole-dipole, induced dipole-dipole, & induced dipole- induced dipole interactions.

4. Given a molecular formula and the periodic table, be able to predict and draw the 3-D structure of the molecule using "stick" covalent bonds and showing the location of nonbonding pairs. For "4 blob" central atoms, be able to use the "wedge" and "ladder" designations of bond orientation. Knowing the polarity and orientation of the bonds in a molecule, determine the overall polarity of the molecule using vector addition.

   5. Explain how hydrogen bonding (a specific dipole-dipole molecular attraction) plays a role in:

       > the freezing of water in creating a solid that floats (ice; see p.172-73 for a reminder)

       > the high boiling point of water relative to it�s mass

       > the ability of water to remain a fluid on earth

       > the ability of water to dissolve ionic & polar substances

       > the ability of water to induce dipoles in oxygen and carbon dioxide

       > the ability of water to transport dissolved substances

       > creating surface tension
 

6. Discuss why water's polarity is crucial for life on earth. Give specific examples based on the roles specified above in #5.

7. Explain how solvents and solutes interact. Explain how the design of the Lava lamp is a good example of these principles at work.

8. Given a solute�s molecular structure, be able to choose the best solvent. Explain how solubility changes with temperature.

10. Describe how to use solvents to separate molecules based on their mass and polarities.

11. Explain how soaps & detergents work. How do they make water �wetter�?