re:117 hasn't got the Eight connection implied in the word
However the halogens are the 17th column in the PT, and 7+1 is a far better way of referring to 8 as proper fans will know. 7b is also OK.
However the halogens are the 17th column in the PT, and 7+1 is a far better way of referring to 8 as proper fans will know. 7b is also OK.