Free Science and Math Simulations
PhET: Simulations from University of Colorado. Only HTML 5 Sims work with Chromebooks.
Concord Consortium: Simulations for all age groups with NGSS pathfinder.
CK12: Geared toward secondary but easy enough for elementary. Contains both chemistry and physics topics.
ASPIRE: University of Utah. Not sure if these have HTML 5, may need a PC for these.
Edumedia: Some are more animations but might be helpful.