ORBITAL MODELS GERALD W. A. FOWLES University of Southampton, Southampton, England hypothetical bouudary surface enclosing say 90 per cent of the charge cloud, but balloons are notoriously shortlived and are not usually of the required shape (unless a group of balloons is used). Plaster of Paris models are possible, but lighter and far more robust orbitals can be modeled from papier-m8chd. Photographs of some such models used by the author in teaching valence a t Southampton are shown in the i figures. These models have been made approximately .i to scale in agreement with Pauling's urotrusiou values': An s orbitar is thus a sphere of :-in. radius (unit pro.. trusion), while each lobe of the p orbital is about 1.7 in. in length. The orbitals have been distinguished by the following color scheme: -."--..~ ...-,..,,.., Simple Orbitals. The s orbitals are orange. - . .p orbitals Figure 1 green,-and d orbitals yellow. &/6 lo i i g h l ; r o r h i f n l , 11 n r h i t r l , and d u r h i t z l Hybridized Orbitals are all given a basic black color, and are painted with rings the color and number of which correspond with the orbitals contributing to the M A N Y students find difficulty in appreciating the directioual properties of atomic orbitals. They are told, hybrid. E. g., sp hybrids have one orange and one green ring, spa hybrids have one orange and three green for instance, of a p orbital which is symmetrical about rings, and d2sp3 hybrids have two yellow, one orange, the x, y, or z axis, and hybridized orbitals which may and three green rings. be linear, trigoual, tetrahedral, planar, or octahedral, to Models of simple molecules can also be made, when name only the more common; but despite tolerable the orbitals will be molecular, embracing both the blackboard sketches, the three-dimensional concept These molecular orbitals are divided remains vague, and needs focussing by means of suit- bonded atoms. able solid models. How, then, can such models be made? L p,,,,,,, L., -xature f, the chemical ~ ~ cornell ~ Balloons may, of course, he used to illustrate the University Press, 1945, p. 78.
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by a broad white band, and each half is painted ac- with a coarse file or with a grind stone. A hole (of dicording to the type of atomic orbital which originally ameter slightly less than that of the wire) is drilled in contributed t o the molecular orbital. Thus r molecn- the orbital, which is then forced onto the framework. lar orbitals are painted green with a white central Since the metal framework is made first, some orbitals band, since they are formed from p atomic orbitals. in the molecular models cannot be forced into position Figure 3 shonrs photographs of models of the ethane, in this way, but must first be cut longitudinally and ethylene, and benzene molecules, illustrating u, local- then placed around the wire and bound together with fine copper wire. When the whole model has been ized a,and delocaliwd ?r orbitals respectively. The skeleton framework for any of these models is assembled it is given a basic coating of cheap paint (to made from lengths of piano wire or welding rod (18 remove the absorbent properties of the paper), painted s.w.g.) silver soldered together and bent to the required appropriately, and given a coating of clear varnish. angles. Papier-miichd can readily be made by pulping ACKNOWLEDGMENT old newsprint (not glossy magazines); the pulp is My thanks are due t o Mr. E. W. Balson, BSc., nrho squeezed by hand to the approximate shape, allowed t o dry slowly, and the inevitable bumps are then removed prepared the photographs for the figures.
