Front. Knitted for my husband around 1993 from Lion Brand Wool Ease. Worked without a chart, directly from an old chemistry textbook (it's missing some of the older elements). This took me 10 days to knit. The entire sweater was done freehand, without calculating ahead of time except to make sure that the Period Table would fit on the front and back. The body is knitted in the round and the sleeves are steeked.
Blogged at apinnick.wordpress.com/2009/08/05/periodic-table-sweater/. Note: you can download a PDF of the pattern at that link.