A very quick update. Per feedback from various sources, I decided it was time to add pinch zoom functionality to the small screen version of the app. Not only did people directly comment that this would be a more intuitive approach, I had also observed people naturally attempting the pinch gesture to zoom in and out of a molecule while using a phone to view the app.
Some tweaking was done to modify the sensitivity of reacting to the pinch gesture as well as to occlude any panning activity from being performed simultaneously. An update was also made to not automatically re-center the molecule upon a zoom in or zoom out. Finally, the plus and minus icons were removed from the small screen version of the app as they are no longer needed for the zoom functionality. This removal has allowed more precious small screen real estate to be used.
Controls: A pinch in gesture will now cause a zoom in effect on the molecule. Similarly, a pinch out gesture will cause a zoom out. This was primarily designed to be effective on small screen devices, but other devices that register touch events, such as a laptop with a touch screen, will also support this control.
Future Considerations: Controls to rotate the molecule are being considered as well.