Science Forums 2

[Moontanman]

Originally Posted by modest

Without relativistic effects, gold would be silver (in color), just like silver (the element).

Silver mostly doesn’t absorb photons of color. It absorbs ultraviolet photons and reflects all visible photons more-or-less equally—leading to its silver color. The ultraviolet frequency coincides with an electron jumping from one orbital to another. In the case of silver it’s from the 4d orbital to 5s.

Atomic orbital - Wikipedia, the free encyclopedia

Gold also could be predicted to absorb ultraviolet frequency when its 5d orbital electron jumps to a 6s orbital. But, the 6s orbital is contracted in gold enough to make the jump from 5d to 6s coincide with a blue photon (less energy than ultraviolet). When blue-frequency light is absorbed, all the redder colors are reflected which makes a gold color. The reason the 6s orbital is contracted while 5d is not is due to the shape of the orbital (or the probability of where the electron is). The s subshells get close to the nucleus of the atom while d does not. In gold, the 6s orbital gets closer (or, the electron has a higher probability of being closer) to the nucleus than does the 5d orbital (or electron).

This gives an electron in the 6s orbital a significant velocity compared to the speed of light (this is explained to some degree in the quote below). The greater the electrostatic charge of the nucleus, the grater the effective velocity. This is why a gold atom shifts the frequency enough to put it in the visible color range while a silver atom does not. Gold has a greater atomic number and more electro-positive protons in the nucleus. In other words, 6s valence electrons in gold are greater-affected by relativity than the s subshell valence electrons in lighter elements.



This site also offers a good explanation.



For the most part—no. The only other element heavy-enough with a valence s-subshell electron for this effect is cesium. As far as I know, it is the only other element besides gold that has a color significantly affected by relativity, giving it a blue spectral line and a slight gold hue. Mercury has two 6s electrons and is one proton heavier than gold. It's melting point is lowered from this relativistic effect which is explained here:

http://www.cengage.com/chemistry/boo....Ch07.CI08.pdf

~modest

So the color of copper has nothing to do with this effect?

Color

Copper just above its melting point keeps its pink luster color when enough light outshines the orange incandescence color.Copper has a reddish, orangish, or brownish color because a thin layer of tarnish (including oxides) gradually forms on its surface when gases (especially oxygen) in the air react with it. But pure copper, when fresh, is actually a pinkish or peachy metal. Copper and gold are the only two elemental metals with a natural color other than gray or silver. The usual gray color of metals depends on their "electron sea" that is capable of absorbing and re-emitting photons over a wide range of frequencies. Copper has its characteristic color because of its band structure. In its liquified state, a pure copper surface without ambient light appears somewhat greenish, a characteristic shared with gold. When liquid copper is in bright ambient light, it retains some of its pinkish luster.