In this interactive activity, students view six models to investigate what a gas, liquid, and solid look like at the atomic level. Choose to view a gas or liquid made of atoms only, a gas made of diatomic molecules, a liquid made of triatomic molecules, or two types of solids. In each simulation, users may highlight an atom and view its trajectory to see how the motion differs in each of the three primary phases. Don’t miss the extension activity: a side-by-side comparison of the atomic structure of a hot liquid and a cold liquid. If you click “”Withdraw the Barrier””, the two liquids mix. Which state of matter has stronger attractions between atoms? Editor’s Note: Teachers who complete the free registration may take snapshots to capture data and store student work. This item is part of the Concord Consortium, a nonprofit research and development organization dedicated to transforming education through technology. The Concord Consortium develops deeply digital learning innovations for science, mathematics, and engineering.