Predicting Molecule Polarity
- This classification table gives a good general understanding of predicting molecular dipole of some general molecular structures. However, one should not interpret it literally:
| Formula | Description | Example | |
| Polar | AB | Linear Molecules | CO |
|---|---|---|---|
| HAx | Molecules with a single H | HF | |
| AxOH | Molecules with an OH at one end | C2H5OH | |
| OxAy | Molecules with an O at one end | H2O | |
| NxAy | Molecules with an N at one end | NH3 | |
| Nonpolar | A2 | Diatomic molecules of the same element | O2 |
| CxAy | Most carbon compounds | CO2 |
- Determining the point group is a useful way to predict polarity of a molecule. In general, a molecule will not possess dipole moment, if the individual bond dipole moments of the molecule cancel each other out. This is because dipole moments are euclidean vector quantities with magnitude and direction, and a two equal vectors who oppose each other will cancel out.
Any molecule with an centre of inversion ( "i" ) or a horizontal mirror plane ( "σh ") will not possess dipole moments. Likewise, a molecule with more than one Cn axis will not possess dipole moment because dipole moments cannot lie in more than one dimension. As a consequence of that constraint, all molecules with D symmetry (Schönflies notation) will, therefore, not have dipole moment because, by definition, D point groups have two or multiple Cn axis.
Since C1, Cs,C∞h Cn and Cnv point groups do not have a centre of inversion, horizontal mirror planes or multiple Cn axis, molecules in one of those point groups will have dipole moment.
Read more about this topic: Chemical Polarity
Famous quotes containing the words predicting, molecule and/or polarity:
“To regard one’s immortality as an exchange of matter is as strange as predicting the future of a violin case once the expensive violin it held has broken and lost its worth.”
—Anton Pavlovich Chekhov (1860–1904)
“We can come up with a working definition of life, which is what we did for the Viking mission to Mars. We said we could think in terms of a large molecule made up of carbon compounds that can replicate, or make copies of itself, and metabolize food and energy. So that’s the thought: macrocolecule, metabolism, replication.”
—Cyril Ponnamperuma (b. 1923)
“The same polarity of the male and female principle exists in nature; not only, as is obvious in animals and plants, but in the polarity of the two fundamental functions, that of receiving and penetrating. It is the polarity of earth and rain, of the river and the ocean, of night and day, of darkness and light, of matter and spirit.”
—Erich Fromm (1900–1980)