how do we determine the group and period to which the element belongs if their atomic number is given?

1. First take the Atomic number of the given element. Say Cl... Atomic no. 17
2. Then calculate the electronic configuration using the atomic number 2+8+7=17 therefore the electronic configuration will be 2, 8, 7.
3.  Here we find that the no of valence electrons of element is 7 as the valence shell has 7 electrons.
4. So know we easily understand that the group is 7 because the no of valence electrons is 7.
5. Now to find the period we have to understand that the period is the number of shell the element is having therefore here chlorine has 3 shells (K-2, L-8, and M-7). So the period of the given element is 3.

Thus the position of the given element (here chlorine) is …..

Group	VII A (17th )	Valence electrons = 7
Period	3rd	Number of shells = 3