3.3 Polar Bonds and Polar Molecules
Remember:
-the polarity of a bond is determined by calculating ∆EN
-When a bond is polar, electrons spend more time closer to the element with the highest
electronegativity.
-A polar bond has poles. The least electronegative atom appears to have "lost" electrons (denoted as
ɗ+) and the most electronegative atom appears to have "gained" electrons (denoted as ɗ-)
Example HCl ∆EN=Cl - H
=3.2-2.2
=1.0 polar covalent bond
positive pole
ɗ+
ɗ-
negative pole
H - Cl
Molecular polarity
To determine the polarity of an entire molecule you must consider:
1. The bond polarity
2. The 3D shape of the molecule
-lone pairs will bend bonds and make molecules asymmetrical ex. H2O
Determining Molecule Polarity Steps:
1. Draw the lewis structure of the molecule. Remember: lone pairs bend bonds down
2. Determine the bond polarity of each bond (∆EN)
3. For the polar bonds, indicate the partial charges with ɗ+ for the element that is least electronegative
and ɗ- for the element that is most electronegative.
4. One polar bond = polar molecule (example HCl)
More than one polar bond = if asymmetrical then it is a polar molecule (example H2O and NH3)
= if symmetrical then its a non-polar molecule (example SiCl4 and CO2)
Only non-polar bonds = non-polar molecule (example F2)
Examples:
1. CO
2. NF3
3. OCl2
4. CHCl3
5. O2
6. CH4