9.3. Polarity in Chemical Bonds http://www.ck12.org
FIGURE 9.14
The hydrogen fluoride molecule. The blue
region represents an area of partial posi-
tive charge, the white area is electrically
neutral, and the pink area is a zone of
partial negative charge.Classifying Chemical Bonds
How do we know if a specific pair of electrons will form a covalent bond or an ionic one? Electronegativity data
turns out to be a fairly useful tool to make these predictions. Although there is no clear line between a polar covalent
bond and an ionic one, we can define some general guidelines:
- Purenonpolar covalent bondsexist only between two identical atoms. The H-H bond would be 100%
covalent, because there is no difference in electronegativity between the two atoms. - If the electronegativity difference between the two atoms is 0.4 or less, the polarity of the bond is very minimal,
and neither atom takes on a significant partial charge. For example, the C-H bond (an electronegativity
difference of 0.4) is essentially non-polar. - When the difference in electronegativity is between 0.5-1.6, the electrons are still shared (the bond is covalent),
but it is significantly polarized. We refer to these aspolar covalent bonds. - Ionic bonds tend to form between atoms for which the electronegativity differences are 2.0 and above. In
general, ionic bonds between two atoms require one metal and one nonmetal.
Lesson Summary
- Electronegativity is the tendency of an atom to draw shared electrons towards itself.
- Polar bonds contain atoms that possess either a partial positive or a partial negative charge.
- Electronegativity differences can be used to predict the extent to which a particular chemical bond is polarized.