FINDING GROUP AND PERIOD NUMBERS

We know that the elements are arranged in the order of increasing atomic numbers. Elements which have the same electron configuration in their valence shells are placed in the same group. 

Knowing this, the place of any element in the periodic table can be easily found when its atomic number or the number of the electrons of the neutral atom or the electron configuration in ground state is known. 

In order to find the group and period number of any atom, the ground state electron configuration is written first. Then the following points are taken into consideration. 

The biggest principal quantum number (shell number) of any atom shows the period number of that atom. 

If the electron configuration of an atom ends with s or p orbitals, this atom belongs to group A and the group number is determined by adding the number of electrons in the valence shell. 

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