Foiled Again! Using Macroscale Measurements to Determine Microscale Quantities

This activity is designed for students to apply their dimensional analysis skills to determine information about the size of individual atoms. This activity is also designed for the students to use their previous knowledge of density and volume to determine the thickness of aluminum foil. Students will also refine their measurement and scientific writing skills.

Concepts:
Dimensional analysis can be used to solve problems that normally could not be measured.
Density is a physical property of a substance that does not change with sample size.

Vocabulary:
-Density
-Volume
-Dimensional analysis
-Atomic radius

This activity is designed for a tenth grade 1st year Chemistry course with an ideal class size of 24 at a private high school. This is a guided inquiry activity designed to be completed in one 45 minute class period. There is no specialized equipment needed. Students should have a good understanding of density and volume calculations in order to be successful in this activity. The students should also be familiar with the mole-atom conversions, using molar mass and Avogadro's number. This activity is designed to be used after going over mole conversions during a chemical quantities unit. This activity is easily adaptable to any classroom.

This activity starts with the teacher asking some open-ended questions like: How big is an atom? How can we measure the size of an atom? After allowing the students 1-2 minutes to reflect on these questions, the teacher will explain how modern scientists measure atomic size (X-ray crystallography or computation). However, early chemists did not have access to the technology, but were still able to come up with very accurate atomic measurements and there are very good and less expensive means to estimate atomic values. After this discussion the activity sheet (attached) will be handed out. The teacher will review what density is and how we can measure volume of certain objects. The activity has a list of goals that the student needs to finish before the class period is over as well as a list of materials needed to complete the task. The students must write out their procedure done in the activity either in their lab notebook or on the activity hand out. The students will calculate the density of an aluminum atom by measuring the mass of an aluminum sample with a balance and the volume by water displacement. Using the fact that the density of an element does not depend on the sample size, the students can find the volume of an aluminum foil sample. Using that fact that volume is equal to length x width x height, the students will calculate the thickness of aluminum foil. Using Avogadro's number and the molar mass of aluminum, the students can find how many atoms are in their aluminum foil sample. Using dimensional analysis, students can calculate the volume of a single aluminum atom as well as the radius of an aluminum atom. To close the lesson, the teacher will give the accepted values of the calculated quantities for the mini-lab and discuss how accurate the macroscale measurements are at approximating atomic sizes.

This activity is adapted from:
Branan, Major Dan. "Mini-Lab 1: Foiled Again!" United States Air Force Academy Department of Chemistry. July 2007. assignment handout, instructor notes, and sample data (Microsoft Word 76kB Sep11 08)

Students can have a hard time using the density measured with a cylinder for their aluminum foil calculations. Teachers should reinforce the idea that density is a physical property that does not depend on how much or the shape of the substance you have. Since this activity is done shortly after introducing moles, students may struggle to see the connection with the measurements taken in the activity to the quantities that need to be calculated. This activity is different than what I have done in the past because it gives the students a hands-on problem to see how powerful unit analysis can be when dealing with atomic sizes and quantities.

Students will hand in the data sheet provided with all of their measurements and calculations. The teacher will be able to see if the students are making the proper connections from measurements to desired quantities.

IIA4-using the periodic table, IIA6-atomic interactions, IIA7-state of matter determined by interactions