Question

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

Answer 1

Electrons present in the outermost shell of the atom of an element are called valence electrons.

3Li is an s-block element and its electronic configuration is 1s²2s¹. Since it has one valence electron, it is placed in group 1.

Therefore, for s-block elements, group number = number of valence electrons.

However, for p-block elements, group number = 18 – number of electrons required to attain complete octet.

7N is a p-block element and its electronic configuration is 1s²2s²2p³. Since it has five electrons in its valence shell, it is short of three electrons to complete its octet.

Therefore, its group number = 18 – 3 = 15.