What's the difference between the molecular structures of hexavalent chromium and trivalent chromium (other than the number of bonds, I get that much) that leads to hexavalent chromium releasing harmful chemicals? Is it something left over after the chroming process that's not left over with trivalent chromium?

Also, more LOLz for B.I.L.F. I like Natalie Dee and Toothpaste for Dinner a lot.