polarity of bonds and molecules mrs. huelin chemistry april 24, 2012
TRANSCRIPT
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