I think the idea of the Table is interesting, but I don't find a program that looks it up to be terribly interesting. That is, it's just as simple to just look at the DATA table in a text file.

Maybe make it more interesting by making it into a Quiz? It will prompt you for something and check your result. That would be good for studying, when learning the table in chemistry class.

It doesn't handle the atomic weights. E.g. 1.00797 for H.

It could take a molecule description, parse it, and return the weight. That could be an interesting calculator.

—John