Conceptual Problems Associated with d-Orbital Models
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Over the past three y e m work has been done to isolate and rectify the problems of understanding snd lemning experienced by students when first confronted with the d-orbital \ I situation and with crystal field theory. The main oonceptual difficulties were shown t o be as follows. (a) Students brought up with the useful concept of the spherical atom found themselves up ageinst an apparently nowspherical model. Although they were prepared to accept the new model, there persisted an uneasy gap in the development of their thinking. (h) Since d-orbital models were usually exhibited as five separate entit,iesside by side, the superimposition of them was made more complex far the student having difficulty in seeing and thinking in three dimensions. This situalion was even more acute when students were obliged to work from illustrations in a book rather than with models. (o) Arising from the difficulties mentioned above, students had trouble in visualizing the situation of a. speoies in an octahedral field undergoing splitting of the d-orbital energy levels. ~i~~~~ I . sep. ~i~~~~ 2. CornTo overcome these problems, the model shown in the orate d orbit- bined d orbit.Is. d6. illustrations was devised. Its main features me as follows. (1) All the separate d-orbital models yhare a common vertical axis making their superimpmition easier (Fig. 1). (2) The center portion of the d,Porbitrtl is used sr a. support far a, complete set of axes on to which the other four d-ol.hititls can be transferred and built up to show that spherical symmetry still exists (Fig. 2). (3) The d,LV2orbitalcen be superimposed on the d,20rbitd and then surrounded by "atoms" on the z,y, and z axes to give an octahedral pattern. Theve two orbitals are seen to be pointing towards "electron-rich" species. The remaining three orbitals can then he added and be seen to point between the "electronrich'' species thus giving rise to splitting of the d-orbitals into two of higher energy than the other three. The lobes can he slid on and offthe axes freely but those on axes minting- downwards are held by n slight bend in the wire. Acknowledgement is made to Mr. T. Littlefair of the High School, Stirling, Scotland, who const,ructed the model.
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References to Olher d-Orbital Models
(1) DOUGLAS, B. E., J. CHEM.EDUC.,41,40 (1964). (2) B n ~ l i RW. , L., J. CHEM.EDUC.,45,135 (1968). (3) N O R ~ U RA. Y ,H., Education in Chemistry, 5,31 (1968).
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