Question

How did the group number of s block element ?

Answer 1

Number of electronic shells is represented by period number and number of electrons present in the valence shell is represented by the group number.

For example:—

Consider chlorine having atomic number 17.

It’s electronic configuration is

1s²2s²2p⁶3s²3p⁵

it requires three electronic shells ,so it belongs to third period. It contains 7 electrons in the valence shell,hence it is placed in 7th A group of the periodic table.