Via StumbleUpon, I came across this nice collection of chemistry videos at listverse.com: The Top 10 Amazing Chemical Reactions. If you want to see chemicals acting in very ‘unnatural’ ways, take a gander.
My favorite is the sulfur hexafluoride, an invisible gas over 5 times heavier than air. Because of this, it can be held in an open container and have lightweight objects floated on top of it. On a more serious note, it reminded me of another gas which is heavier than air: carbon dioxide. In 1986, Lake Nyos in Cameroon released a massive amount of carbon dioxide that had been suspended in solution at the lake’s bottom, evidently much like a can of soda bubbles over when pressure is released. The carbon dioxide hugged the ground and ended up smothering and poisoning 1800 people in the lake’s vicinity. (Cattle were not spared from the effects, either.) Currently, a French-Cameroon team is working on ‘degassing‘ the lakes by venting the gas from the lake bottom.
Skulls in the Stars 
Those reactions look like the most fun you can have with chemistry without blowing anything up.
Exercise: If you fill a balloon with sulfur hexafluoride, it will gradually inflate more and more, until it pops. Why?
Blake: Ouch! You’re hitting me in my weakest spot: right in the stat. mech.! I’m not completely sure, but I would venture a guess that the s-h can’t readily leak out of the balloon, while plain old air is ‘leaking’ into the balloon, to equalize the amount of air inside and out. Am I close?