Why is ammonia considered a polar molecule?

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Difference in molecular structure between ammonia/amines and quaternary ammonium ions — ammonia Ammonia and amines have a slightly flattened trigonal pyramidal shape with a lone pair of electrons above the nitrogen. In quaternary ammonium ions, this area is occupied by a fourth substituent.

Ammonia is considered a polar molecule primarily due to its trigonal pyramidal molecular geometry.1

In this structure, the nitrogen atom is bonded to three hydrogen atoms, and it also retains an unshared pair of electrons. Because the nitrogen atom is more electronegative than the hydrogen atoms, the covalent bonds between them are polar.123

The asymmetric arrangement of these polar bonds, combined with the presence of the lone electron pair, prevents the bond dipoles from canceling each other out. This results in a net molecular dipole, making the ammonia molecule polar. This polarity is further significant because it facilitates strong intermolecular hydrogen bonding, which influences the physical properties of the compound.1