University of Virginia
Physics Department

## Not So "Bohr"-ing Atoms

A Physical Science Activity

Adapted from: Keiffer, B. (1995). Atom Illumination. Science Teacher, 62:1, pp. 29-31.

2003 Virginia SOLs

• PS.1
• PS.3
• PS.4

Objectives

Students will

• construct Bohr models of atoms;
• interpret data from the periodic table;
• use atomic number and atomic mass to determine structure of atoms.

Motivation for Learning

Driving Question

How can we make a model of an atom? Atoms are much too small to be seen, but experiments on the behavior of atoms have allowed us to understand that an atom is made up of protons and neutrons in the nucleus and electrons in various orbitals around the nucleus. Because the atom is so small and the electrons move so quickly, it is difficult to know exactly how an atom looks. However, we can develop models to help us understand them better.

Background Information

This activity is written using the old toys called "Light Brites" that consist of plastic pegboards in front of a light bulb. Colored plastic bulbs are inserted into the peg holes to make a lighted picture of sorts. Those actual "Light Brites" may not be available in all classrooms; some schools have made a commitment to teach science with toys when possible and may have several of the toys available. Other objects could be substituted for the light bright such as "Chinese Checker" marbles and boards or even pieces of paper to represent the atomic components. The main idea is to provide students an opportunity to produce a two dimensional model of the Bohr atom in the class where teacher feedback is readily available.

The model fails to illustrate the modern atomic model that places electrons in specific orbitals in a three-dimensional space-filling model. However, it illustrates that electrons occupy areas of varying distance from the central nucleus.

### Student Activity

Materials

• Light Brites (one per group of 4 students)
• Bulbs for Light Brites (100 bulbs per group preferably of only 3 colors if possible)
• Student activity sheets
• Periodic Tables
• Balance

Procedure

1. Tell the students they will work in groups to make models of four common elements. Explain that the model has several shortcomings (outlined in the "Background" section for this lab).
2. Divide students into groups of four. Throughout the exercise, each student will be assigned a specific job. The students will rotate through each of the four jobs for each atom to offer everyone an opportunity to perform all responsibilities. The jobs include:
• Researcher-locates the assigned atom on the periodic table and ascertains the atomic number, atomic mass.
• Calculator-Calculates the number of protons, neutrons, and electrons in the atom.
• Designer-Decides on the position and arrangement of the parts of the atom to be constructed.
• Builder-Places the bulbs in the designated positions on the Light Brite.
3. Assign the class four different atoms to construct (hydrogen, oxygen, carbon, and sodium, for example).
4. One student from each group retrieves the Light Brite and 100 bulbs, in a sealed sandwich bag, from the teacher. (Massing the bulbs before the activity and after will help ensure all are returned.)
5. Each group constructs the first atom assigned by the teacher on the Light Brite. The bulbs for the protons and neutrons should be grouped as a nucleus at the center of the Light Brite board. The bulbs representing electrons should be distributed around the nucleus according to the accepted valence arrangement. When a group completes construction of an atom, it should request that the teacher inspect the work. Once the teacher approves the model, each student should sketch the arrangement on the "Data Sheet".
6. For each of the subsequent atoms, the students within the group will rotate so everyone fulfills each responsibility.

 Figure 1: A two-dimensional model of a sulfur atom using 1 inch paper circles to represent protons (blue), neutrons (green), and electrons (red).

 Figure 2: Atomic model of a magnesium atom using gumdrops to represent protons (green), neutrons (red), and electrons (orange).

Data Sheet

 Atom #1 _______________ Atom #2 _______________ Atom #3 _______________ Atom #4 _______________

Extensions

1. Students pick an element to research using web and library sources.
2. Students produce a power point presentation on their element.
3. Students post their element presentation to a class web page as part of a "Cyber Periodic Table."

Students with Special Needs

This activity is accessible to most students; though if a student is unable to manipulate small objects comfortably, the students within the groups may not be able to rotate through all jobs assigned.

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

Assessment

1. Students draw arrangements of other atoms independently.
2. Students independently make a two dimensional model of an atom to be assessed by the teacher for accuracy.