Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Shadow on September 25, 2014, 05:16:00 AM

I see that relativistic effects explain many important things. When do relativistic effects appear in the periodic system, why and how?

Generally not until the late transition metals. A common explanation for why relativistic effects occur at very high Z numbers is that when the nuclear core charge increases, so too does the average speed of orbiting electrons because the Coulombic force magnitude becomes large. At some point the electronic speed is sufficiently close to the speed of light that relativistic effects can no longer be ignored. Be aware that there's no hard and fast cutoff for when this happens. Relativistic effects are treated as a perturbation, and they could be applied even in hydrogen if you wanted to. The effects are not great enough to observe really until about period six, in elements like mercury and gold.

What equation describes that?

Not everything can be described by a simple equation. You can probably find a textbook on relativistic quantum mechanics if you're really interested. Or you can start here: http://en.wikipedia.org/wiki/Relativistic_quantum_mechanics. I wish you luck. :)

first thing: "relativistic effect" is a really strange term because it means "everything we cannot describe by the schrÃ¶dinger equation but need the DIRAC EQUATION". so it's a completely theoretical term.

also spin emerges naturally from the relativistic treatment of the electron.

This paper from Pitzer is a good beginning place to begin on this topic. I highly recommend it and it was a reference I used in my thesis.
Relativistic effects on chemical properties by Kenneth S. Pitzer Acc. Chem. Res., 1979, 12 , pp 271â€“276. (http://pubs.acs.org/doi/abs/10.1021/ar50140a001)

Mitch,
That's a great article. I read it first sentence to last. Thanks for sharing it.

I'm glad you like it.