Chemical Formula Tutor   
by Chemware Ltd   

Chemical Formula Tutor v1.3
Makes learning formula writing easy, at home or in class.
Chemistry Teachers and Students will appreciate the intuitive,
interactive Drag-and-Drop interface.
Helpful tips and cursors, built-in Atom Counter, Learn Mode,
Test Mode (with or without timing), and scoring.
Customise Levels and Formulas (among other things)
with the intelligent Editor.