Misconception:


"Atoms have electrons circling the nucleus like planets circling the sun"


Figure 1: Solar System (Misconception view) http://www.edplace.com/userfiles/image/solar%20system.jpg
Figure 1: Solar System (Misconception view) http://www.edplace.com/userfiles/image/solar%20system.jpg

HeliumIon.png
Figure 2: The Misconception http://www.sr.bham.ac.uk/xmm/images/fmc/electrons_orbitting_480_253.jpg



Source of the Misconception:

There are several sources for the misconception, primarily generated from images used to teach the history of the atom. These images continue to be used and can be found in textbooks, television, and the Internet – all used by teachers seeking to explain complex concepts. The root cause is the difficulty in using models to explain abstract concepts.

RutherfordBohr.png
Figure 3: Rutherford-Bohr Model http://a66c7b.medialib.glogster.com/media/08/0860a880e757f61626c17a8a76e52e4073893c1bc74f4c0250cd240dbf0d5801/modern-atomic-model.png

A. Teaching the History of the Atomic Model

In studying the history of the atom, the Rutherford model from 1911 is the first model to suggest that the electrons are in motion around a central nucleus. Reviewing two high school chemistry textbooks illustrates this approach to teaching the history of the atom. In Chemisty: Matter and change (Buthelezi et al., 2013) the development of the atomic model is broken up into two chapters. Student are left with the image of the Rutherford model with the “orbiting” electrons as they learn more about the properties of the subatomic particles. In the next chapter the history continues with the Bohr model (1913) and finally the quantum mechanical model developed from the work of Schrödinger in 1926 is introduced. The textbook Chemistry (Staley et al., 2012) has similar models shown for Rutherford and Bohr, but the section Development of Atomic Models shows all models on one page, so the quantum mechanical model with an electron cloud is shown on the same page as the “orbiting” electrons models. Having all historical models visible on one page does a better job of clarifying the changes in our understanding of the atom.




EnergyLevelsCircles.png
Figure 4: Electrons per Electron Energy Level. http://www.tulane.edu/~sanelson/images/electshells.gif

B. Teaching Electron Energy Levels & Configuration
The misconception can be reestablished in high school chemistry when teaching electron configuration and valance electrons. The Bohr model is an important model - it does an excellent job of teaching the relationship of electrons and the periodic table.
Students are taught the relationship between the electron energy levels and the atomic orbitals. But the model in Figure 4 is intended to show the number of electrons per shell, not the probability of their location or motion. The electrons are not orbiting the nucleus like planets around the sun.





C. Animation of Atoms
The increasing availability of animated models has improved in recent years, yet animation can still be misleading as seen in these two video clips:



Refining the Misconception:


ElectronCloud.png
Figure 5: Electron Cloud http://reich-chemistry.wikispaces.com/file/view/00080041.jpg/185352475/00080041.jpg

A. Using Images & Models.
An important teaching objective is describing the limitations of models and developing modeling skills in students (Harrison & Treagust, 1996). Models are an intrinsic part of education when teaching unobservable phenomena and it is important that students understand their use to avoid mistaking the model for reality. In addition, teachers need to be aware of the student’s prior knowledge to avoid the development of the misconception during the actual lesson. Students may reconcile their limited prior knowledge with the new material and develop a distorted new understanding of the concept.

B. Teaching the History of Atomic Model

It is important to teach all the models together and to show how they build on one another. Compare and contrast activities can help identify the similarities and differences of the multiple models. Timelines, storybooks, and matrix are all good student activities for comparing the atomic models. The limitations of the Bohr model can be put in the proper context which allows students to move past their prior misconceptions. Some educators have gone so far as to state that the Bohr model should not be taught to avoid misconceptions (McKagen et al., 2008). The Bohr model is an important model and its importance in teaching chemistry outweigh its limitations. With proper education the misconceptions can be refined.


Interactive simulations are available to compare the different models:
http://phet.colorado.edu/en/simulation/hydrogen-atom
http://phet.colorado.edu/en/simulation/rutherford-scattering

C. Teaching Electron Energy Levels & Configuration

Most high school and college textbooks have images of the individual electron orbitals as seen in Figure 6. In order to visually incorporate the orbitals into an atomic model, the next step needs to be made as seen in Figure 7. Having the multiple orbitals arranged around the nucleus provides a better process for integrating the image of the quantum mechanical model with the “orbiting” electron model.


Single Electron Orbitals.png
Figure 6: Atomic Orbitals. http://chemwiki.ucdavis.edu/@api/deki/files/4826/=Single_electron_orbitals.jpg
ElectronOrbitals.png
Figure 7: Combined Atomic Orbitals http://static.ddmcdn.com/gif/atom-quantum.jpg



Repercussions of the Misconception:

Does it really matter that students are envisioning electrons orbiting the nucleus of an atom? There are other misconceptions with more damaging implications, including (Harrison & Treagust, (1996):

  • Since cells and atoms both have nuclei and outer shells, the nucleus can divide allowing atoms to reproduce. (One of the issues of having common language in biology and chemistry)

  • The electron shells are hard outer shells offering protection to the atom. (Similar to egg shells and snails.)

  • Electron clouds are like the clouds in the sky and contain embedded electrons like water drops. (This is similar to an even earlier model - J.J. Thomson’s Plum Pudding Model!)

If a middle school student is able to explain the location and charge of the subatomic particles, and that the mass of electrons is much less than the nucleus we have meet our goal. The misconception that the electrons are orbiting the nucleus is not interfering with the learning objectives. In high school a student needs to know how to use the periodic table to predict the energy levels of the electrons, the sublevels or orbitals of the electron density, and the outer valence electrons that are available for bonding (all taught using the Bohr model). If they can demonstrate that they know the relative location of the electrons, does it matter how they envision their motion? As an undergraduate college chemistry textbook states when explaining atomic orbitals and electron density “we are making no statement of how the electrons is moving within the orbital”(Brown, et al, 2009).

The Bohr model with the “orbiting” electrons does not need to be removed from school curriculum. Scientists use multiple models for teaching concepts and recognize the strengths and limitations of using each model. Students should not be deprived of using the tools that scientists use (McKagen et al., 2008). With proper teaching methods that allow for comparisons of atomic models students can come to understand the connections between the evolving models and refine their prior knowledge and misconceptions into scientific knowledge.



References:


Brown, T.L., LeMay, H.E., Bursten, B.E. (2009). Chemistry: the central science. Upper Saddle River, NJ: Pearson.
Buthelezi, T., Dingrando, L., Hainen, N., Wistrom, C., & Zike, D. (2013). Chemistry: Matter and change. New York: McGraw Hill.
Harrison, A. G., & Treagust, D. F. (1996). Secondary students' mental models of atoms and molecules: Implications for teaching chemistry. Science Education, 80(5), 509-534.
McKagan, S. B., Perkins, K. K., & Wieman, C. E. (2008). Why we should teach the Bohr model and how to teach it effectively. Physical Review Special Topics-Physics Education Research, 4(1), 010103.
Wilbraham, A., Staley, D.D., Matta, M.S., Waterman, E.L. (2012). Chemistry. Moston, MA: Pearson.




​Dogs Teaching Chemistry:


And for a quick smile – view two dogs demonstrating electron roles in chemical bonds:Dog.png
http://www.youtube.com/watch?v=_M9khs87xQ8&list=PL5E0C18D020E89EE8