A Mnemonic for Predicting Electronegativity Values I t has been more than 50 years since Pauling introduced the idea of 2.0 2.5 3.0 3.5 4.0 electronegativity ( 1 ) as "the power of an atom in a molecule to attract elec' B F trons t o itself' (2). The electronegativity concept is very useful in determining bond type and character, approximating bond energies, and rationalizing similarities in chemical behavior and reaction mechanisms (3). The difficulty with the electronegativity concept is that i t is not a property of an isolated atom but rather of an atom in a specific valence state combined in a molecule (4-6). Consequently, electronegativity is neither an observable, empirical quantity, nor is it particularly amenable t o theoretical calculations (6,7). Some of the difficultieswith the electronegativity concept have been mentioned in a recent paper in THIS JOURNAL(7). I.' This article presents an easy-?-use mnemonic with which relatively accurate electronegativity values for the representative elements can be I Te obtained. Table 1 shows the right side of the periodic table. Note that the third row elements ax shifted one space to the left. In this modified repre1.6 ln\sn\sb sentation of the periodic table, elements along the diagonals will have apTI Pb Bi proximately equal electronegativity values. Taking either 2.5 as the electronegativity of carbon or 4.0 for fluorine as a reference, and reading across the top, there is a 0.5 difference in electronegativity values between each pair of diagonals. Reading down the left side, there is a 0.1 difference in electronegativity values between each pair of diagonals. T o use the table, take the corner diagonal (B,P,As,Te; x = 2.0) as the startingpoint and simply count diagonals. Thus, if the electronegativity for bismuth is desired, count down two diagonals, then x = 2.0 - 0.2 = 1.8; for oxygen, x = 2.0 3(0.5) = 3.5. The metallic elements do not follow such readily predictable trends. However, very good results are obtained with the following approximations: H = 2.0, Group I or I1 = 1.0, Sc-Mn = 1.6, Fe-Cu = 1.8.
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Literature Cited (1) (2) 131 141 (51
Pau1ina.L..J. A m r . Cham. Soc.,S4,3570(1932). Pauling, L., "Natureofthe Chemical Bond," CorneUUniv. Press, Ithsea, N.Y. 1939. Chapter 2. Moel1er.T.."lnorganicchemiatry,"John Wileysnd Sons. New York, 1982, Chapter 2. Mu1liken.R.S.. J. Chem.Phya.,3,573 11935). Pearson, R. G..J Chom. Phya.. 17,969 (1949). ( 6 ) Prichsrd, H. 0.. and Skinner, H.A,, Chem. Re"., 55,745 (1955). 17) Barhe, J . , d C~~~.E~~~..s0,640(1983).
G. Mattney Cole, Jr. Colaado School of Mines Golden. C 0 80402
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