University of Virginia
Physics Department

## Cloud Model of the Atom II

A Physical Science Activity

Adapted from Hutchinson, J. (1995). Inflatable Atomic Model, Science Scope, 18: pp. 43-44.

2003 Virginia SOLs

• PS.1
• PS.3
• PS.4

Objectives

Students will

• build a three dimensional model of an atom based on the cloud or quantum model;
• determine the number of subatomic particles and their relative locations using data provided on the periodic table;
• describe the relative sizes and masses of the nucleus and electron cloud in an atom.

Background Information

The cloud or quantum model of the atom is abstract and difficult to visualize. This model offers a three-dimensional representation for the student to ground understanding. Though the model possesses shortcomings, it offers the student insight into the density of the nucleus compared to the overall density of the atom. It further demonstrates the spacing to the electrons at relatively large distances from the nucleus. If the relative masses and sizes of the nuclear particles to electrons are large, the model emphasizes the important and natural size differential. It fails to show the quantum of orbital nature of the electron arrangement, however. Also, the nucleus is on the edge of the electron cloud unlike the expected central location. These deficiencies, however, can serve to bolster student understanding of the overall structure.

The models can be built by the teacher for demonstration and discussion. Conversely, students, individually or in groups, can build a model that reemphasizes the interpretation of periodic table data. With the models in hand, students can answer questions about them and can discover qualities of atomic structure rather than only receiving lecture based information on the topic.

Students must be reminded that when they are inflating the balloons, they must not inhale while their mouths are still on the balloon.

### Student Activity

To print out the Student Copy only, click here.

Materials

• Large round balloon (12 inch inflated)
• Small round balloon (water balloon size)
• 4 mm round B.B.'s
• 2 mm round B.B.'s (or small, lightweight beads)

Procedure

1. If the students are building the models, have each student or group select an atom between 1 and 20 from the periodic table that they wish to build. Tell them to determine the number of protons, neutrons, and electrons in the atom.
2. The students should retrieve the appropriate number of 4-mm B.B.'s to represent the protons and neutrons in the nucleus. They should place these B.B.'s in the small round balloon.
3. The students should next place the appropriate number of small (2 mm) B.B.'s into the larger balloon.
4. Insert the small balloon into the large balloon and hold the ends together.
5. Carefully inflate the small balloon while it is in the larger balloon. It should only be slightly inflated such that its walls stand out and it retains a round shape. Tie off the small balloon.
6. Inflate the large balloon while forcing the small one farther in. Continue to blow up the large balloon until it is fully inflated and much larger. Tie it off.
7. Write the symbol of the element, its atomic number and atomic mass on the outside of the balloon.
8. The student questions can be answered individually to check understanding or they can be used as class discussion.

Data Sheet

To print out the Data Sheet only, click here.

 1. Which atom did you model? Write its name and symbol in the space below.     2. How many protons, neutrons, and electrons are in your model? Number of Protons: _____________________ Number of Neutrons: _____________________ Number of Electrons: _____________________   3. What object(s) represent the protons, neutrons, and electrons in your model? Protons: _______________________ Neutrons: _______________________ Electrons: ______________________   4. Which part of your model has the greatest mass? ____________________________ (This part of the model with the greatest mass represents the nucleus of the atom. In a real atom, it is the heaviest part and has the greatest density too.)   5. Where are the electrons in your model? __________________________________ (In a real atom, the electrons are arranged at different levels from the nucleus, but are far from the nucleus. Most of an atom is empty space! In the model, the "empty space" is not really empty but occupied by air.)

Extensions

1. Students build a model of a different atom using different materials that they select.
2. Students research chemical properties of the element they modeled.

Students with Special Needs

The activity requires fine motor coordination to build the models. If students are not easily able to complete the activity as written, the teacher can construct the models for student examination and discussion.

Click here for further information on laboratories with students with special needs.

Assessment

1. Student responses on the Data Sheet will gauge individual understanding.
2. Have students describe the construction of another atom using the same materials.