Describe how chemical energy is related to chemical change.

Different isotopes indicate that an element will have different numbers of

Can someone me with questions 15 to 17 plz.

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!