If you're seeing this message, it means we're having trouble loading external resources on our website. Show If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. The two main classes of molecules are polar molecules and nonpolar molecules. Some molecules are clearly polar or nonpolar, while others fall somewhere on the spectrum between two classes. Here's a look at what polar and nonpolar mean, how to predict whether a molecule will be one or the other, and examples of representative compounds. Key Takeaways: Polar and Nonpolar
Polar MoleculesPolar molecules occur when two atoms do not share electrons equally in a covalent bond. A dipole forms, with part of the molecule carrying a slight positive charge and the other part carrying a slight negative charge. This happens when there is a difference between the electronegativity values of each atom. An extreme difference forms an ionic bond, while a lesser difference forms a polar covalent bond. Fortunately, you can look up electronegativity on a table to predict whether or not atoms are likely to form polar covalent bonds. If the electronegativity difference between the two atoms is between 0.5 and 2.0, the atoms form a polar covalent bond. If the electronegativity difference between the atoms is greater than 2.0, the bond is ionic. Ionic compounds are extremely polar molecules. Examples of polar molecules include:
Note ionic compounds, such as sodium chloride (NaCl), are polar. However, most of the time when people talk about "polar molecules" they mean "polar covalent molecules" and not all types of compounds with polarity! When referring to compound polarity, it's best to avoid confusion and call them nonpolar, polar covalent, and ionic. Nonpolar MoleculesWhen molecules share electrons equally in a covalent bond there is no net electrical charge across the molecule. In a nonpolar covalent bond, the electrons are evenly distributed. You can predict nonpolar molecules will form when atoms have the same or similar electronegativity. In general, if the electronegativity difference between two atoms is less than 0.5, the bond is considered nonpolar, even though the only truly nonpolar molecules are those formed with identical atoms. Nonpolar molecules also form when atoms sharing a polar bond arrange such that the electric charges cancel each other out. Examples of nonpolar molecules include:
Polarity and Mixing SolutionsIf you know the polarity of molecules, you can predict whether or not they will mix together to form chemical solutions. The general rule is that "like dissolves like", which means polar molecules will dissolve into other polar liquids and nonpolar molecules will dissolve into nonpolar liquids. This is why oil and water don't mix: oil is nonpolar while water is polar. It's helpful to know which compounds are intermediate between polar and nonpolar because you can use them as an intermediate to dissolve a chemical into one it wouldn't mix with otherwise. For example, if you want to mix an ionic compound or polar compound in an organic solvent, you may be able to dissolve it in ethanol (polar, but not by a lot). Then, you can dissolve the ethanol solution into an organic solvent, such as xylene. Sources
Cite this Article Format mla apa chicagoYour Citation Helmenstine, Anne Marie, Ph.D. "Examples of Polar and Nonpolar Molecules." ThoughtCo. https://www.thoughtco.com/examples-of-polar-and-nonpolar-molecules-608516 (accessed January 4, 2023). How can you tell if a diagram is polar or nonpolar?If the arrangement is symmetrical and the arrows are of equal length, the molecule is nonpolar.. If the arrows are of different lengths, and if they do not balance each other, the molecule is polar.. If the arrangement is asymmetrical, the molecule is polar.. |