NGSS and the new AP chemistry curriculum have included modelling in the chemistry curriculum, so it is imperative that we have access to good conceptual questions surrounding modelling. I am in the midst of researching the best sources of these types of questions and resources that will help teachers to design their own. If you have any suggestions, please post them here.
I used JCE Classroom Activity #111 in my chemistry classes today. (Subscription to JCE required.) What a great way to help students make the connection between number of ions present, the charges of the ions and the neutral compound formula.