One of the earliest topics encountered by students of chemistry is atomic theory (the structure of the atom). The Building Atoms, Ions and Isotopes HD Lite app is a free app by Carolina Biological Supply that provides students an interactive tool for learning about atom structure. Students are given an atomic element (complete with atomic and mass numbers) and must then attempt to successfully recreate the element by specifying the number of electrons, protons, and neutrons to add to their “atom” on the screen. The app also includes a brief introduction to the history of atomic theory. Unfortunately, as this is the “lite” version, it is limited to building atoms; if you wish to actually build ions and isotopes as the app’s name suggests, it will cost you $2.99.