Polarity Notes

February 5, 2014

• Students will be able to define and identify: – Bond polarity and overall molecular polarity– Intermolecular forces.

• Lewis/Polarity/IMF/Geometry Lab

• Video of the day: The Big Three– Methane– Water– Ammonia

Introduction: Polarity

• Polarity is a concentration of charge on one side of a bond

• Some molecules have negative or positive poles, like magnets

Individual bond polarity• Polarity is determined by electronegativity

difference • To draw individual bond polarity:– Compare: Only two atoms at a time– The more electronegative atom attracts electrons

more– Draw arrow towards the more electronegative atom

http://www.youtube.com/watch?v=_M9khs87xQ8

Review: Electronegativity

• Electronegativity is the measure of how well an atom in a bond attracts electrons

• Electronegativity increases up and right across the periodic table

Are there lone pairs on the center atom?

Yes No

Polar Are the peripheral (outer) atoms

different?

Yes No

Polar Nonpolar

Overall Polarity

Bond Polarity Examples

Cl2

• Cl has the same electronegativity as Cl. We cannot draw an arrow to show polarity.

• The molecule is nonpolar.

Polarity Examples

• CH3I

• C has a higher electronegativity than H. We draw arrows from each H towards C.

• I has a higher electronegativity than C. We draw an arrow from C towards I.

• There are no lone pairs around the central atom and the outer atoms are different. The molecule is POLAR.

Polarity Examples• CH2O

• C has a higher electronegativity than H. We draw arrows from each H towards C.

• O has a higher electronegativity than C. We draw an arrow from C towards O.• There are no lone pairs around the central atom and the outer atoms are

different. The molecule is POLAR.

Polarity Examples

• O3

• O has the same electronegativity as O. We cannot draw arrows to show polarity.

• The central atom has a lone pair, so the molecule is polar.

Polarity Examples

• PF3

• F is more electronegative than P. We draw an arrow from P to each of the fluorine atoms.

• The central atom has a lone pair, so the molecule is polar.

Polarity Examples

• NH4+

• N is more electronegative than H. We draw an arrow from each H towards N.

• The central atom doesn’t have a lone pair, and the outer atoms are the same so the molecule is nonpolar.