I think i have seen u more than twice that u r asking about electronic configuration..so now let me explain see koi bhi atom hota h usme electrons as well as protons and neutrons hote h and tum ye bhi jaante hoge ki saare electrons atom ke nucleus ke chaaro traf ek fixed path par revolve krte rehte h to ab saare electrons ek hi path pe revolve to nhii na kr sakte h just suppose agar saare planets ek hi path par sun ka revolution krne lage to kyaa hoga same case is with these electrons.so we have to put electrons on their paths jise shell yaa orbit bhi kehte h to nucleus ki taraf se aage ki or ham shells ka naming krte h and they r K L M N and so on or 1 2 3 4 and so on..but kuchh rules h that we have to follow when we put electrons in different shells like1.an orbit or shell can not keep more than 2n^2 electrons.where n is the position of the shell(k posit is 1,M position is 2,N position is 3 and so on..)2.outermost orbit can not keep more than 8 electrons..3.orbit just before the outermost orbit or second outermost orbit cant keep more than 18 electrons..that's all now take an example atomic no of oxygen is 8 means it has 8 electrons..so now we put these electrons shell wise.okey see Kshell-2n^2 electrons=2×1^2=2.. L shell=6 here we cant keep on formula coz if we put then 2n^2 electrons =2×2^2=2×4=8electrons and if we add the electrons of K shell which is 2 then it becomes 8+2=10 electrons but the electrons present in it is only 8 so,its electronic configuration will be 2,6...okey..sorry bro aur jyaada examples nhii de sakta coz my fingers are saying me not to TYPE any more...