Question

How many unpaired electrons are there in $N{{i}^{2+}}$?

Answer 1

Nickel is a chemical element represented by the symbol Ni. It is silvery white in color, lustrous in nature, hard and brittle transition element. Nickel is present in the fourth period in the periodic table and refers as an important nutrient for the body.

Complete answer:
Unpaired electrons can be defined as an electron which occupies an orbital of an atom in single form rather than present as a part of the electron pair. Compounds in which electrons are not paired are known as unpaired electrons and these are very reactive in nature.
Atomic number of nickel is 28 now to find out the number of unpaired electrons we have to know about the electronic configuration of an atom. Electronic configuration of an atom gives us the idea about the distribution of electrons and electronic configuration of nickel can be written as: $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}3{{d}^{8}}$, but in the given question we have to find unpaired electrons of nickel having oxidation state +2. The oxidation state +2 corresponds to the losing of 2 electrons so the electronic configuration can be shown as $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}3{{d}^{6}}$ this corresponds that there are 6 electrons in d-orbitals we know that d-orbital have 5 degenerate orbitals so 6 corresponds one is already paired in this so there are 4 unpaired electrons.
Thus we can say that 4 unpaired electrons are there in $N{{i}^{2+}}$.

Note:
Each atomic orbital of an electron has capacity to contain two electrons which are of opposite spin value i.e. if one electron is in the state of clockwise then another will be in anticlockwise state and this was explained by Pauli exclusion principle.