Question

Gold is a very unreactive element. It only bonds with strong chemicals. As Gold has a single outer S shell electron it should be reactive. Why isn't it?

Answer 1

The electron configuration of gold is:

`[Xe] 4f^14 5d^10 6s^1`

Gold is also the go-to element when thinking about relativistic effects. Its `6s` electron moves very quickly. Gold's `1s` electron moves at around `57.7%` the speed of light, so the `6s` electron, probably quite fast.

This high speed `6s` electron is then more attracted to the nucleus than we expect, and the `6s` orbital contracts (relative to without relativistic effects). To maintain orthogonality of all orbitals, the core `5d` and `4f` orbitals expand.

Thus, the `6s` electron becomes less accessible for bonding than we expect and fairly dissimilar in energy to many incoming reactants, to such an extent that gold is mostly unreactive.

Another take on this question is here.