applications and analoqiss Some Analogies for Teaching Atomic Structure at the High School Level Ngoh Khang Goh, Lian Sai Chia, and Daniel Tan Nanyang Technological University Republic of Singapore
Atomic structure is a n important topic in high school chemistry, hut the concepts involved in this topic are quite abstract and difficult for students to comprehend. Many experienced teachers have found that using some analogies that appeal to students' daily experiences or imaginations usually help them in understanding certain science concepts. Recently, Chiang and Tseng ( 1 ) suggested, in this Journal, a very useful and interesting aid for teaching the theory of atomic structure. Later, Grenda (2)also proposed a simple but excellent mnemonic device for teaching electron configuration. Apart from these, very few analogies or ideas for teaching atomic structure have been published. For this reason, we would like to share our experience and add to the pool. An Analogy for Orbital
An orbital is defined a s a region in space in which there is a high probability of finding a n electron. An analogy for an orbital is the possible location of a student based on his or her timetable. For example, according to the timetable, on Monday a t 9.00 am, a student has to be in Lecture Room 1for a chemistry lesson. One can say that, over a period of weeks, there is a high probability that this student will be in Lecture Room 1a t that time on that day. However, one cannot be 100% sure that this student will be there because he or she may be absent from school on that day. One also usually cannot predict exactly where the student will sit in the lecture room, but one can say, with a high probability that this student will be within the confine of the lecture room. This analogy describes a n orbital fairly well, because it takes into consideration the probability and region of space in the definition of a n orbital.
edited by RONDELORENZO Middle Georgia College Cachran. GAS1014
An Analogy for Hund's Rule
Hund's rule states that all the orbitals of a subshell in a n atom must be occupied singly by electrons before they can be occupied in pairs. Similarly, if a bus is full of empty seats, people who are strangers normally would occupy all the empty seats first. They seldom would share a half-occupied seat with a stranger if there are empty seats available. If a stranger decides to share a half-occupied seat, the other passenger will get excited, feel rather uncomfortable, and wonder about the intruder's intentions. In other words, the first passenger will be in a disturbed state or "excited" state, and wish that the second person will move away. Thus, the analogy gives students a feel of both Hund's rule and excited state. An Analogy for the Four Quantum Numbers An address of a tenant is a good analogy for the four quantum numbers (Fig. 1). The address consists of street name, house number, unit number, and the tenant's name. When one knows these four pieces of information, one can find the tenant. This analogycan be represented using sets, narrowing the location of the tenant down from street name to his or her name. Similarly, the students a t high school level can be told that the quantum numbers give the address of a particular electron. The principal quantum number (n) indicates which shell the electron is in, the subsidiary quantum number (1) indicates which subshell, the magnetic quantum number (m) gives the orbital orientation (or shape) of the electron, and the spin quantum number (s) gives the spin of the electron. Again, the position of the electron is narrowed down a s we go from the principal quantum number to the spin quantum number. This analogy is illustrated in Figure 2. One must remember to tell students that no two electrons in the same atom can have the same four quantum numbers (Pauli's Exclusion Principle). This is just like no two tenants can have exactly the same address (including tenant's name). -
principal ~uantumNo.
House Number
Subsidiary Quantum No.
Unit Number
- -
--
-~
Magnetic Quantum No. Spin Quantum Number --
- -~
~
Street Name
~
-
Figure 1. Address of a tenant.
Figure 2. Address of a particular electron Volume 71
Number 9 September 1994
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The above-mentioned address idea is quite simple but useful, and the nested rectangles make the concepts concerned more concrete and easier to visualize. Concluding Remarks Each of the above analogies stresses the particle nature of electron interactions. As a note of caution, it is worthwhile to remind teachers and students the unique waveparticle duality that electrons exhibit. Teachers and stn-
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dents also should realize that an analogy never will be identical to a concept. There are some differences between them, and only certain aspects of the analogy are similar to that of the concept. Literature Cited I. chiang, H. c.;~ s e n gc, H.J. chom. E ~ U C .1 ~ 8 4 . 6 1 . 2 1 6 . 2. ~ r m d aS. , C. J. chem. E ~ WIS=, . 66,697.
