The double quartet or electronic repulsion theory of chemical bonding which was proposed originally by Linnettl and extended recently by Luder2 has appeared in chemistry textbooks, both a t the freshman levela and above.& I n the present* tion of this approach it is often difficult to accustom students to think in terms of single electrons rather than electron pairs with which they are familiar from the Lewis theory. This task is made more difficult by the lack of suitable models to show the very important
o
b
c
Figure 1. Double quartet models for eight electrons around a single nucleur: a, no electron$ clors.poired in space (He atdm); b, 2 electrons and 7 electrons of like spin around two nuclei. By combining any pair of these three electron sets, it is possible to represent diatomic assemblies containing from 10 to 14 valence electrons. Thus, the superposition of 2(e), possessing 5 electrons, with itself would produce a molecule of 10 electrons, (N2),vith a 6 electron bond between the nuclei. Similarly, combining 2(a) with i electrons of like Spin 2(,.) with 5 electrons of the opposite spin would yield a 12 electron molecule (Or). which has a 4-electron bond between the nuclei and is paramagnetic owing to the excess of 2 electrons of one spin state, in agreement with the ground state configuration of oxygen. Other chemical species can be represented in a likemanner,
'LINNEV, J. W., J . Am. Chen. Sac., 83, 2643 (1961). LINJ. W.. "The Electronic Structure of Molecules." John , LUDEE,W. F., J . Chem. Ed., 44,206 (1967). S S ~M. ~J., AND ~ PLANE, ~ ~ R. , A,, "Chemistry: Principles and Properties," McGraw-Hill Book Co., New York, 1966, p. 55. 'DOUGLAS,B. E., AND MCDANIEL, D. H., "Concepts and Models of Inorganic Chemistry," Blaisdell Publishing Co., .. New York, 1965, p. 67. NEW.
Figure 2. Double quartet models for diatomic orrernbliea a. 7 electrons of like spin; b, 6 electrons of like spin; c, 5 electronr of like spin.
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Journal of Chemical Education
