Question

What is the valency of nitrogen in ${ NH }_{ 3 }$?
(A). 3
(B). 4
(C). 5
(D). 1

Answer 1

- Hint: The valency determines the combining capacity of an element to form a compound. If any two elements have the same valency, then one atom of each element will combine forming the compound.

Complete step-by-step solution -

The nitrogen in ${ NH }_{ 3 }$ has three bonded hydrogen. So, the valency of nitrogen is 3. Let us know more about electronic configuration and valency in a detailed step by step method.
(1). We know that there are regions in space where there is a probability of finding electrons. The regions where the probability of finding electrons is maximum are known as the orbitals. The orbitals are named as s, p, d, and f orbitals.
(2). The capacity of every orbital is different. The maximum number of electrons that the s orbitals can have is 2. For p-orbital, the capacity of electrons is 6 while for d-orbital it is 10 and for f-orbital, it is 14.
(3). Aufbau’s Principle determines the total energy for each of the orbitals at different energy levels. It is determined by the sum of principal quantum number (n) and orbital angular momentum quantum number (l). Higher the value of n+l higher is the energy of the orbital. So, in this manner, 3d has n+l value of 3+2=5 and 4s has n+l value of 4+0=4. So, the energy of 3d > 4s.
(4). The energy levels of the orbitals are known as the principal quantum number which is denoted by a natural number. The value of ‘l’ for the s orbital is 0, while for the p orbital is 1, for d-orbital, it is 2 and for f orbital, it is 3. The electrons always get filled from lower energy orbital to higher energy orbital.
(5). According to Aufbau’s Principle we can arrange the orbitals according their energy as:
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p
The number of electrons in each orbital is denoted by using superscript number to its orbital name. For example - ${ 4s }^{ 2 }{ 3d }^{ 5 }$ etc.
(6). The atomic number of Nitrogen is 7. We can write the electronic configuration using the above principle as ${ 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 3 }$.
(7). As we know the capacity of p orbital is 6 and there are 3 electrons required for nitrogen to fulfil the capacity of p orbital, it will form covalent 3 bonds to get 3 extra shared electrons to fulfil its p orbital.
(8). As we know the valency is the capacity to combine with other elements since nitrogen can bond with 3 elements, its valency is 3. Therefore, also in ${ NH }_{ 3 }$, the valency of nitrogen is 3.

Note: The element can combine with the same element in a double or triple bond. Each bond will count as one. In dinitrogen ( ${ N }_{ 2 }$ ) Nitrogen has a triple bond with another nitrogen. Here also it has a valency of 3. So, don’t get confused between them.