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

We know that all elements have a characteristic property known as the atomic number. The atomic number of an element represents the number of electrons or protons present in the atom of the element. On the other hand, Aufbau’s Principle helps in determining the order in which the electron orbitals get filled.

Complete answer:
When we have filled all the electrons, the orbital in which the last electron is in, represents the block in which the element is placed. Now, to determine the period in which the element is placed, we need to look at the principal quantum number of the valence electron.
The principal quantum number of the valence electron of $Fe$ is $3$ . Hence, it belongs to the 3rd period. Since iron belongs to d block, its group number can be calculated by using: [number of electrons in $\left( n-1 \right)$ d subshell] $+$ (number of electrons in (n) s subshell)
Valence electrons are defined as the electrons that are present in the outermost shell of an atom. S-block elements are defined as the elements in which the last electron enters the s-orbital. The number of valence electrons of 's'-block elements is equal to the group number. P-block elements are defined as the elements in which the last electron enters the p-orbital. The number of valence electrons of 'p'-block elements is given by the equation:
Number of valence electrons $=\text{ }Group\text{ }number\text{ }-\text{ }10$
The factor of $10$ arises due to the presence of 'd'-block elements in between s-block and p-block elements.

Note:
Remember that each orbital has a fixed capacity for the maximum number of electrons accommodated; s-orbitals have the capacity of two electrons, while p orbitals have the capacity for six electrons, d orbitals have the capacity for ten electrons and f orbitals have the capacity for fourteen electrons.