Is NO2 Polar or Nonpolar?

Answer: NO2 is polar molecule due to the presence of a lone pair of electrons whose electron-electron repulsion results in a bent structure. This unequally distributes charge within the molecule and thereby induces a permanent dipole. 

Due to the presence of only one lone pair of electrons on the central nitrogen as opposed to for example H2O with two lone pairs on the central oxygen, we find that NO2 has a larger central angle nearly 30˚ greater than H2O's "bent" structure. This combined with nitrogen dioxides electronegative oxygen atoms (3.44) on the ends decreases the dipole moment significantly. As a result NO2 has a melting point of -9.3˚C and a boiling point of 21˚C. It is soluble in less polar compounds like CCl4 and chloroform. It is said to have a "reddish-brown" color at higher temperatures.

NO2 Ball and Stick Diagram
NO2 Ball and Stick Diagram. Created with Avagadro.
How is NO2 utilized in the real world?

Nitrogen dioxide finds use in a wide variety of reactions to product for example nitric acid or nitrites. It has also found use in rocket fuels since it is a strong oxidizer having a strong affinity for electrons. However these same properties make the compound toxic to human health as the molecule will react in the respiratory system. This has been associated with an increase in asthma cases. The 2000 census indicated that half of U.S. households use gas stoves which increase threefold the risk of NO2 poisoning.

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