Homework

Charge Distribution, Polarity, and Bond Properties

Chapter 8: 7-10 Homework

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 8: Section 7-106.

Study Notes
• 8.7: Charge distribution within a bond depends on the electronegativity of the atoms involved. When the electronegativities are different, a bipolar bond forms, and the molecule is dipolar. In ionic compounds, the polarity is so strong that one of the atoms involved captures an electron from the other. In order to track the polarity of the charge distribution with in a molecule, we calculate the formal charge for each atom. The sum of the formal charges on each of the atoms equals the net charge on the molecule or on hand. When a net negative charge exists, it should reside on the most the electronegative atom in the molecule.
• 8.8: Polar molecules have a dipole moment, which is a measure of the "turning" force due to the existence of a locus (position in space) that attracts and a locus that repels. Symmetrical molecules have no dipole moment.
• 8.9:We classify bond properties according to order, length, and energy. Some practical rules guide our estimation of these properties in most circumstances. Bond order tells us how strong a bond will be: how difficult it will be to break. Bond length tells us how close the the atoms will be when the bond is complete. The length of the bond is also an indication of its strength. Bond energy is the work we have to do to break the bond.
• 8.10: Practical application of bonding properties and molecular shape led to the discovery of the structure of DNA. Because the repeating backbone of DNA linking phosphate to the carbon atoms in the ribose sugar molecule have a tetrahedral electron-pair geometry, the chain itself cannot be linear. This forces DNA to take on its characteristic heliacal shape.

Important Formulae

ConceptEquationNotes
Bond orderBO = shared pairs in X-Y bonds / X-Y links in molecule shared pairs: total pairs of electrons in bonds links: total bond connections X, Y: atoms of elements X and Y

Web Lecture

Read the following weblecture before chat: Charge Distribution and Molecular Polarity

Videos for Chapter 8: Chemical Bonds and Molecular Geometry

Review the Videos at Thinkwell Video Lessons.

• Under "Chemical Bonding: Fundamental Concepts: Resonance Structures and Formal Charge"
• Electronegativity, Formal Charge, and Resonance
• Under "Chemical Bonding: Fundamental Concepts: Bond Properties"
• Bond Properties
• Using Bond Dissociation Energies

Simulations

Use the pHET Model simulation below to build each of the molecular shapes in your text:

• linear (three atoms, two single bonds)
• bent (three atoms, two single bonds, two lone pairs)
• trigonal planar (three atoms around fourth central atom, three single bonds)
• trigonal pyramidal (three atoms around fourth central atom, three single bonds, one lone pair)
• tetrahedral (four atoms around fifth central atom, four single bonds)
• trigonal bipyramidal (five atoms around sixth central atom, five single bonds)
• octahedral (six atoms around seventh central atom, six single bonds)

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

• Required: Complete the Mastery exercise with a passing score of 85% or better.
• Go to the Moodle and take the quiz for this chapter.

LAB #6 GUIDED INQUIRY: Using qualitative methods to differentiate covalent and ionic bonds. -- Phase III

Post your formal report on your experiment. Include photographs of any models you created.

References

• APGIE Investigation 6: Bonding in Solids: Whatâ€™s in that Bottle?
• IGHCE Lab 19.3-4 Qualitative Analysis of Inorganic Cations and Anions
• Alternative Lab: Molecular Geometry