Structures of a Molecule - Grade 7
Overview
Middle school lessons utilize local phenomenon and are organized by grade bands. By designing instruction around local phenomenon, students are provided with a reason to learn shifting the focus from learning about a disconnected topic to figuring out why or how something happens. #Going 3D with GRC
Lesson - Composition of Simple Molecules
Student Science Performance
Phenomenon: Water smells good, but when I add ammonia to water it smells bad.
Gather:
Students develop questions to investigate the structure of various substances to find clues for how differences in molecular structure may cause differences in observable properties.
Students investigate putting household substances into the water to determine differences in the way these substances interact with water.
(Teaching Suggestions: The lesson focuses on the idea that the structure of a substance determines the properties of the substance. This idea is used to have students build gumdrop or tinker toy structures of simple substances to show differences and then they discuss that the structure of molecules affects the properties of substances. The focus is on students building models to initiate a discussion that substances have different structures that can be represented in models. Students will not know why structures are different or how differences in structures affect properties.)
Materials: ammonia, salt, sugar, water, baking soda, vinegar, corn starch, sand, etc.) An investigation could be to see how the volume of water changes when different substances are placed in the water. A glass brim-full of water will overflow when a tablespoon of sugar is added, but not overflow when a tablespoon of salt is added (a sugar molecule is large enough to displace the water molecules, salt ions [sodium and chlorine] are not). This will likely be an investigation you will need to direct students to do if you want to add this to the list of properties The sugar molecule is so large that you may wish to have a single class model for sugar. Students will need to create a data table to record observations of household substances and water-see Appendix B-4. Safety note: students should wear safety goggles during the investigation.
Reason:
3.Students analyze molecular models of substances to find the patterns that substances with different structures interact with water and/or with our noses and can be detected in qualitative ways.
4. Students construct explanations that the structure of substances cause them to have different properties.
(Teaching Suggestions: # 5 is looking at the investigation of putting different substances into water and having different smells (e.g., ammonia, alcohol) or different rates of dissolving or volumes in water (e.g., sugar, salt) a data table with the molecular structure and boiling point to find the pattern that the larger the molecule, the higher the boiling point. Students are basically going to say that these things that have different properties have different structures. Hopefully, students will identify a pattern in the data table, but they may not see a pattern.)
Class Discussion:
Q: How does the structure of a substance affect the properties of that substance?
Q: How can substances like carbon dioxide and carbon monoxide that have the same atoms in each
have very different properties?
Q: How does the arrangement of atoms in a substance affect its properties?
Q: What caused the ammonia substance to smell bad?
Q: Why do salt and sugar behave differently when dissolved into the water?
(Teaaching Suggestions: Carbon dioxide is not harmful and we breathe it out all the time, but carbon monoxide is a poisonous gas. The structure of ammonia interacts with the smell receptors in our nose and cause us to interpret a bad smell. Each substance has a different structure so it interacts with our smell receptors in different ways.)
Communicate Reasoning
5. Students develop a model to represent the simple molecules of carbon dioxide and water.
6. Students use a model to describe the structure of salt with an extended crystal structure and how it is different than the molecular structure of sugar.
7. Students develop models to support the explanation that substances made from the same type of atoms, can combine to make different structures that have different properties.
(Teaching Suggestions: # 7, 8, and 9 are a progression. Evidence comes from the reading.)
*See attached document below for full lesson.
Additional Lessons can be found at #Going 3D with GRC (Gathering, Reasoning and Communicating). Original authors were: Kristen Gagesch, and Kenneth Huff.