Unit 3.1 How can we observe the unobservable?

By the end of this unit, students will be able to:

• Demonstrate that matter is neutral and collect data in order to demonstrate that matter can become positively or negatively charged
• Explain how it can be known that atoms are composed of protons, neutrons, and electrons in order to explain the structure of an atom
• Explain how theoretical models can be developed for phenomena too small to observe directly

This unit is designed to provide an interactive and introductory way for students to practice making observations about matter too small to directly observe (the atom) and use their own experiments and data to interpret that matter can be neutral or become charged. Students will use their findings to test historic models of the atom in order to understand and explain why those models worked and were revised. This entire unit can be used as an extension unit for classes with labs and/or more emphasis on chemistry. The tape activity follows the balloon demonstration and is designed to provide an interactive and introductory way for students to practice making observations, documenting data, and comparing datasets.

These materials build a foundation for understanding the unit's motivating question, but also function well as a standalone module. The materials in this unit should take 2.5 hours of class time (1.5 hours if either of the tape or atom model activity is skipped). Most of the lab exercises rely on small group work and are best suited to smaller classes or a lab.

Teaching Materials:

All Slides: U3.1 All Slides.pptx (PowerPoint 2007 (.pptx) 3.1MB Jul9 24)

Atom Table Key:

atom table key.xlsx -- educator-only file

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Materials:

• Tape Experiment: Clear tape, markers for each group of 2
• Atom model activity: balloons, something to make the balloons staticky (fleece/wool/hair...), something to stick to the staticky balloons (packing peanuts? Wall? Head of hair?)
• Other Materials: computer and projector, white board or chalk board with markers/chalk.

Reflection: U3.1 Reflection.docx (Microsoft Word 2007 (.docx) 263kB Jul9 24)

Sample Student Reflections (this is Reflection 7): Reflection Examples Redacted.pdf (Acrobat (PDF) 1.8MB Jul8 24)

The Lab(s) is/are assessed as a Science Journal, as always. Science/Lab Journals General Instructions/Rubric (Microsoft Word 2007 (.docx) 2.9MB Aug30 24)

Pre-Class Assignment(s):

Pre-class reading Modeling in Scientific Research. Students answer these questions related to the reading:

• Why is modeling useful in science?
• What types of models were you familiar with prior to this reading?
• Which are new?
• Which are you most curious about?

In Class: (135 min)

Introduction (10 min):

Using balloons to demonstrate some fundamental properties of matter

• We cannot see atoms easily so we will use balloons to demonstrate some fundamental properties of matter and use our observations to make interpretations about atoms. First students will inflate their balloons and try to stick them to things (e.g. wall, friend, etc.) without rubbing it on anything. Balloons should not stick to anything. Then students will rub their balloons on fleece/hair/wool to make them staticky and then try to stick them to things. Balloon should now stick.
• What does this demonstrate? In the first part, where the balloon doesn't stick to anything, this represents that matter is neutral. In the second part, the staticky balloon represents that matter can be charged and hold a charge for some amount of time.

Think-pair-share (5 min):

Students discuss the following questions:

• Can we SEE the charge?
• Did the uncharged balloon look different from the charged balloon?

Extension Tape Experiment (60 min):

• In this experiment students will work in pairs of groups of three using strips of clear tape. They will set up the experiment to record data of whether the strips of tape attract or repel each other. Data recording first happens in the pairs/groups with the students documenting their observations as they run trials.
• After initial data collection, groups share their data with the class to compile a class data set. Students will make simple bar graphs comparing their data with the whole class dataset to look for trends and make interpretations from their observations.
• The activity wraps up with a full class discussion about making and interpreting direct and indirect observations from the context of the tape and balloon experiments.

Extension Examining the Evolution of the Atomic Model (60 min):

• This is a conceptual scientific examination of atomic models to determine if and how the models support the following two "balloon-and-tape" based premises:
  • Given that matter is neutral, can this atomic model predict that matter is neutral?
  • Given that matter can be positively or negatively charged, does this atomic model allow for matter to be positively or negatively charged?
• For each premise, if the atomic model does work, then it must be explained how.
• You will guide students through this conceptual scientific evaluation of the first atomic model to demonstrate how to consider the premises listed above. Then the students will work through, in pairs or small groups, 8 more atomic models.
• When students have completed their analysis, you will lead a discussion to go through all the models and the correct answers. Some of the models are the historic Thompson, Rutherford, and Bohr models. These are to be discussed in more detail. Lastly, the Quantum model is introduced.
• This activity ends with three discussion questions for the students to consider:
  • How is the atom system organized?
  • How do we know?
  • What do we not know?

Ask students HOW they know what they know about atoms. Expect them to "know" basic atom facts based on "learning in school". Or perhaps they don't really "know" (or remember) and that's totally ok! That's the point! Part of the goal of this activity, observing the unobservable, is to replace "face-value trust" in science (or ummm random social media memes propagating fake science) with a window into how it is possible to demonstrate observing and interpreting physical phenomena without being able to directly see what is happening. This exercise will not result in concrete proof of electrons in everyone's pockets, but everyone should, ideally, have an idea of how the model of the atom we accept today came to be accepted through the process of scientific inquiry.

For the tape activity, begin by organizing students in small groups, ideally fours with two sets of pairs. If there are odd numbers, groups of 5 are fine. Each group should set up a data collection table with three columns titled: T/T, B/B, and T/B. They should allow several rows to log data from multiple trials. Designate the letter "a" as short for "attract", the letter "r" as short for "repel", and "0" for nothing. Tops will repel tops, bottoms will repel bottoms, and tops and bottoms will be attracted to each other. Students should record their data from each trial as one of these three symbols for consistency of data collection within the whole class.

A pre-class assignment (described above) is graded for completion only, not correctness. Administer using the same format throughout your course (through the LMS, turn in paper copies, guided discussion/participation in class, etc.). Consider setting the due date an hour or so before your class begins to give you time to summarize where your students sit with these concepts (this is a form of Just in Time Teaching).

The Labs and activities are assessed as a Science Journal, as always. Science/Lab Journals General Instructions/Rubric (Microsoft Word 2007 (.docx) 2.9MB Aug30 24)

The reflection assignment in this unit asks students to read the article Atomic Theory (visionlearning) and reflect on this reading within the context of their experience using the experiments and conceptual models of the atom from this unit. What similarities are there between the historical process of scientists coming to understand the atom and our own process? Provide specific examples. As always, reflections ask students to put their learning in their own words and also to apply their knowledge in a new and novel situation. Reflections should be about 500 words and they should both discuss content that reflects understanding and thoughtfully reflect on the materials.

Tape activity is adapted from NSTA's tape activity.

Readings:

• Vision Learning Modeling in Scientific Research
• Vision Learning Atomic Theory

PhET simulations:

• Balloons and static electricity
• Rutherford atomic model and Plum Pudding atomic model