In the Classroom edited by
applications and analogies
Ron DeLorenzo
Housing Electrons: Relating Quantum Numbers, Energy Levels, and Electron Configurations
Middle Georgia College Cochran, GA 31014
Anthony Garofalo Conard High School, West Hartford, CT 06107 In the quantum mechanical model of the atom, quantum numbers are associated with individual electrons in an atom so that each electron in its ground state is assigned a set of four quantum numbers. Students are taught that this way of modeling the atom makes no attempt to specify the position of an electron at any given instant. Instead, quantum mechanics deals only with the probability of finding an electron within a given region of space outside of the nucleus. The arrangement of electrons among the various probability locations of an atom is called the electron configuration of the atom. Electron configurations can be written using a special notation that tells the principal energy level, the type of sublevel, and the number of electrons in that sublevel. Students learn that these probability locations are also related to the energy level of each electron. Confusion is often generated as students attempt to relate quantum numbers to these probability locations, electron configurations, and energy levels. “Housing Electrons” attempts to combine these three concepts in a concrete, hands-on way for students. I constructed four model houses out of foam board (available at most art supply stores). The houses were divided, in turn, into levels and rooms within those levels. Each house represents the primary quantum number (n), each floor of the house represents the second quantum number (l) or sublevel, and finally, each room represents the third quantum number (ml) or orbital. (Refer to the template [Fig. 1] used to construct the house representing primary quantum number four.) I use two different-colored beads that are about one centimeter in size to represent electrons with opposite spins, thus introducing the forth quantum number (ms ). The houses are mounted on a 2-ft × 4-ft sheet of pegboard with each house being placed at a different level on an “energy level hillside”, so that the levels of the floors correspond to the energy levels of the sublevels
Figure 1. Template for constructing “House #4”.
presented by energy level diagrams typical of most texts discussing this topic (1). When the levels are arranged properly, the rooms of the houses, which correspond to orbitals, should align as do the boxes on an Aufbau diagram (2). I painted a hillside on the pegboard to enhance the analogy (Fig. 2). I have generated a transparency of the analogy to accompany class discussions (Fig. 3).
Figure 2. Classroom model of Housing Electrons.
Figure 3. Transparency master for Housing Electrons.
Vol. 74 No. 6 June 1997 • Journal of Chemical Education
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In the Classroom My students are now ready to start housing electrons. I remind them that it is the nature of things to seek the lowest possible energy. High-energy systems are unstable and unstable systems tend to lose energy to become more stable. In the world of the atom, electrons and the nucleus interact to make the most stable arrangement possible. We discuss the Aufbau principle, which states that electrons enter orbitals of lowest energy first. I mention that the various orbitals (rooms) within a sublevel of a principal energy level are always of equal energy. As students come up to take their turn in the activity, I also mention Hund’s rule, the Pauli exclusion principle, and how the range of energy sublevels within the principal energy level can overlap when appropriate. When a student has finished housing the electrons for one of the elements 1–20 (I hold off doing transition elements for the moment), I have another student go to the board and write the configuration based
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upon the model. We then compare our configuration with the accepted one. I have found that students respond exceptionally well to the housing model. It is concrete and enjoyable for them. It can be utilized to present most of the theory associated with the generation of electron configurations. I have used the model to illustrate the 2n 2 formula as well as to discuss and show excited electrons. Substitute jelly beans for the beads and you will have every hand in the class raised as volunteers get to snack on the “electrons” they have housed. Literature Cited 1. Dorin, H.; Demmin, P. E.; Gabel, D. L. Chemistry. The Study of Matter; Prentice Hall: Englewood Cliffs, NJ, 1992; p 341. 2. Wilbraham, A. C.; Staley, D. D.; Simpson, C. J.; Matta, M. S. Chemistry; Addison-Wesley: Reading, MA, 1993; p 251.
Journal of Chemical Education • Vol. 74 No. 6 June 1997
