ernest rutherford atomic model included a nucleus comprised of positive particles called protons. later james chadwick discovered neutrons. how did chadwicks discovery change the atomic model

I'm learning about the periodic tables and what each subject's configuration is. for example, hydrogen is 1s^1, but i don't understand how you get that. can someone me understand how to figure out how to figure this out? sorry if the question makes no sense, but it would really a lot if you could me understand! you so much if you can!