▀▄OUT OF SIGHT WE STRIKE, THE BATTLE IS OVER▄▀
▄▀▄▀▄▀▄▀▄▀▄▀GHOSTS OF 0NYX▀▄▀▄▀▄▀▄▀▄▀▄
Think about it.
One of the missing elements is number 117 (number 117!!!), it still hasn't been found even though it exists (much like halo 3 ending), and then the column that the element would be under would be Halogens....doesn't get any more obvious than that to me. Oh and the other column is Noble Gases which we need to survive and there are 6 of them. i think halo gets some references to the periodic table