Why is NH3 (Ammonia) Polar?
Ammonia is considered as polar as it has one lone pair of electrons on the nitrogen atom. Any molecule in order to be determined as polar has to follow certain steps. These steps will confirm whether the molecule is polar or non-polar. This procedure will also clarify why ammonia is Polar. Firstly the Lewis structure of the molecule should be designed. Then the shape of the molecule must be finalized using valence shell electron pair repulsion theory (VSEPRT). The next step is to find out the polar bonds in the molecule.
To identify the polar bonds in the molecule, it is essential to determine the actual electro-negativities of the two atoms forming that bond. The relative electro-negativities also are necessary to determine the polarity of the molecule. The direction of the polarity for the bond also should be determined. The shared electrons in the molecule are dragged strongly towards it by the most electronegative atom in the molecule. Due to this strong attraction of the electron pair towards the most electronegative atom, it attains negative charge. The other atom will have slightly positive charge. Thus, the molecule becomes Polar with partial positive and partial negative charges on the respective atoms. Now, the bond formed is called polar and it has dipole-dipole moment. The net dipole moment is calculated from all the individual dipole moments.
The above steps involved in determining the polarity of the molecule can be applied to ammonia also. Firstly, the Lewis structure of ammonia shows the free lone pair of electrons on nitrogen atom. The VSEPR theory gives the shape of ammonia as pyramidal. Nitrogen is more electronegative than hydrogen and hence electrons are nearer to nitrogen. The dipole moment is calculated and the direction of polarity is also determined for ammonia. The negative polarity is determined towards the direction of nitrogen. The positive charge is determined to be at the center of the three hydrogen atoms. This is the reason why ammonia is polar.