In my high school chemistry class, a unit we cover is that of atomic structure. In particular, given an elements symbol, mass number, atomic number, and charge, the objective would be for the student to determine the atoms number of protons, neutrons, and electrons. I have several apps/program suggestions that can be useful for this purpose.
A few weeks ago, I presented at ChemEd 2013 "Flipping with Chemistry Apps". One app that I use in my HS chemistry class on the iPad is the app Building Atoms, Ions, and Isotopes HD Lite.