The objective of this project is to create a new module on the nature of chemical bonding, revising one of the most fundamental components of undergraduate general chemistry. In place of memorizing rules, the new strategy develops an understanding of the nature of bonding by exploring the process by which atoms combine to form molecules, with an emphasis on developing predictive intuition. Context is supplied by focusing on molecules in real world situations, such as the gases that constitute Earth's atmosphere. The web-based, extensively visual module is being developed by expert working scientists with the aid and advice of seasoned general chemistry lecturers. It is being tested in the classrooms of the University of Illinois and modified in response to assessment of student comprehension. The performance of chemistry major volunteers is being tracked through subsequent courses. In addition to critical input from general chemistry lecturers, critiques from instructors of later courses that depend upon a solid legacy understanding of bonding developed in general chemistry also are used to improve the module. Instructors are being trained in the new material through local workshops and resources on the website, including video. The website establishes an online community to serve as a nexus for implementing the module beyond the University of Illinois. Intellectual Merit. A great need exists to transform the manner in which chemical bonding is taught in general chemistry, to update the material to reflect the current state of knowledge, and to address and avoid common misconceptions. The new module is founded on rigorous quantum chemistry and is richly supported with both static and animated graphics. Each lesson is approached heuristically, through discovery of principles rather than as rules to be memorized, thus employing the same reasoning process working scientists use to study basic phenomena. By pursuing this strategy in the new module, the students develop their ability to confront the mysteries of the subject and construct an effective cognitive framework for understanding bonding. The approach builds a coherent narrative that connects atoms and their properties to molecules and their properties. It emphasizes connecting theory and its symbolic representations to actual molecules in real world contexts. Broader Impacts. This project is having a broad impact on STEM education in several respects. (1) Impact from improving the chemistry curriculum. The project's subject matter lies at the core of chemistry and thus impacts all of the diverse sub-disciplines and applied fields of chemistry that depend upon a sound understanding of the nature of bonding. The new module is expected to provide a better foundation for developing deeper and more sophisticated understanding of the subject in subsequent courses. (2) Impact from improving introductory chemistry. The new classroom materials should improve the fundamental knowledge of all students who take introductory chemistry and provide them with better lifelong understanding of the subject. Improvement of introductory courses also helps to increase student interest in STEM careers. (3) Impact through developing a model for course revision. As an archetype for revising a subject where much of what is taught is a matter of tradition that has not kept up with advances in the state of knowledge, this project provides a template for revising the entire general chemistry course as well as courses in STEM disciplines beyond chemistry.