1. Polarity of Bonds and Molecules Mrs. Huelin Chemistry April 24, 2012

2. Polarity of bonds … HCl H 2 O of molecules … H 2 O CO 2

3. For each molecule, draw the Lewis structure, predict the shape and bond angle, and identify as polar or nonpolar. Br 2 HCN C 2 H 2 NH 4 + H 2 S PF 3 CH 2 O MgO

4. Electronegativity differences indicate Polarity

5. Electronegativity difference (∆E n ) and Bond type

6. For each pair of elements, calculate the electronegativity difference and label the bond type (polar covalent, nonpolar covalent, or ionic). H, Cl H, S S, Cl Na, F Cl, Br Al, Br

7. Energy Practice Problem Given the following bond dissociation energy values, calculate the total energy that would be required to break all of the covalent bonds in 0.25 mol of ethane (C 2 H 6 ). C-C = 347 kJ/mol C-H = 393 kJ/mol

8. VIDEO LESSON Water, a polar molecule, on YouTube: http://www.youtube.com/watch?v=DVCYlST6 mYQ http://www.youtube.com/watch?v=DVCYlST6 mYQ

9. REVIEW Ionic and Covalent Compounds Practice Quiz and Graphics: http://www.elmhurst.edu/~chm/vchembook/1 45Areview.html http://www.elmhurst.edu/~chm/vchembook/1 45Areview.html

10. Internet resources Molecular polarity: http://www.elmhurst.edu/~chm/vchembook/210polarity.html http://www.elmhurst.edu/~chm/vchembook/210polarity.html Polar covalent compounds: http://www.elmhurst.edu/~chm/vchembook/152Apolar.html http://www.elmhurst.edu/~chm/vchembook/152Apolar.html Nonpolar covalent compounds: http://www.elmhurst.edu/~chm/vchembook/150Anpcovalent. html http://www.elmhurst.edu/~chm/vchembook/150Anpcovalent. html Ionic compounds: http://www.elmhurst.edu/~chm/vchembook/143Aioniccpds.h tml http://www.elmhurst.edu/~chm/vchembook/143Aioniccpds.h tml Compare Ionic, Polar, and Nonpolar Bonds: http://www.elmhurst.edu/~chm/vchembook/153Acompare.ht ml http://www.elmhurst.edu/~chm/vchembook/153Acompare.ht ml

11. Properties of Covalent Compounds Low melting and boiling points (melting sugar, not salt) Many exist as gases or vaporize readily at room temperature (oxygen, carbon dioxide) Form relatively soft solids (paraffin wax)

12. Forces of Attraction Intramolecular forces (bonding forces) Covalent bond is strong (sharing of electrons) Covalent network solids = brittle, nonconductors, extremely hard, very high melting point (diamond, quartz) Intermolecular forces (a.k.a. van der Waals forces)  Dispersion (induced dipole) = between nonpolar molecules  Dipole-dipole = between polar molecules  Hydrogen bond = between hydrogen on one molecule and fluorine, oxygen, or nitrogen on another

13. Multiple Choice Review 1. Which substance contains both covalent and ionic bonds? a)NH 4 NO 3 b)CH 3 OCH 3 c)LiF d)CaCl 2 2. Which of these bonds is most polar? a)H-Cl b)H-Br c)H-F d)H-I 3. Which of these molecules can form a hydrogen bond with a water molecule? a)N 2 b)NH 3 c)O 2 d)CH 4