5.11 – Intermolecular Forces


We've already taken a brief look at the forces of attraction between molecules.  Today we will practice some of these key ideas and try to cement it into our brains.

Learning Objectives

  • Identify the intermolecular attractive interactions (dispersion, dipole–dipole, hydrogen bonding, ion–dipole) that exist between molecules or ions based on their composition and molecular structure and compare the relative strengths of these intermolecular forces. (11.2)
  • Explain the concept of polarizability and how it relates to dispersion forces. (11.2)

To become familiar with the topics presented in this mission, view the slides below and take note of the key ideas.  These are from sections 11.1-11.2 of your text.

Now work through the practice problems, and post your work to OneNote.

Work out these mastery problems and check your answers in OneNote.  Post your work when finished, including any corrections.  These questions are from the text and a released AP Exam.

11.10 

(a) How does the average kinetic energy of molecules compare with the average energy of attraction between molecules in solids, liquids, and gases?

(b) Why does increasing the temperature cause a solid substance to change in succession from a solid to a liquid to a gas?

(c) What happens to a gas if you put it under extremely high pressure?

  

11.16  What type of intermolecular force accounts for the following differences in each case?

(a) CH3OH boils at 65°C, CH3SH boils at 6°C

(b) Xe is liquid at atmospheric pressure and 120K, whereas Ar is a gas.

(c) Kr, atomic weight 84, boils at 120.9 K, whereas Cl2, molecular weight 71, boils at 238K

(d) Acetone boils at 56°C, whereas 2-methylpropane boils at -12°C.

  

11.19  Which member of the following pairs has the larger London dispersion forces?

(a) H2O or H2S

(b) CO2 or CO

(c) SiH4 or GeH4

 

11.26  Identify the types of intermolecular forces present in each of the following substances, and select the substance in each pair that has the higher boiling point.  Justify your responses.

(a) C6H14 or C8H18

 (b) C3H8 or CH3OCH3

 (c) HOOH or HSSH

 (d) NH2NH2 or CH3CH3

 

2013 FRQ #6

 

That's it!  All done with the atomic structure/bonding unit :)