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In chemistry, CPK coloring is a popular color coding that is used to distinguish the different types of atoms.

Origin of the Concept

In 1952, Robert Corey and Linus Pauling published a description of space-filling models of proteins and other molecules that they had been building at Caltech. Their models represented atoms by using hardwood balls, painted in different bright colors to indicate the respective chemical elements. Their color schemes included:

  • White for Hydrogen
  • Red for Oxygen
  • Blue for Nitrogen
  • Black for Carbon

Typical color assignments

Typical CPK color assignments include:

Color Element
     white Hydrogen (H)
     black Carbon (C)
     blue Nitrogen (N)
     red Oxygen (O)
     green Chlorine (Cl)
     yellow Sulfur (S)
     violet Alkaline metals (Lithium, Sodium, Potassium, etc.)
     gray or silver Titanium (Ti) and most metals
     dark red Bromine (Br)
     dark violet Iodine (I)
     cyan Noble gases* (Helium, Neon, Argon, and Krypton, etc.)
     orange Phosphorus (P)
     dark green Alkaline earth metals (Beryllium, Magnesium, Calcium, Strontium, etc.)
     dark orange Iron (Fe)
     pink other elements

References

http://aip.scitation.org/doi/10.1063/1.1770803

Notes

* Noble gases do not form compounds with other atoms.