Trends+and+Forces

The powerpoint for this unit.



The basic pattern of logic in this unit works like this: 1. Notice an observable difference in a physical property (rate of evaporation, boiling point, solubility, viscosity, surface tension) 2. Decide on the relative strength of intermolecular forces 3. The stronger the intermolecular force, the greater the separation of positive and negative charges inside the molecule. 4. Examine the molecule structure for evidence of this separation of positive and negative charges. These steps work in both directions. You can look at a molecule (step 4) and then make predictions about intermolecular forces (step 1).

Strategies for writing good explanations on this topic
 * Refer to Coulomb's Law: the force of attraction between charges is directly proportional to the size of the charges and inversely proportional to the distance (squared) between the particles.
 * When explaining "in terms of atomic structure," make a statement about the nuclear charge, the valence electrons and inner core electrons.
 * When discussing the forces between molecules, explain whether each molecule is polar or not; don't forget that the strength of the dispersion force is directly proportional to the molecular mass.
 * In your analysis of polarity, keep an eye out for the molecules that have hydrogen bonded to N, O, F, or Cl. These molecules will experience exceptionally strong dipole-dipole attraction, which is called hydrogen-bonding.

Class work: A question from a previous AP exam:

Use the principles of atomic structure and/or chemical bonding to explain each of the following. In each part, your answer must include reference to __both__ structures. (a) The atomic radius of Li is larger than that of Be. (b) The second ionization energy of K is greater than the second ionization energy of Ca. (c) The carbon-to-carbon bond energy in C2H4 (ethene) is greater than it is in C2H6 (ethane). (d) The boiling point of Cl2 (chlorine) is lower than the boiling point of Br2 (bromine).

Please type your answers and e-mail the document to Mr. Robinson. trobinson@scischina.org

Homework sets for this unit. At end of Chapter 9, do problems 9.5, 9.7, 9.11, 9.13, 9.15, and 9.19 ||  ||
 * Date this was assigned || Due Date || Sections to Read || Homework Problems || Downloads ||
 * October 19 || October 23 || Read Sections 8.1, 8.3, and 8.5. Do not worry about understanding the concept of formal charge; we will discuss this in class. || At end of Chapter 8, do problems 8.43 and 8.51. Also, complete the Lewis Structure Review Sheet posted at the right. || [[file:Lewis structures review.pdf]] ||
 * October 25 || October 29 || Read Section 8.4. You will teach yourself about polar bonds. Check your understanding by completing the homework problems in THREE SECTIONS. || Read the pages listed below and then try the problems listed with that section before moving on to the next section.
 * Definition of Electronegativity on pages 285 and top of page 286. After reading, complete problems 8.31 and 8.33 (page 308).
 * Electronegativity and Bond Polarity, pages 286 and 287. After reading, complete problems 8.35, 8.37 and 8.76.
 * Dipole Moments are very carefully calculated physical quantities. If the concept is very confusing, you can skip this section and talk about it with me later in class. If you read it, try problem 8.39.
 * A VERY IMPORTANT little section to read is on page 290, Bond Types and Nomenclature. It talks about some of the gray areas in chemistry (few rules are black and white). Try problem 8.41 ||  ||
 * November 6 || November 14 ||  ||   || [[file:Octahedral Bipyrmidal Molecules.pdf]] ||
 * November 14 || November 16 || Read sections 1 and 2 in Chapter 11 || Do the following problems at the end of the chapter: 8, 9, 11, 13, 17, 19, 22, 78 and 80. ||  ||
 * November 16 || November 20 || This assignment will help you review shapes of molecules. Read 8.5, 8.6, 9.1, and 9.2, pay attention to the tables on p. 321 and p. 324 || At end of Chapter 8, do problems 8.43, 8.49, 8.57
 * November 16 || November 20 || This assignment will help you review molecule polarity. Reread Section 8.4 and then read Sections 9.3 and 9.4. || At end of Chapter 9, do problems 9.23, 9.25, 9.27, 9.67, and 9.72. An interesting challenge problem is 9.84, which is even harder than your typical AP exam problem. ||  ||
 * November 22 || November 26 || Read 8.8 || Finish the Hess' Law worksheet given to you by Mr. Robinson. Do the following problems at the end of Chapter 8: 8.61, 8.63, 8.67, 8.83, 8.84. ||  ||
 * November 30 || December 4 || Review sections 1 to 4 of Chapter 7 || At end of Chapter 7 in Brown LeMay, do problems 7, 11, 13, 17, 21, 27, 33, and 35. ||  ||
 * December 4 || December 6 || Review sections 1 to 4 and read section 5 of Chapter 7 || At end of Chapter 7 in Brown LeMay, do problems 8, 14, 21, 23, 24, 29, 31, 41 and 43. ||  ||
 * ===THE REST OF THIS TABLE CONTAINS ASSIGNMENTS FROM THE PAST. As we do them, I will move them to the top part of this table.=== ||
 * ||  ||   || On page 322 & 232 in Addison-Wesley, complete problems 42-48, 52-54, and 70-72. ||   ||
 * ||  ||   || This is a review worksheet for all thermochemistry problems. You can try problems 1 to 10 before Tuesday the 19 and the rest for Thursday the 21. || [[file:Thermochemistry Problems.rtf]] ||
 * ||  || Read 8.1 and 8.2 of Brown LeMay || At end of Chapter 8 in Brown LeMay, problems 8.7, 8.11, 8.13, 8.15, 8.17, 8.19 ||   ||