Building Atoms, Ions, and Isotopes HD Lite App for iPad
'With the Building Atoms, Ions, and Isotopes app, explore the composition of the elements. Build atoms, ions, and isotopes by selecting appropriate numbers of protons, neutrons, and electrons. For reference, this app also includes atomic theory information and a periodic table that is interactive in the iPad version.
*Lite version only includes Build an Atom and Atomic Theory History Features'
This is a free app