The purpose of this assessment probe is to elicit students’ ideas about atoms and molecules. It is designed to reveal commonly held ideas students have about the structure and properties and provides students an opportunity to use the scientific practice of developing and using conceptual models. A suggestion is to provide students with an opportunity to revisit this probe after they have gained more knowledge about atoms and molecules and have further developed their particle model. The probe is provided in English and Spanish. A materials list, teacher notes, standards, assessment, and references are provided. This book selection also includes the Table of Contents, Preface, Acknowledgments, Dedication, About the Authors, Introduction, and Index.