Models Based On Spheres
Robert Hooke proposed a relationship between crystals and the packing of spheres. René Just Haüy argued that the structures of crystals involved regular lattices of repeating units with shapes similar to the macroscopic crystal. Barlow, who jointly developed the theories of space groups, proposed models of crystals based on sphere packings ( ca. 1890).
The binary compounds sodium chloride (NaCl) and caesium chloride (CsCl) have cubic structures but have different space groups. This can be rationalised in terms of close packing of spheres of different sizes. For example, NaCl can be described as close-packed chloride ions (in a face-centered cubic lattice) with sodium ions in the octahedral holes. After the development of X-ray crystallography as a tool for determining crystal structures, many laboratories built models based on spheres. With the development of plastic or polystyrene balls it is now easy to create such models.
Read more about this topic: Molecular Model
Famous quotes containing the words models, based and/or spheres:
“The greatest and truest models for all orators ... is Demosthenes. One who has not studied deeply and constantly all the great speeches of the great Athenian, is not prepared to speak in public. Only as the constant companion of Demosthenes, Burke, Fox, Canning and Webster, can we hope to become orators.”
—Woodrow Wilson (1856–1924)
“Whoever invented the meeting must have had Hollywood in mind. I think they should consider giving Oscars for meetings: Best Meeting of the Year, Best Supporting Meeting, Best Meeting Based on Material from Another Meeting.”
—William Goldman (b. 1931)
“Perhaps a modern society can remain stable only by eliminating adolescence, by giving its young, from the age of ten, the skills, responsibilities, and rewards of grownups, and opportunities for action in all spheres of life. Adolescence should be a time of useful action, while book learning and scholarship should be a preoccupation of adults.”
—Eric Hoffer (1902–1983)