The Butterfly Orbital

Introduction

A centrifuge can be used to provide a physical model of electron orbitals. Students often initially experience difficulty in visualizing abstract concepts like the quantum mechanics of the atom. This demonstration provides students with a simple, visual analogy of electron motion around the nucleus.

Concepts

• Uncertainty principle
• Orbitals
• Probability
• Electron density

Materials

Safety Precautions

This demonstration is considered nonhazardous. Follow all normal classroom safety precautions, wear safety glasses. Do not touch the motor axle while the rotor is spinning. Remove the battery from the Bracken’s Demonstration Spinner when not in use and during storage.

Procedure

1. Heat a dissection needle or paper clip with a candle or burner. Melt an off-centered hole in the top (flat surface) of the soda bottle cap. The hole should not be in the center of the cap (see Figure 1). Melt a second hole into the side of the cap. This hole helps to secure the butterfly’s wire.
   {11983_Procedure_Figure_1_Holes in the top and sides of cap}
2. Cut the florist’s wire in half (9") using scissors. Attach the 9" wire to the wire that extends from the butterfly. Do this by twisting the two wires together (see Figure 2).
   {11983_Procedure_Figure_2}
3. Flip the cap upside down so that the flat surface of the cap is down (toward the countertop).
4. Thread the other end of the florist’s wire through the hole on the side of the cap and twist as shown in Figure 3. Tighten the loops as much as possible to steady the wire.
   {11983_Procedure_Figure_3}
5. Bend the wire into a question mark shape so that the butterfly is just off-center from the spinning axis (see Figure 4).
   {11983_Procedure_Figure_4_Cap flipped upside down and connected to Bracken’s Demonstration Spinner}
6. Flip the cap upside down and connect the cap to the motor axle of the Bracken’s Demonstration Spinner.
7. Connect the battery to the motor. Turn on the motor and the butterfly will spin in a fairly chaotic manner. The wire may need to be adjusted to achieve the desired effect.

Student Worksheet PDF

11983_Student.pdf

Teacher Tips

• Bracken’s Demonstration Spinner, Flinn Catalog No. AP6202, is required and sold separately.
• Extra wire is included to replace the initial wire if it should become worn.
• This demonstration may be repeated as many times as desired with the same device.
• While numerous analogies have been used over the years, this demonstration can be performed quickly to make a lasting impression on students. By showing this visual example of a fast-moving butterfly, students may see the connection to abstract ideas such as probability and location of electrons.
• To create more random movement of the butterfly, the wire may be tapped.

Answers to Questions

1. Describe the movement of the butterfly.

   The butterfly spins around in random, chaotic circles.

2. What does this demonstration show about the movement of electrons?

   This demonstration shows how electrons do not have a specific orbit they follow around the atom’s nucleus. Rather, they circle the nucleus in a random way and could be any given position from the center at any point.

3. What is Heisenberg’s uncertainty principle?

   Heisenberg’s uncertainty principle states that the position and energy of electrons cannot be determined simultaneously.

4. Referring to the diagram above, where do you think you are more likely to find an electron, in the center or around the edge of the cloud?

   You are more likely to find an electron in the center of the electron cloud, closer to the nucleus, than around the edge of the cloud.

Discussion

All atoms are composed of a nucleus (containing protons and neutrons) and electrons spinning around the nucleus. A common misconception is that the electrons orbit the nucleus similar to the way that planets orbit the Sun—in neatly placed relatively circular orbits. The actual location of an electron around a nucleus cannot be determined. Objects at the subatomic level do not behave like objects in the macroscopic world. At the subatomic level, the position and the energy of subatomic particles cannot be determined simultaneously. This is known as Heisenberg’s uncertainty principle. If the position of an electron is determined accurately, then the energy of that electron will be very uncertain. Vice versa, if the energy of the electron is accurately measured, then it is nearly impossible to find the exact location of that electron. However, we can determine the probability of finding an electron of a certain energy in a given region of space.The probability distribution of locating an electron in a region of space around a nucleus is known as the electron density cloud. The electron density cloud represents the three-dimensional orbital of the electron around the nucleus. Figure 5 represents the s-orbital of an electron at a low-energy state. It shows that there is a higher probability of locating an electron at a short distance from the nucleus than further away from the nucleus.

References

Flinn Scientific would like to thank Jeff Bracken, chemistry teacher at Westerville North High School in Westerville, Ohio, for sharing his original idea with us.

Brown, T. L.; LeMay, H. E.; Bursten, B. E. Chemistry: The Central Science, 6th Ed.; Prentice Hall: Englewood Cliffs, NJ, 1994; p 189.

Hewitt, Paul G. Conceptual Physics, 3rd Ed.; Addison Wesley: Longman, California, 1999; p 605.

Wiger, G.; Dutton, M. L. J. Chem. Educ. 1981, 58, 801–802.