Is NCl3 Polar or Nonpolar?

Answer: NCl3 is a polar molecule due the presence of a lone pair of electrons. This leads to electron-electron repulsion which results in a bent structure, thereby causing an unequal distribution of charge within the molecule and creating a permanent dipole.  

Since there are three quite electronegative chlorines (3.16) the impact of the lone-pair electron is less and therefore the dipole moment is weaker than a molecule such as ammonia (NH3). This is why NCl3 has a lower melting and boiling point (-40˚C and 71˚C, respectively) than ammonia. In fact, NCl3 can be combined with water to produce NH3 and hypochlorous acid.

To learn more about a similar molecule (ammonia), feel free to check out the following articles regarding the polarity and the Lewis Dot Structure for NH3.

NCl3 Ball and Stick Model
NCl3 Ball and Stick Model. Created with MolView.
Where is NCl3 found in the real world?

The molecule is most often formed as a byproduct from reactions involving ammonia-derivatives and chlorine. One of the most common places where NCl3 is formed is at swimming pools. The liquid formed is a "yellow" color and is responsible for the distinctive chlorine smell found at chlorinated swimming pools. The large number of halides makes the molecule unstable being sensitive to many different forms of energy input which typically lead to an explosion.