Question

The valency of sodium is 1. The valency of chlorine is 1. Write the formula of sodium chloride.

Answer 1

Hint: valency of a sodium atom is $\text{ +1 }$ and chlorine is $-1$.sodium donates its outermost electron and chlorine atom gains the same electron to complete its octet. $\text{ N}{\text{a}}^{\text{+ }}$ and $\text{ C}{\text{l}}^{-}$ ions combine to form an ionic compound.

Complete Solution :
The valency of an element is a combining capacity of an atom .This is considered as the number of bonds an atom can form to attain stability.
The valency of an atom depends on the number of electrons present in the outermost shell.
The electronic configuration of sodium is as shown below:
$\text{ Na = 1}{\text{s}}^{\text{2}}\text{ 2}{\text{s}}^{\text{2}}\text{ 2}{\text{p}}^{\text{6}}\text{ 3}{\text{s}}^{\text{1 }}$
Sodium atom loses its $\text{ 3s }$ electron to attain the nearest noble gas configuration of $\text{ Ne }$ . Since sodium has only one electron in the outermost shell which takes part in the bonding its valency is $\text{ +1 }$ .
Similarly, the electronic configuration of chlorine is as shown below,
$\text{ Cl = 1}{\text{s}}^{\text{2}}\text{ 2}{\text{s}}^{\text{2}}\text{ 2}{\text{p}}^{\text{6}}\text{ 3}{\text{s}}^{\text{2 }}3{\text{p}}^{\text{5}}$
Chlorine atoms can accept the electron in $\text{ 3p }$ orbital to attain the nearest noble gas configuration of $\text{ Ar }$ . Chlorine has 7 valence electrons. It requires one more electron to complete its octet. The valency of the chlorine atom is $-1$ .
Sodium loses its one electron and completes its octet and chlorine accepts this electron. They are bonded through the ionic bond.
$\text{ Na }\to \text{ N}{\text{a}}^{\text{+}}\text{ + }{e}^{-}$
Chlorine accepts electrons as follows:
$\text{Cl + }{e}^{-}\to \text{ C}{\text{l}}^{-}$
The ionic reaction between the sodium metal and chlorine is as shown below,
$\text{ N}{\text{a}}^{\text{+}}\text{ + C}{\text{l}}^{-}\to \text{ NaCl }$
The chemical formula of sodium chloride is $\text{ NaCl }$ .

Note: Note that the compounds do not have a valency. Thus sodium chloride $\text{ NaCl }$does not exhibit a valency. But we can determine the valencies of the sodium and chlorine atom, it is 1 for both. Remember that this method is based on the octet rule. In this case, the octet rule is followed by an element and combine to attain a stable configuration.