Ionocovalency explains Color of Copper, Silver and Gold

Ionocovalency explains Color of Copper, Silver and Gold [1]

Yonghe Zhang

American Huilin Institute http://www.amhuilin.com  

 

Relativistic effects only said: “the s orbitals of the heavier elements become more stable than otherwise expected” [39]. Obviously, the relativistic effects can give a qualitative overview on the color of gold and silver, but has nothing to do with the color of copper.  

Ionocovalency can expain quantitatively the color of copper, silver and gold. In IC model, the phenomenon of “the Color of Copper, Silver and Gold” is attributable to the fact that their bond structure is controlled by their spatial covalency and IC potential energy, and also related its Group specific effects: n*, z*, rc, rc-1, Iav.

 

As Table 3.8 shows that with the increase of the s orbital contracts the outer d orbitals expand and their ionicities Iav are decreased from Cu3+ via Ag3+ to Au3+, however, with the increase of their effective principle quantum number n* the covalency rc-1 decrease from Cu3+ to Ag3+ but increase from Ag3+ to Au3+ that causes the spatial covalency n*rc-1of Cu3+ higher than that of Ag3+ but close to Au3+, leading to same trend in ionocovalency.

This quantitative trend in their structure and energy nicely reflect their character of color. Copper and gold are the only two elemental metals with a natural color other than gray or silver which depends on their ionic delocalizing property of “electron sea” that is capable of absorbing and re-emitting photons over a wide range of frequencies. Copper in its liquified state, a pure copper surface without ambient light appears somewhat greenish, a characteristic shared with gold.

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 Table 3.8 Atomic Parameters of Cu, Ag and Au

Cations

Cu3+

Ag3+

Au3+

n*

3.45

3.85

4.36

z*

4.349

4.81

5.297

rc

1.11

1.339

1.336

rc-1

0.901

0.747

0.749

n*rc-1

3.108

2.875

3.263

Iav

21.610

21.227

20.08

XIC

1.885

1.867

2.021

IC

3.918

3.592

3.965

 

[1] Zhang, Y. Ionocovalency and Applications 1. Ionocovalency Model and Orbital Hybrid Scales. Int. J. Mol. Sci. 2010, 11, 4381-4406

 

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