Question

What are the valence electrons? For s-block and p-block elements show that the number of valence electrons is equal to its group number.

Answer 1

Hint : Valence electrons help to calculate the common or group valence of the element. The group valence of the elements is generally either equal to the number of dots in the Lewis symbol or $8$ minus the number of dots or valence electrons.

Complete Step By Step Answer:
Valence electrons- During the formation of a molecule only the outermost electron takes part in chemical combination. The electrons present in the inner shell are well protected and are generally not involved in the overlapping or combination process. These electrons which are present in the outermost shell and participate in a chemical bond formation are known as valence electrons. For example let’s consider an element say $Be\;$ that is Beryllium. It has an atomic number $4$ . So its electronic configuration will be $1{s^2},2{s^2}$ . From this configuration we can depict that the outermost electronic configuration is $2{s^2}$ so the number of valence electrons is $2$ .
$s$ -block elements- The group $1$ and group $2$ elements which have $n{s^1}$ and $n{s^2}$ outermost electronic configuration belong to the $s$ block elements.
$p$ -block elements- Those elements which belong from group $\;13$ to $\;18$ with the outermost configuration varying from $n{s^2}n{p^1}$ to $n{s^2}n{p^6}$ .
The number of valence electron of $p$ block elements are given by the formula –
No. of valence electrons = Group number – $10\;$
For example, for a group $\;13$ the number of valence electrons will be $13-10= 3$ . Also another way to do that is, for $p$ block elements group number= $18 -$ no. of electrons required to complete an octet. Say we take an example of $N$ which has $3$ electrons in the outermost shell and requires $5$ electrons to complete its octet, therefore group no will be $18-3=15$ .
For the $s$ block element let’s take an example of , its electronic configuration is $1{s^2}2{s^1}$ . Since it has one valence electron that’s why it is placed in group $1$ . So we can conclude that for $s$ -block element, group number=number of valence electrons.

Note :
The $s$ and $p$ block elements are together called representative elements or Main group elements. According to octet rule atoms can combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons in order to complete their octet.