The app I found is called "molecule" and it is a really cool app for chemistry and science. It is a free app found here:
itunes.apple.com/us/app/molecules/id284943090?mt=8
From what I could see there were a lot of pros. You can look up any molecule and it would bring up a list to choose from. From that you can move around the composition of whatever you choose to get a visual of what it looks like. It would be really applicable to use in a chemistry classroom. It also shows the number of atoms when you click to extend the description of whatever molecule you chose. I would definitely have my students in a chemistry class use this app so they can have a more in-depth look rather than a picture or a slide to look at. The cons? I couldn't really see any because it is a free version so I do not expect a lot from free apps.