Computer Program for Calculation of Charge Distributions in Molecules
A Computer Simulation of a Kinetics Experiment
Sandersonl has proposed an eleetronegativ/ty scale based on values obtained using the relative compactness of t h e electronic clouds of each of the elements. Using these values, Sanderson describesZa method for calculation of the charge on each of the atoms in any given molecule (organic or inorganic). The charge distributions have been found to he in reasonable agreeinent with those obtained by extended-Huckel c a l ~ u l a t i o n s .These ~ charge caleulations are useful in gaining an insight to the electron distributions in molecules. This method has an added advantage aver other methods in that the Sanderson method is faster and less expensive. Also, these calculations can be carried out by hand using only a table of logarithms. The program to calculate charge distributions is written in Basic Fortran IV and is suitable for use on a n IBM 1130. Storage requirements are minimal. The input for the program consists of the svmbol of the element and the number of atoms of that element present in a given rnuleculr The output cmslsts of the mput data as well as the calculated charges. A prnmnm lirthg, snnaplc output, handworked example and other information are available
The inclusion of a few computer simulations in a physical chemistry laboratory program has several potential advantages. The time required for data collection is so short that the student can give most of his effort to planning significant aspects of the experiment and to interpretation of the results. In addition, experiments which require equipment not usually available to undergraduates or highly skilled techniques are made accessible. A program to simulate a study of the rate of the reaction,' (HzO)sCrBr2+ U3+(aq) Crzt(aq) + U4+(aq) Br-(aq), has been developed and run on the Culler-Fried time sharing system a t the University of California, Santa Barbara. After studying an introduction to the oroblem. the student chooses the concentrations
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obtaining one or mare of nine different plots of the data. ~ t numa her of points in the simulation a user who enters unrealistic experimental conditions will receive a cautionam mdsaee. .. . and the oregram w l hranrh to an earlier locct~unto recwve new input The pocl ior the student is to derernn~nrthe form the rate law and the value of the rate ronstcnr at 2S.C through use of tho c x w s s reagent method, initial rates, or trial of integrated rate equations. Complete documentation, including handout to students, brief and comprehensive flowcharts, and program listing, is available from the author.
'Sanderson, R. T., J. Chem. Educ.. 29. 539 (1952); 31, 2 (1954); 31,328 (1954); 32,140 (1955). ZSanderson, R. T., "Chemical Periodicity," Reinhald Publishing Co., New York, 1960, Ch. 3, pp. 37-55. Sanderson, R. T., "Inorganic Chemistry," Reinhold Publishing Co., New York, 1967, Ch. 6, pp. 69-88. Sanderson, R. T., "Chemical Bonds and Bond Energy,"Aeademic Press, New York, 1971, Ch. 2, pp. 13-26. 3Stoklosa, H. J., Wasson, J. R., Montgomery, H. E., unpublished results.
Wang, R. T., and Espenson, J. H., J. Amer. Chem. Soc., 93, 1629 (1971).
Henry J. Stoklosa
William C. Child, Jr.
University of Kentucky Lexington, 40506
290
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Journal of Chemical Education
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Carleton College Northfield, Minnesota 55057
