Question

What is the valency of manganese in $MnO_2$ ?

Answer 1

Hint : Valency indicates the bonding capacity of any element in the given compound. Manganese is a chemical element with the symbol Mn and atomic number is 25.Manganese is a transition element so it can have more than one valence state.

Complete step by step answer
In this question, $\text{MnO}2$ one molecule of manganese and two molecules of oxygen are joined to form this compound.
$\text{Mn}+{{\text{O}}_{2}}\to \text{Mn}{{\text{O}}_{2}}$
Let valency of manganese (Mn) be “x”
$\text{Mn}+{{\text{O}}_{2}}\to \text{Mn}{{\text{O}}_{2}}$
In this compound i.e. $MnO2$ , each oxygen atom carries $-2$ charge. So total charge on oxygen will be $-4$ . To balance the negative charge on the oxygen (O) atom there should be the same positive charge on the Mn atom to make a neutral compound. . Due to its different electronic configurations this element shows variable valency. Sometimes an atom of element can lose more electrons than present in its valence shell.
$\text{Mn}+{{\text{O}}_{2}}\to \text{Mn}{{\text{O}}_{2}}$
$x+\left( -4 \right)=0$
$x=\left( +4 \right)$
Therefore the valency of Mn is $+4$ in $\text{Mn}{{\text{O}}_{2}}$ molecule or we can say it is manganese (IV) oxide.
As we know that manganese is a transition metal, it can have more than one valence state. Its electronic configuration is $\left[ \text{Ar} \right]3{{\text{d}}^{5}}4{{\text{s}}^{2}}$ .it is not found as a free element in nature. Due to its different electronic configurations this element shows variable valency. Sometimes an atom of element can lose more electrons than present in its valence shell. Structure of manganese oxide is O = Mn =O.
The valency of manganese in $\text{Mn}{{\text{O}}_{2}}$ is $+4$ .

Note
Electrons exist in orbits around an atomic nucleus. The higher the orbit number, the greater the distance of the electrons from the nucleus. Atoms try to achieve a stable state similar to that of the noble gases or the inert elements in their outermost orbit by accepting or donating electrons. This property is called the atom’s valency. Some elements differ in their capacity to combine with other elements depending on the nature of the reaction; this property is called variable valency.