Atomic and Molecular Models
G. Olof Larson Westminster College solt Lake C i t y , utoh
Made from Vinyl Covered Wire
This paper presents a series of scalar models made from vinyl covered wire. They feature the skeletal stmcture of molecules, and two types show atomic dimensions in color. The conversion of conventional wooden or rubber balls into scalar models of this latter type is also discussed, along with a method for showing hindered rotation in single bonds of such models.
These models are made to scale (i.e., tube lengths indicate covalent radii) and conventional color coding is used for carbon (black), oxygen (red), nitrogen (blue), hydrogen (white), etc. Atom models are connected by pieces of wire inserted in the tubes (Fig. 3). A thin
Dreiding Type Models
The simplest atomic models of the series are made by joining pieces of vinyl covered wire, in which the wires have been partly pulled out of the sleeves to give "jack and plug" ends. Joining is easily accomplished by melting the plastic insides of two appropriately bent pieces with a soldering tip just prior to bringing them together.'
Figure 1.
Diamond lattice.
Figure 2.
Glucose.
The resulting "Dreiding type"2 model is convenient for representing macromolecular systems, or models which emphasize only the molecular carbon skeleton. Since both black and white vinyl can be assigned to represent carbon (with hydrogen nuclei a t the "open" ends), models can be constructed which show a particular skeletal feature in black against a contrasting framework,. e.g.. - . Ce "chair" rings - in diamond lattice (Fig. I). Short vinyl sleeves over the bare wire ends improve the appearance of this type of model, but red oxygen and blue nitrogen are obviously unsymmetrical in the bends. Figure 2 shows a model of glucose in which the white sleeves represent hydrogen.
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Figure 3. Scalar vinyl wire model$. Upper left: carbon ond nitrogentetrahedra. Upperright: oxygen (rp2-rp3compromi~e form1 ~p2nitrogenondcorbon. Topcenter downto left: nitrile, carbonylr. ond C-C double bonds from both #8 and $1 2 vinyl wire.
coat of vinyl cement3 on the wire connectors gives greater stability to large assembled models, attended by decreased rotational freedom in the bonds. Models of sp3 carbon and nitrogen (both amino and quaternary ammonium) have normal tetrahedral angles between the vinyl tubes. ~Iodelsof s p Z carbon and nitrogen (amido, imido, imino, oximino) are planar, with one piece open to 120' and the other piece bent double. Aromatic carbon and nitrogen are also made from sp2 models, but they need special tailoring to give ring symmetry. Linear (sp) carbon and nitrogen are made from specially preshaped pieces (Fig. 4). An oxygen model is similar in shape to an sp2 carbon, but with one piece bent to 110' and the other only partially closed. In this compromise form, it can be nsed either as divalent oxygen, or as sp2 carbonyl oxygen. A single piece of white vinyl tubing, with wire connector cemented in, is used as a hydrogen model (length equal to covalent diameter). The open end of the tube is nsed with a special connector for representation of hydrogen bonding. Models of larger monovalent atoms are made like hydrogen, or they may be made like oxygen or nitrogen, in which the unlinked tubes represent unshared electrons, and suggest additional space requirements. Fnrthermore, models of hydrogen and other peripheral
Color Coded Scalar Models
More symmetrical atomic models are made from lengths of vinyl tubing in which shorter pieces of wire are first centered and then bent to the proper angle. The bent pieces are fused together as described above. 'Details of procedure and suggested dimensions for different sizes of vinyl covered wire will he supplied by the author to
Siggure4. Scolm molecvlor models. lJpper left: nicotinic ocid. Upper right: 2-methylacrylonitrile. Lower left: cyclobutanol. Lower right: 4-cyclopentenone.
int,emt,ed r e d e m
2 D ~ ~ A.,~ U.~ S.~ Patent ~ o 2,974,425 , (1961). See also FEISER,L. F.,J. CHEM.EDUC.,40, 457 (1963). s"Magic Plastic Patch," made by Magic Iron Cement Co., Inc., Cleveland 27, Ohio, is very satisfactoryfor this purpose.
Volume 41, Number 4, April 1964
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Figure 5. Scolor model of herone, showing optional useof von der Wools hemispheres on hydrogens.
Figure 6. Model of cyclooctone made of portioily converted wooden balk. Maximum length wire connectors ore used to stobilire bond angles during manipulation of model.
Figure 7. Converted ball models. Center: ethone. Left: methane. Right: ethonol. The latter two exampler demonstrate how both covolent and nonbonded radii of h y d r o gen ore shown together.
atoms can be augmented with plastic foam hemispheres to show interference radii4 or pi orbitals5 (Fig. 5). Scalar models of coordination metal atoms can also be made of fused vinyl tubing, or by cementing 4 or 6 properly oriented vinyl tubes into plastic foam balls.
are at the centers of their respective models. When the unconnected "space indicator" tubes of peripheral atom models are fitted with "van der Waals" accessories, the inner, skeletal stn~cturecan still be seen (Fig. 7).
Rejuvenation of Ball and Stick Sets
Hindered Rotation
Appropriate lengths of colored vinyl tubing (wire removed) are cemented into existing holes of balls, and the wire is used to make connectors. A range of bond flexibility can be achieved, depending on the length of wire used. The longest possible connector is best for use in models which demonstrate conformational changes in large ring systems. With short connectors, models of small ring systems, double bonds and even triple bonds can be made, which are more satisfactory than those made with conventional springs (Fig. 6). Besides their low cost, the converted hall and symmetrical vinyl wire model systems combine many advantages of both the "skeletal" and "solid space" types. Covalent atomic dimensions are indicated along bonding axes. Color coding helps the viewer to "fill" solid angles in the skeletal system. All atomic nuclei
A further refinement, especially for the converted hall models, is the representation of hindered rotation by using triangular connectors in triangular vinyl tubes. A slightly oversized wire with tapered, triangular cross section is forced into a vinyl tube with its edges in line with the other tubes in any atom model. The wire is heated until the plastic relaxes and is then cooled in place. When removed, it leaves a triangular hole in the plastic. Special wire connectors, also with triangular cross sections, have a sharp GO0 twist a t the center. Hindered rotation results from a bond made up of triangular components, and adjacent atom models come t o rest with their groups properly staggered. (Of course, regular connectors can still be used in the triangular tubes.) By the use of unsymmetrically shaped connectors in correspondingly shaped tubes, more subtle group interactions can be represented in special problems of conformational analysis.
'KOOYMAN, E. C., J. CBEM.EDUC., 40, 204 (1963). "BRUMI~IK,
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G . C., J. CBEM.EDTIC., 38, 502 (l9G1).
Journal of Chemical Education
