HW From textbook “CHEMISTRY a Contemporary Approach”

• Read “Polar and Nonpolar Molecules” p124

• Do  exercise 3.3 p126

• Read “Dipole-Dipole Forces” p128-130

• Do questions 4,7,11,13,16,20,23,28,30,31,32,35 p139-142

The distribution of charge within a molecule indicates if the molecule is polar or nonpolar

A molecule is nonpolar when there is even distribution of charge creating symmetry.

Example 1: CO₂ and CH₄

 

           

Example 2: H₂ ,O₂, and N₂ 

 

       

A molecule is polar when there is uneven distribution of charge creating asymmetry.

Example:  HCl, NH₃, and H₂O. 

 

             

Note: The shape of the water molecule is said to be "bent"

Intermolecular forces are electrostatic attractions formed between opposite charge among molecules.

Hydrogen bonding is the strongest intermolecular force among polar molecules. It forms when a polar molecule containing either F, O, or N atom is attracted to the H of another molecule.

    Example: H₂O

    Example: NH₃

Example: HF

The higher the degree of polarity in the bonds the stronger the intermolecular forces are.

    Example:

    The intermolecular attractions are stronger among molecules of HBr than among molecules of HI                                     

    Example:

    The intermolecular attractions are stronger among molecules of H₂S than among molecules of H₂Se                                     

Intermolecular forces also exist among nonpolar molecules such as O₂ and N₂. A nonpolar molecule can temporarily acquire a dipole when electrons occupy one side of the molecule more than the other. Intermolecular forces among nonpolar molecules are the weakest intermolecular forces.

    Example: O₂

    Example: N₂

 TEST YOUR UNDERSTANDING

1/07

6/06

8/06

1/05

12 Which formula represents a nonpolar molecule? (1) HCl (2) H₂O (3) NH₃ (4) CF₄

Base your answers to questions 51 through 52 on your knowledge of chemical bonding and on the Lewis electron-dot diagrams of H₂S, CO₂, and F₂ below.

51 Which atom, when bonded as shown, has the same electron configuration as an atom of argon?

52 Explain, in terms of structure and/or distribution of charge, why CO₂ is a nonpolar molecule.

1/04

10 Which molecule is nonpolar? (1) H₂O (2) NH₃ (3) CO (4) CO₂

20 Which of the following compounds has the highest boiling point? (1) H₂O (2) H₂S (3) H₂Se (4) H₂Te

6/04

10 Which type of molecule is CF₄?
    (1) polar, with a symmetrical distribution of charge     (3) nonpolar, with a symmetrical distribution of charge

    (2) polar, with an asymmetrical distribution of charge (4) nonpolar, with an asymmetrical distribution of charge

8/04

16 Molecules in a sample of NH₃(l) are held closely together by intermolecular forces

                (1) existing between ions                                                    (2) existing between electrons

                (3) caused by different numbers of neutrons                  (4) caused by unequal charge distribution

41 Based on intermolecular forces, which of these substances would have the highest boiling point?  (1) He (2) O₂ (3) CH₄ (4) NH₃

1/03

45 Each molecule listed below is formed by sharing electrons between atoms when the atoms within the molecule are bonded together.

Molecule A: Cl₂         Molecule B: CCl₄         Molecule C: NH₃

        1. Draw the electron-dot (Lewis) structure for the NH₃ molecule.

        2. Explain why CC1₄ is classified as a nonpolar molecule.

        3. Explain why NH₃, has stronger intermolecular forces of attraction than Cl₂

        4. Explain how the bonding in KCl is different from the bonding in molecules A, B, and C.

8/03

15 Which of these substances has the strongest intermolecular forces? (1) H₂O 3) H₂Se  (2) H₂S ( (4) H₂Te

6/02

The strongest forces of attraction occur between molecules of   (1) HCl              (2) HF         (3) HBr               (4) HI

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