Polar Bonds and Molecular Shapes Chemistry 11 Ms. McGrath

Question? Are all molecules that have polar bonds polar molecules? Let’s answer this question by comparing the properties of two common compounds – water and carbon dioxide.

Water and Carbon Dioxide Water is a liquid at room temperature. Water droplets are nearly spherical when falling. These facts indicate that water molecules are strongly attracted to each other. Carbon dioxide is a gas at room temperature. These molecules appear to have very little attraction for each other.

Water and Carbon Dioxide However, both molecules have 3 atoms each. To determine the difference in properties, lets examine the bonds in each molecule.

Water The bent shape of water (with the lone electron pairs) results in a partially positive end near the hydrogen atoms and a partially positive end near the oxygen end. Therefore making water polar.

Carbon dioxide The direction of the arrows indicating the electronegativity are in opposite directions. One bond cancels the polar effect of the other. Therefore carbon dioxide is nonpolar.

Polar molecules - examples  Water (H 2 O)  Ammonia (NH 3 )  Sulfur dioxide (SO 2 )  Hydrogen sulfide (H 2 S) Non polar molecules  Carbon dioxide (CO 2 )  Hydrogen gas (H 2 )  Methane (CH 4 )  Ethylene (C 2 H 2 )

Nonpolar molecules - examples  Carbon dioxide (CO 2 )  Hydrogen gas (H 2 )  Methane (CH 4 )  Ethylene (C 2 H 2 )

Polarity and Molecules  See the table on page 196 that indicates which shapes are molecular and which are not. Now try page 196, #8, 9, 10