Question

If Hund's rule is not applicable then how many unpaired electrons are present in NO molecule?

Answer 1

Hint: Hund's rule relates to the filling of electrons in the orbitals during the formation of molecules. The number of singly occupied orbitals or unpaired electrons will decrease if Hund’s rule is not applied.


Complete step by step solution:
 Hund's rule is also called rule of maximum multiplicity. According to this rule all the orbitals shall be singly filled before the starting of pair formation. The orbitals which this rule takes into consideration have the same energy such as all the three orbitals of p subshell, all the five orbitals of d subshell, all the 7 orbitals in subshell, and so on. This rule was formalized or given by Fredrick Hund and is widely applicable in Quantum chemistry and also spectroscopy. For NO molecule,

   Nitrogen -7(atomic number)
   Oxygen- 8(atomic number)

\[N(7):\,1{{s}^{2}}\,2{{s}^{2}}\,2{{p}^{3}}\]⇒unpaired electrons-3
\[o(8):\,1{{s}^{2}}\,2{{s}^{2}}\,2{{p}^{4}}\]⇒unpaired electrons-2

Total unpaired electrons if Hund’s rule is followed is 5.
The number of unpaired electrons if this rule is applied is 5 but if this rule is not applicable, in all the orbitals pairing of electrons will start. As a result, the feeling will be such that,
N:unpaired electrons-1
O: unpaired electrons-0
total unpaired electrons if Hund’s rule is not followed is 1.
Hence only one electron will be unpaired if this rule is not followed or is not applicable in a NO molecule. Out of total 15 electrons of both nitrogen and oxygen 14 will get paired and one will remain unpaired.

Note: The hybridization of the NO molecule will change if the Hund’s rule is not followed.