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

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

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

Electronegativity differences indicate Polarity

Electronegativity difference (∆E n ) and Bond type

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

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

VIDEO LESSON Water, a polar molecule, on YouTube: mYQ mYQ

REVIEW Ionic and Covalent Compounds Practice Quiz and Graphics: 45Areview.html 45Areview.html

Internet resources Molecular polarity: Polar covalent compounds: Nonpolar covalent compounds: html html Ionic compounds: tml tml Compare Ionic, Polar, and Nonpolar Bonds: ml ml

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)

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

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