Question

According to Hund's rule, the nitrogen atom has __ unpaired electrons.
(a) 0
(b) 1
(c) 2
(d) 3

Answer 1

The atomic number of Nitrogen is 7 and the electrons are filled according to the increasing order of their energy.
The increasing order of orbitals in energy is 1s,2s,2p,3s,3p,4s,3d,4p etc.

Complete step-by-step answer: In the question, it is asked that taking into consideration of Hund's rule,how many unpaired electrons are present in a nitrogen atom.
Nitrogen is the element with atomic number 7 and hence there are a total of seven electrons, 7 protons and 7 neutrons in nitrogen atom.It has a mass number of 14amu.
The seven electrons present in N are filled in various orbitals in the increasing order of their energy.
The increasing order of energy of orbitals are: $1s<2s<2p<3s<3p<4s<3d<4p$…
Now let us write the electronic configuration of N atoms.
$Electronic\,configuration\,of\,N=1{{s}^{2}}2{{s}^{2}}2{{p}^{3}}$
According to Hund's rule, every orbitals should be singly filled first before they get doubly filled.The Hund's rule is applicable for the degenerate orbitals also.It also states that the singly filled electrons in all the electrons will have the same spin.
And we know that there are three orbitals associated with the p-subshells, ${{p}_{x,}}{{p}_{y\,}}$and ${{p}_{z}}$
And in N atoms four electrons are occupied by 1s and 2s orbitals and the remaining three are singly filled in the three orbitals present in the p subshell.
Therefore there are three unpaired electrons present in a Nitrogen atom instead of six electrons.
And N could bond with three other atoms by accommodating three electrons in their p orbitals.

Therefore the correct answer for the given question is option (d).

Note: Electrons are filled in orbitals by following rules like Afbau principle, Hund's rule and Pauli's exclusion principle.
When two atoms are filled in the same orbital or paired up in an orbital, then the total spin will be zero and is called as diamagnetic electrons and the substance with zero spin is called as diamagnetic substances.
The atoms which have unpaired electrons will have a net spin and are called as paramagnetic atoms and the substances with paramagnetic atoms are called as paramagnetic substances.