Intermolecular Forces

Chapter 11: 1-3 Homework

• Reading Preparation
• WebLecture
• Study Activity
• Preparation work for chat
• Online Quiz
• Lab Instructions

Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 11: Sections 1 to 3

Study Notes

Intermolecular forces called van der Waals forces hold molecules together to form solids. As with all chemical "bonds", the forces have their basis in electrical charges, in the electrons in their shells and protons of the nucleus of the atoms. But the bonds between molecules are much weaker than the electron-sharing bonds within molecules that we studied in chapters 7-9.

• 11.1 The strength of intermolecular bonds determine whether molecules can form solids or liquids at a given temperature, and so determine the melting and boiling points of substances, as well as their solubility. Molecules form bonds with other molecules when there are charge differences either with the whole molecule, or within part of the molecule, even if those differences are of short duration.
• 11.2 Ion-dipole permanent charges: Recall Coulomb's law for electrical forces: F_e = kQq/r². This rule governs all electrical forces, which will be attractive if q and Q have opposite signs (negative electrical force = attraction), and repulsive if q and Q have the same sign (positive electrical force = repulsion). It explains why
  • the closer the centers of charge difference are, the greater the force between them.
  • the greater the charge on the centers of charge, the greater the force between them.

  Examples of ion-dipole situations include whenever a metal ion bonds to polar water molecules to form hydrated salts.

• 11.3 Dipole-Dipole permanent charges. The types of intermolecular bonds that involve permanent polarity are
  • dipole-dipole : water and ethanol are both polar molecules with permanent internal areas of net charge. The negative area of one molecule attracts the positive area of the other.
  • hydrogen bonds : When hydrogen bonds its single electron to form molecules with oxygen, fluorine, chlorine, or nitrogen, the high electronegativity of the non-metal atom pulls the hydrogen electron into a localized bond position between the hydrogen and the non-metal, leaving the single proton of the hydrogen "unshielded" by any electrons. This positive charge concentration attracts negatively-charged areas of other atoms to form hydrogen bonds. H-bonds of of major importance in organic molecules, holding DNA strands together and prescribing the shapes of polypeptide chains as they form proteins.

Web Lecture

Read the following weblecture before chat: Intermolecular Forces

Study Activity

Chat Preparation Activities

• Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

Chapter Quiz

• There is no chapter quiz YET.

---

Lab Work

(Aligns to) AP #8 GUIDED INQUIRY — Measuring the deviation of real gases from the ideal gas law — Phase III

Carry out your procedures to test your predictions for gas behavior, and consolidate your experimental results in a formal report.

References:

• IGHCE Lab 14.1 OR HSCKM VIII-1: Volume-Pressure relationships (Boyle's Law)
• IGHCE Lab 14.2 OR HSCKM VIII-2: Volume-Temperature relationships (Charles' Law)
• IGHCE Lab 14.3 Pressure-Temperature relationship (Gay-Lussac's Law)
• Alternate Labs (two): Gas Volumes and Gas Generation

---

© 2005 - 2024 This course is offered through Scholars Online, a non-profit organization supporting classical Christian education through online courses. Permission to copy course content (lessons and labs) for personal study is granted to students currently or formerly enrolled in the course through Scholars Online. Reproduction for any other purpose, without the express written consent of the author, is prohibited.