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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 12 Issue 3 (2007) pp 142-149

Relativity In Chemistry

M. Mahdi Najafpour

Dorna Institute of Science, 83 padadshahr 14 St, Khozestan, Ahwaz, Iran, mmnajafpour@yahoo.com
Received November 18, 2005. Accepted September 8, 2006.

Published online: 4 June 2007

Abstract. Einstein's Special Theory of Relativity describes the motion of particles moving at close to the speed of light. In fact, it gives the correct laws of motion for any particle. This doesn't mean Newton was wrong, his equations are contained within the relativistic equations. Newton's "laws" provide a very good approximate form, valid when speed is much less than the speed of light. For particles moving at slow speeds (very much less than the speed of light), the differences between Einstein's laws of motion and those derived by Newton are tiny. That's why relativity doesn't play a large role in everyday life. However relativity is important in chemistry. It is an irony of history that in 1929 Dirac himself, one year after publishing the Dirac equation and just before stating “Dirac’s dictum,” thought that relativistic effects would be “of no importance in the consideration of atomic and molecular structure and ordinary chemical reactions” because the average valence-electron speeds are small. The reason he was wrong is twofold:(i) the valence s and p electrons have high speeds in the inner parts (in other words, orthogonality constraints against core states) and (ii) there are indirect relativistic effects, the former being important for the s and p shells and the latter being important for the d and f shells.

Key Words: In the Classroom; phyiscal chemistry; quantum

(*) Corresponding author. (E-mail: mmnajafpour@yahoo.com)

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Issue date: June 1, 2007

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