In chemistry, CPK coloring is a popular color convention to distinguish atoms from various chemical elements in molecular models. The scheme is named after the CPK molecular model designed by chemists Robert Corey and Linus Pauling, and enhanced by Walter Koltun.
Video CPK coloring
History
In 1952, Corey and Pauling published descriptions of proteins and biomolecules modeling the space they had built at Caltech. Their model represents the atoms by a multicolored wooden ball, painted in different bright colors to show each chemical element. Their color schemes include
- White for hydrogen
- Black for carbon
- Blue sky for nitrogen
- Red for oxygen
They also built smaller models using plastic balls with the same color scheme.
In 1965 Koltun patented an improved version of Corey and Pauling modeling techniques. In his patent he mentions the following colors:
- White for hydrogen
- Black for carbon
- Blue for nitrogen
- Red for oxygen
- Solid yellow for sulfur
- Purple for phosphorus
- Light, medium, dark, and dark green for halogens (F, Cl, Br, I)
- Silver for metal (Co, Fe, Ni, Cu)
Maps CPK coloring
Typical task
Typical CPK color assignments include:
Some CPK colors refer mnemonically to the color of pure elements or important compounds. For example, hydrogen is a colorless gas, carbon as charcoal, graphite or coke is black, common sulfur is yellow, chlorine is greenish gas, bromine is a dark red liquid, iodine in ether is purple, amorphous phosphorus is red, rust is dark orange- red, etc. For some colors, such as oxygen and nitrogen, the inspiration is less clear. Perhaps red for oxygen is inspired by the fact that oxygen is usually necessary for combustion or that oxygen-carrying chemicals in blood, hemoglobin, bright red, and blue for nitrogen by the fact that nitrogen is a major component of Earth's atmosphere, which seems to be a sky-blue human eye.
Modern variant
The following table shows the colors defined for each element by some popular software products. The C column is the original assignment by Corey and Pauling, and K is a Koltun patent. The J column is the color scheme used by Jmol molecular visualization. The R column is the scheme used by Rasmol; when two colors are displayed, the second applies to version 2.7.3 and later. All colors are approximate and may depend on display hardware and display conditions.
See also
- The ball-and-stick model
- Molecular graphics
- Software for molecular modeling
References
External links
- Physical Molecular Model
Source of the article : Wikipedia
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