Distinguish between a model and the actual object, process, and/or events the model represents. Compare models to identify common features and differences. Develop and/or use a model to represent amounts, relationships, relative scales (bigger, smaller), and/or patterns in the natural and designed world(s). Develop a simple model on evidence to represent a proposed object or tool. frequent and regular occurring events. Develop a model using an analogy, example, or abstract representation to describe a scientific principle or design solution. Develop and/or use models to describe and/or predict phenomena. Develop a diagram or simple physical prototype to convey a proposed object, tool, or process. Use a model to test cause and effect relationships or interactions concerning the functioning of a natural or designed system Use and/or develop a model of simple systems with uncertain and less predictable factors. Develop and/or revise a model to show the relationships among variables, including those that are not observable but predict observable phenomena. Develop and/or use a model to predict and/or describe phenomena. Develop a model to describe unobservable mechanisms. Develop and/or use a model to generate data to test ideas about phenomena in natural or designed systems, including those representing inputs and outputs, and those at unobservable scales. (c) Crosscutting Concepts: Scale, Proportion, and Quantity The concept of scale builds from the early grades as an essential element of understanding phenomena. Young children can begin understanding scale with objects, space, and time related to their world and with explicit scale models and maps. They may discuss relative scales—the biggest and smallest, hottest and coolest, fastest and slowest—without reference to particular units of measurement. Typically, units of measurement are first introduced in the context of length, in which students can recognize the need for a common unit of measure—even develop their own before being introduced to standard units—through appropriately constructed experiences. Once students become familiar with measurements of length, they can expand their understanding of scale and of the need for units that express quantities of weight, time, temperature, and other variables. (NRC 2012, pages 90–91) Crosscutting Concepts in the NGSS cites the following (): In grades K-2, students use relative scales (e.g., bigger and smaller; hotter and colder; faster and slower) to describe objects. They use standard units to measure
Leave the beaker of salt on a window sill in in some place where maximum evaporation will occur for approximately 3 days. After 3 days, observe the contents of the beaker. You may use a microscope or a hand lens to get a better view of the substance in the beaker. Record your observations in Table 1 of Student Lab Sheet. Use the molecular model kits to build both the salt and the water molecules Sketch the salt and water molecules in the final column of the Student Lab Sheet. Your teacher will lead a class discussion of the question found in the Student Lab Sheet. How did you make models that describe the composition of salt and water molecules? Write your answer to the question on the sheet based on the class discussion. water molecules. Additional emphasis should be placed on how this process forms a homogeneous mixture that is impure substance. Explain to students that you will continue with the experiment in three to four days depending on when the water has evaporated. (This next portion will engage students in the Practice of Analyzing and Interpreting Data1) After 3 or 4 days allow students to look at the contents of the beaker. They may use a microscope or hands lens to examine the crystals that have formed, or they may simply use the naked eye. This next portion will engage students in the Practice of Developing and Using Models4) Instruct students to use the molecular model kits to build salt and water molecules. They should then sketch the molecules in the final column of Table 1 in their Student Lab Sheet. Emphasize that these sketches are types of models that help us to visualize the differences between molecules (which are extremely small)of the two different pure substances. Engage students in a discussion about how molecular models were developed to describe the composition of the salt and water molecules. This will help them answer to the question on page 1 of the Student Lab Sheet: How did you make models that describe the composition of salt and water molecules? Explain to students in Part 2 they will construct models of other pure substances to determine if they are similar to sodium chloride. They will also use a model to show how evaporation leads to the formation and growth of sodium chloride crystals.
Methane (CH4) Hydrogen (H2) Once you have completed your models, determine which molecule has a structure most similar to the sodium chloride. Mix the nuts and bolts in a small bowl. The nuts represent chlorine atoms, the bolts represent sodium atoms and the buttons represent water molecules. Discuss with your group how this model could be used to show the crystallization of salt form during evaporation. Use modeling clay and sticks to create a model of a large salt crystal formed by evaporating salt water. Sketch your model in the student lab sheets on page XX Assist students who are having trouble building the molecules from the chemical formulas. Students should identify potassium chloride as having a similar structure (linear composed of two different atoms) Facilitate group or class discussions which lead to an understanding of how the model for crystallization works. Students should understand that as water molecules (blue buttons) evaporated (removed) the chlorine atoms (nuts) and sodium atoms (bolts) move closer together. As they move closer together, they join to form crystals. As more water molecules are removed, more sodium and chlorine atoms join causing the crystals to grow. NOTE: Remind students that the shape of the sodium chloride crystal remains cubic no matter how big or small the crystal is. This is due to the atomic structure of the sodium chloride molecule. (This next portion will engage students in the Practice of Constructing explanations and designing solutions2) Ask students: Do you think it is possible to use this crystallization model for other compounds? Guide the student discussion to recognize that the model for potassium chloride has a similar number of atoms and has the similar linear shape, therefore it may have similar characteristics or properties as sodium chloride. As a result, students should recognize that this same process might be used in models that are similar in composition to sodium chloride such as potassium chloride.
Referred Practices 1. Analyzing and interpreting data in 6–8 builds on K–5 experiences and progresses to extending quantitative analysis to investigations, distinguishing between correlation and causation, and basic statistical techniques of data and error analysis. Analyze and interpret data to provide evidence for phenomena. Analyze and interpret data to determine similarities and differences in findings. 2. Constructing explanations and designing solutions in 6–8 builds on K–5 experiences and progresses to include constructing explanations and designing solutions supported by multiple sources of evidence consistent with scientific ideas, principles, and theories. Construct an explanation using models or representations. Apply scientific ideas, principles, and/or evidence to construct, revise and/or use an explanation for real-world phenomena, examples, or events.