As a review, ask students to sketch the molecular structure of solids, liquids, and gases (draw boxes and use circles to represent molecules). As a self-check/review, play the video Solids, Liquids, Gases (3:25) (http://studyjams.scholastic.com/studyjams/jams/science/matter/solids-liq...) by StudyJams! After viewing the video, give students an opportunity revise or redo their sketches. (*Note: There actually are four states of matter (solid, liquid, gas, plasma), but only solids, liquids, and gases occur naturally on Earth.)
2 Direct Instruction
First, play Flocabulary’s song, States of Matter (4:14). Next, describe how states of matter can undergo a phase change, meaning a change in structure and properties. Use H2O, water, as a concrete example. If possible, show how ice, a solid, has a definite volume and definite shape (demonstrate how it doesn’t change with the container it’s in), liquid H2O has a definite volume but not a definite shape (measure amount but then pour into different size containers), and H2O in its gas state has no definite volume and no definite shape (the water vapor is all around us, but is invisible!)
Next, describe how these states can change. Diagram the molecular structure of H2O, and describe how it will undergo a physical change due to temperature. Start with its solid state, ice. With increased temperature, the molecules begin to move with more energy and melt or turn into a liquid at O°C (32°F), known as its melting point. Keep increasing the temperature, and liquid H2O begins to move even more rapidly, and at its boiling point, 100°C (212°F), will vaporize into gas, water vapor (solid à gas is sublimation). Conversely, removing heat will cause water vapor to condense and turn back into liquid H2O below 100°C (212°F). As temperature decreases, the molecules in liquid H2O slow down, and at its freezing point, O°C (32°F), freeze into a solid. If time permits, provide students with the lyrics of the song, States of Matter, and, as a group, search for and identify the key vocabulary terms you have talked about today.
(*Note: Most solids have a greater volume than its liquid state, with the notable exception of H2O. Water’s solid state has a greater volume than its liquid – therefore causing pipes to crack when water freezes.)
3 Guided Practice
In small groups, have students work together to explore the Phase Changes Gizmo http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=557) in Explorelearning. Have groups follow the prompts and play with the interactive in order to answer the questions in the Student Exploration Sheet.
4 Independent Practice
Challenge students to take photographs of the three states of H2O in the real world. They will have to use “artistic license” when representing water vapor (invisible!) Have them use ExplainEverything to 1. demonstrate their understanding of the properties of the three states of H2O and 2. explain how phase changes occur for H2O. Encourage students to use images, text, and even video in their presentations.
Ask students to research Charles’s Law, also known as the law of volumes. The law states that the volume of gases expands with increased temperature. To illustrate this physical change, have students microwave a bar of IvoryTM soap for 90-120 second at home (give careful instructions for using the microwave). Ask them to record their observations (written notes, photographs, video), and then in class discuss their theories about what happened. Explain that the energy of the microwave causes the gases of water and air inside the soap to expand; due to the soft nature of the soap, the expanding gas get trapped inside the soap (causing it to become a foam). (*Note: must be IvoryTM soap as others don’t contain as much whipped air; which you can see evidence of if you cut into a bar of IvoryTM soap.