The growing popularity of flipped, blended, and online learning, combined with the need to support a student population with increasingly diverse backgrounds, has led to the development and use of online materials to support students' learning of chemistry outside of a face-to-face classroom. Chemistry simulations provide opportunities to make such materials more interactive; however, it is important to understand how to best employ them to support students' independent learning outside of the classroom. The larger ChemSims project aims to determine how screencasts and simulations can be used to best support the development of students' conceptual understanding of core chemistry concepts in such environments. This paper focuses specifically on the concepts of force and energy as they pertain to bonding and intermolecular attractions. It describes the investigation of students' out-of-class use of a PhET simulation that illustrates force and energy changes that occur when two atoms come together or are separated. As an introduction to bonding, students completed out-of-class assignment questions in one of three different treatment conditions: (1) exploring the simulation directly using guided instructions; (2) watching an expert-narrated screencast using the same simulation; or (3) watching an "enhanced screencast", consisting of the expert-narrated screencast plus additional information related to the formation and breaking of bonds in chemical reactions. Comparing scores on pretest and follow-up questions indicated that all treatments resulted in small learning gains with some learning objectives indicating greater gains than others. Further, findings indicate that the enhanced screencast was able to help students better connect this concept to the phenomena of ATP hydrolysis. Finally, using eye tracking to contrast student use of the simulation as compared to the screencast in completing the assignment suggests that, while the screencast may not result in increased conceptual gains, it may serve to make the assignment seem easier than if students are required to engage with the simulation themselves to work through the initial questions.