Question

What is the valency of Nitrogen in $N{{H}_{3}}$ ?

Answer 1

Hint: Remember that the electronic configuration of Nitrogen is \[1{{s}^{2}}2{{s}^{2}}2{{p}^{3}}\]. With this in mind along with what the definition of valency really is, try and work the answer to this question out.

Step-by-Step Solution:
Let us first establish what the terms valency means before moving on to answer this question.
Valency is the measure of the combining capacity of atoms or molecules. Therefore, it is the capacity of an atom of a single element to react and combine with particular numbers of atoms of another element. The valency of an atom is equal to the valence electrons i.e. the number of electrons in its outermost shell, if it is 4 or less. If it is more than 4, the valency is equal to 8 minus the number of electrons in the outer shell.
In other words, it is the number of electrons an atom of an element can gain, lose or share. Example: Magnesium has electronic configuration 2,8,2. Therefore its valency is 2 due to the presence of 2 electrons in its valence shell.
Let us now apply this same logic to Nitrogen in Ammonia.
As observed in Nitrogen, its valence shell contains 5 electrons making its maximum possible valency 5. Now the number of electrons shared by nitrogen in ammonia is 3 only, one with each of the 3 hydrogen atoms while the remaining two electrons remain as a lone pair. Since the number of electrons shared by nitrogen is 3, hence the valency of Nitrogen in ammonia is 3.

Note: Nitrogen is found to have either 3 or 5 valence electrons and lies at the top of Group 15 on the periodic table. It can have either 3 or 5 valence electrons because it can bond in the outer 2p and 2s orbitals.