Key Ideas from the Lessons:
- Develop and use models to explain the how the structure of molecules (specifically how the molecular structure moves) determines if they function as gases, liquids, and solids.
- All atoms and molecules are in constant motion
- There are differences in the spacing, motion, and interaction of atoms and molecules that make up solids, liquids, and gases. The particles of a gas (atoms or molecules) are much farther apart than the atoms or molecules of a liquid or a solid. Because atoms or molecules of a gas are so far apart they rarely come in contact with each other. In solids and liquids, the atoms or molecules are packed closely together.
- Although the motion of atoms or molecules of a solid is severely restricted, the atoms or molecules are constantly moving back and forth in all directions with respect to a fixed position. In liquids, the motion of the atoms or molecules is limited but the atoms or molecules can still move rapidly back and forth with respect to a fixed point, around a fixed point, and past each other from one fixed point to another. Atoms or molecules of a gas move freely and spread out throughout the container they occupy.
- Similar to the pushes and pulls between magnets, atoms or molecules also push and pull on each other. In solids, the atoms or molecules pull strongly on each other and are linked together in rigid structures. In liquids, the atoms or molecules pull less strongly on each other, are more loosely connected, and form less rigid structures. In gases, the pull between atoms or molecules is so weak that they do not form structures.
- Hardness, flow, and compressibility are macroscopic properties for which students are expected to know the molecular reasons Solids are hard because the atoms or molecules are linked together tightly in rigid structures, not because the individual atoms or molecules are hard. The atoms or molecules of liquids can easily move past each other from one fixed point to another but do not move apart from one another and that this is why liquids flow and take the shape of their container but solids do not. Gases can be compressed because the atoms or molecules are not as close together as they could be, not because the individual atoms or molecules are soft.
This lesson just explains how molecules behave in solids, liquids, and gases. The next lessons focus on energy and then we will link how thermal energy causes these states of matter to change.
Summary of the lesson:
Lesson 1: Ask students in groups of 3 to come up for a rule about what makes matter solid, liquid, or gas. Accept all answers at this time. If no one brings up molecular movement, do so now. Show the tutorial and the summary and animated visual of how molecules move in solids, liquids, and gases. Ask students in to become human models of solid water molecules, liquid water molecules, and gas water molecules. Ask them to explain how their actions model the the three states. Move the desks to the walls so you have a clear place work. I pass out one O- letter to every 3rd student and H+ letters to the rest. They just tape it on their front shirt. The main thing to watch for is that the 3 students should stick together as H2O best modeled by linking arms with O in the middle. They become liquid molecules when the H20 groups slide past each other. Solid H2O groups just vibrated back and forth next to each other. Gas H2O groups bounce around the room (a favorite state of matter for 6th graders). Having them start as individual atoms reinforces key ideas from the previous lessons. It is challenging to get the whole class to work together to form H2O groups(molecules) and then decide how to behave to model ice, water, and water vapor. There is definitely “engaging in argument from evidence” happening with this activity but don’t tell students what to do. If they ask, just point them to the tutorial resource or the other resource. If they do not form into H2O groups, ask them what they are representing. If they say water, ask them what atoms make up water and if that’s what they are modelling. It does end up clicking and is a fun activity. An extension to this activity is to tell students that weh H20 molecules bond as a solids the opposite charges attract. So the H+ of one molecule need to be vibrating next to a O- of another molecule. Ask students to describe what kind of shape this makes. Then, ask them if this makes them more dense or less dense than liquids. How does this explain why ice floats in water? Tell students that most molecules become more dense when a solid but that water is a unique molecule. Afterwards, in small groups of 3-4 students, answer the probing questions:Matter Final Formative Assessment. Answers must be supported by evidence. They can use any resource available in the classroom for assistance. These probing questions addresses misconceptions students may hold about the key ideas of the lessons. Discuss how what we learned about matter fits into the cross cutting concepts. Discuss what science and engineering skills they practiced while learning the concept.
If students begin asking what makes molecules move differently, refer them to the anticipation guide from the first lesson matter and energy unit Anticipation Guide and ask them to read over #8 and make a prediction.