to find electronic configuration , group number and period number of an element from its atomic number
potassium atomic number 19

Explanation

Its electronic configuaration is :
` 1s^2 | 2s^1 2p^6 | 3s^4 3p^4 | 4s ^2 = ( 2,8,8,1)`
this means it contains 2 electrons In K - shell , 8 electrons in L shell 8 electrons in M shell and 1 electron in N shell .
Its period number = No of shells =4
Its group number = no. of valence electrons = 1
[If number of valence electrons is 1 or 2 group number = no of valence electrons .