In this activity, learners build models of atoms and molecules, then consider their role in different phases of matter, density, and mixtures and solutions. The atomic models are made first from play dough, then from molecular model pieces. The phases of water are considered from a molecular point of view using a drawing. Oil and water are used to convey the relationship between mass and volume (density). Salt and pepper are used to show that some solids dissolve, and others don't. The activity is written to be part of a kit that can be checked out of the library, but the kit is not required.