The color of gold and relativity

[Moontanman]

Moderation Note: The following 5 posts were split from Origin of the Universe,,,,Bang or no Bang in favor of having their own topic in this thread

 

It really does. The same theory that we use to explain the behavior of satellites in orbit and the color of gold metal (i.e. relativity) also explains the history of the cosmos. If the history of the universe is significantly different than we think then we would need a new theory that works with local and cosmic observations.

 

~modest

 

Modest, how does relativity explain the color of gold and does it explain the colors of other metals?

[modest]

Modest, how does relativity explain the color of gold

 

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.

 

Q26. If the electron cannot be localized, can it be moving?

 

In its lowest state in the hydrogen atom (in which l=0) the electron has zero angular momentum, so electrons in s orbitals are not in motion. In orbitals for which l>0 the electron does have an effective angular momentum, and since the electron also has a definite rest mass [math]m_e[/math] = 9.11E31 kg, it must possess an effective velocity. Its value can be estimated from the Uncertainty Principle; if the volume in which the electron is confined is about [math]10^{-10} \ m[/math], then the uncertainty in its momentum is at least [math]h/(10^{10})[/math] = 6.6E–24 kg m / s, which implies a velocity of around 107 m / s, or almost one-tenth the velocity of light.

 

The stronger the electrostatic force of attraction by the nucleus, the faster the effective electron velocity. In fact, the innermost electrons of the heavier elements have effective velocities so high that relativistic effects set in; that is, the effective mass of the electron significantly exceeds its rest mass. This has direct chemical effects; it is the cause, for example, of the low melting point of metallic mercury and of the color of gold.

 

Quantum Primer

 

This site also offers a good explanation.

 

and does it explain the colors of other metals?

 

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/book_content/0547125321_zumdahl/chemical_connections/Zumdahl.8e.Ch07.CI08.pdf

 

~modest

[Moontanman]

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/book_content/0547125321_zumdahl/chemical_connections/Zumdahl.8e.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.

[modest]

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

 

Nope. The transition energy between copper’s 3d and 4s orbital is small without the relativistic effects described in the links above. Copper’s nucleus (atomic number 29) is not electro-positive enough to significantly, relativistically contract the 4s orbital.

 

I realize you asked this question before at Hypo in the technology news forum regarding this webpage and you got a different answer. But, looking at that page closely (it’s in question / answer format), it appears to me only to attribute relativistic effects to gold and not copper, saying “The 3d, filled in copper, is less shielded by the s and p subshells... Now when you get to gold (5d) relativistic effects become important.”

 

The relativistic effects section of wiki's article on atomic orbital might be illuminating.

Examples of significant physical outcomes of this effect include the lowered melting temperature of mercury (which results from 6s electrons not being available for metal bonding) and the golden color of gold and caesium (which result from narrowing of 6s to 5d transition energy to the point that visible light begins to be absorbed).

 

~modest

[Moontanman]

Nope. The transition energy between copper’s 3d and 4s orbital is small without the relativistic effects described in the links above. Copper’s nucleus (atomic number 29) is not electro-positive enough to significantly, relativistically contract the 4s orbital.

 

I realize you asked this question before at Hypo in the technology news forum regarding this webpage and you got a different answer. But, looking at that page closely (it’s in question / answer format), it appears to me only to attribute relativistic effects to gold and not copper, saying “The 3d, filled in copper, is less shielded by the s and p subshells... Now when you get to gold (5d) relativistic effects become important.”

 

The relativistic effects section of wiki's article on atomic orbital might be illuminating.

 

~modest

 

So I guess my next question is why copper is pinkish in color and not silver or grey like almost all other metals.

[modest]

So I guess my next question is why copper is pinkish in color and not silver or grey like almost all other metals.

 

I think the 3d, 4s transition energy is small-enough to coincide with visible light in copper (much like gold). Copper is kind of special in its electron configuration and position on the periodic table because 3d electrons have more energy than 4s electrons in elements lighter than copper while 4s has more energy in elements heavier than copper. This has to do with the different quantum numbers n and l (lowercase L). A larger value n and a larger value l both mean more energy for an electron, but which is the dominant factor depends on if the element is greater or less than copper in atomic number.

 

This is not a relativistic effect, as with gold and cesium.

 

~modest