The kids novels by the Hawkings are great at that age, even if he's moving out of physics: (https://www.amazon.com/Georges-Secret-Key-Paperback-Collection/dp/1481484346/ref=sr_1_2?ie=UTF8&qid=1473947640&sr=8-2&keywords=George%27s+Secret+Key+to+the+Universe)
A real molecule set is a ridiculously expensive but awesome thing. My DS was in heaven when we pulled out my old university kit. Especially since he was doing some science experiments with materials simple enough that he could build them at all stages. (Hot ice, for example, is great for this, and way cool to play with). Even with a standard (small) kit, you have enough pieces to build the vinegar and baking soda molecules, and create all the steps of breaking up, evaporating off, re-combining, etc. Mr. Social Anxiety morphed into super-excited Showman Extraordinaire demonstrating this to his (admittedly somewhat bewildered) class in grade 2. (Here's an example, but there's tons of web sites about this:
http://chemistry.about.com/od/homeexperiments/a/make-hot-ice-sodium-acetate.htm)
