Polarity of Bonds and Molecules

Mrs. Huelin ChemistryApril 24,

2012

Polarityof bonds …HCl

H2O

of molecules …H2O

CO2

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

Electronegativity differences indicate Polarity

Electronegativity difference (∆En) and Bond type

For each pair of elements, calculate the electronegativity difference and label the bond type (polar covalent, nonpolar covalent, or ionic).H, ClH, SS, ClNa, FCl, BrAl, 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 (C2H6).

C-C = 347 kJ/molC-H = 393 kJ/mol

VIDEO LESSONWater, a polar molecule, on YouTube:

http://www.youtube.com/watch?v=DVCYlST6mYQ

REVIEWIonic and Covalent Compounds

Practice Quiz and Graphics: http://www.elmhurst.edu/~chm/vchembook/145Areview.html

Internet resourcesMolecular 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

Properties of Covalent CompoundsLow 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 Review1. Which

substance contains both covalent and ionic bonds?

a) NH4NO3

b) CH3OCH3

c) LiFd) CaCl2

2. Which of these bonds is most polar?

a) H-Clb) H-Brc) H-Fd) H-I

3. Which of these molecules can form a hydrogen bond with a water molecule?

a) N2

b) NH3

c) O2

d) CH4