Chemistry Trumps Top Card Game plays like War, except you compare atomic weights, dangerousness, usefulness, melting point, year discovered of particular elements. Our cards came today and we played for two straight hours! Easy enough for younger kids, they work like flash cards. The only drawback is that there are only 32 cards.
While you're there, check out the other webelements products. The "Periodic Noir" t shirt features the periodic table--the radioactive elements glow in the dark! Youth size large to adult XL
(I get no kickback for recommending these products. We're just having such a good time with them, I thought I'd pass them on.)