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

2. Polarity • of bonds … • HCl • H2O • of molecules … • H2O • CO2

3. For each molecule, draw the Lewis structure, predict the shape and bond angle, and identify as polar or nonpolar. • Br2 • HCN • C2H2 • NH4+ • H2S • PF3 • CH2O • MgO

4. Electronegativity differences indicate Polarity

5. Electronegativity difference (∆En) 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 (C2H6). • 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=DVCYlST6mYQ

9. Review Ionic and Covalent Compounds • Practice Quiz and Graphics: http://www.elmhurst.edu/~chm/vchembook/145Areview.html

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

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 • Which substance contains both covalent and ionic bonds? • NH4NO3 • CH3OCH3 • LiF • CaCl2 • Which of these bonds is most polar? • H-Cl • H-Br • H-F • H-I • Which of these molecules can form a hydrogen bond with a water molecule? • N2 • NH3 • O2 • CH4