Question

What do you understand by the following terms valency, valence electrons and valence shell?

Answer 1

We need to know that by using valency we can explain the reacting capacity of an atom with the other atom. And we can depict the property of an element by using the valency. And the valency does not contain any positive or negative sign. These valency, valence electrons and valence shells can be explained by using the outer electronic configuration of an atom or molecule. And the valency will help to predict the molecular formula of the compound.

Complete answer:
As we know, the number of unpaired electrons present in the outermost hell is known as valency. Consider the case of oxygen. The electronic configuration of oxygen is, $1{s^2}2{s^2}2{p^4}$. Here, the outermost orbital contains six electrons and $2s$ orbital is completely filled. The maximum electron contained in p – orbital is equal to six. But here the p orbital contains only four electrons. Two are unpaired. Therefore the valency of oxygen is equal to two.
The number of electrons present in the outermost orbital or shell is known as valence electron. The gold is a chemical element having the atomic number $79$ with symbol, $'Au'$. The electronic configuration of gold can be written as, $\left[ {Xe} \right]4{f^{14}}5{d^{10}}6{s^1}$ here, the five – d orbital is completely filled. And the maximum number of electrons occupied in s – orbital is equal to two. Here, the outermost shell is $6s$. Hence, the valence electron of gold is equal to one.
And the valence shells are the pair of orbitals which are ready to accept the electrons energetically and to form the chemical bonds. For example, the number of valence shells present in carbon is equal to four and nitrogen is equal to five.

Note:
We have to remember that the valency is the number of unpaired electrons present in an outermost orbital of an atom present in the element. But the valence electron is the number of valence electrons present in the outermost shell. The valence electron can be used for the formation of chemical bonds. And the main role of the valence electron is to transfer the electron between the atom by losing or gaining in the process.