1. Chemistry

2. Molecular Polarity Just like bonds can be polar because of un-equal electron distribution, molecules can be polar because of un-equal electron cloud distributions These imbalances are not the same as ion formation. How do we know when a molecule is polar?

3. Molecular Polarity Polarity in a molecules determines whether or not electrons in that molecule are distributed equally. When determining the polarity of a molecule, it is all about symmetry. Asymmetric molecules tend to be polar. Symmetric molecules are always non- polar.

4. When determining the polarity of a molecule, follow these steps: Draw the Electron Dot structure of the molecule. Using the electronegativity chart determine the difference in electronegativity for each bond. 0—0.4 = Non-polar0.5—1.7 = Polar The molecule is non-polar or polar based on the following criteria:

5. The molecule is non-polar if either:  each bond in the molecule is non-polar and there are no un-bonded electron pairs on the center atom. (example: CBr 4 )  Each C-Br bond is non-polar (ΔEN=0.3), no side of the molecule has more electron density. It is symmetrical!  each bond in the molecule has the same polarity and there are no un-bonded electron pairs on the central atom. (Example: CF 4 )  C-F bond is polar ΔEN=1.5,  But, Molecule is symmetrical

6. The molecule is polar if: each bond in the molecule is non-polar, but there are un- bonded electron pairs on the central atom. Example: NBr 3 Example: NBr 3 bonds in the molecule have different polarities and/or there are un-bonded electron pairs on the central atom. Example: CH 3 Br    

7. Molecular Polarity Summary

8. Molecule Polarity The H─Cl bond is polar. The bonding electrons are pulled toward the Cl end of the molecule. The net result is a polar molecule. 8

9. Molecule Polarity The H─O bond is polar. Both sets of bonding electrons are pulled toward the O end of the molecule. The net result is a polar molecule. 9

10. Molecule Polarity The O─C bond is polar. The bonding electrons are pulled equally toward both O ends of the molecule. The net result is a nonpolar molecule. 10 COS is linear. C and S have the same EN (2.0) but the sulfur atom is bigger than the oxygen side (more electron density),so the molecule is polar overall.

11. Polar or Non-Polar? SO 2 PF 3 BCl 3 BHF 2 Polar ( unbonded e- on center atom!) Non Polar (bonds are polar, but symmetrical) Polar – different bond polarities

12. More Molecular Polarity… Molecular 3D Models website Molecular 3D Models website