4. Electron Sharing and      Covalent Bonds  
     Nitrogen and Ammonia

The electronegativities of H and N are appreciably different: 2.1 and 3.0, respectively. The three H-N bonds therefore are partly ionic, or polar, with the electrons held more tightly by N than by H. The charge in the molecule also is asymmetrical, because of the extra electron pair at the apex of the pyramid and three H atoms with an electron deficiency at the base. This means that there actually exists a small separation of charge on the molecule: The apex is slightly negative and the base is slightly positive. Thus the molecule is said to have a tiny dipole.

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