# Why do nitrogen show tetra covalency in some cases ?

Mar 14, 2016

Consider the neutral ammonia molecule, $N {H}_{3}$. Is this capable of further reaction?

#### Explanation:

The ammonia molecule is a neutral species; nevertheless it can undergo acid-base reaction by virtue of the lone pair on nitrogen:

NH_3 + H_2O rightleftharpoons NH_4^+ + ""^(-)OH

We say that the nitrogen atom has become quaternized; i.e. the lone pair has formed a coordinate covalent bond to a proton (the nitrogen now bears a formal positive charge because it is associated with 6 electrons [2 inner core and 4 from the $N - H$ bonds] rather than 7 electrons.) Likewise, there are 9 electrons around oxygen (including core), and, therefore, this bears a negative charge.

Of course we can have tetra-alkyl ammonium salts as well, $N {R}_{4}^{+}$.

The nitrogen containing species is now a quaternary ammonium salt, with a formal positive charge on nitrogen.