If an element is in group 1 and 7 then this means the respectively they have one electron in the outer shell and they have 7 electrons on the outer shell. A full outer shell concludes of 8 electrons. And to make these elements stable it must bind together (either metallically ionically or covalently) and share each other’s electron. So the first element needs to give off its one extra electron so all of its outer shells can be full and the second element must gain an electron so it can fill up its outer shell and become stable. And when this happens the element in group 1 will become a positive ion my +1 and the element in group 7 will become a negative ion by -1
