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:
“French rhetorical models are too narrow for the English tradition. Most pernicious of French imports is the notion that there is no person behind a text. Is there anything more affected, aggressive, and relentlessly concrete than a Parisan intellectual behind his/her turgid text? The Parisian is a provincial when he pretends to speak for the universe.”
—Camille Paglia (b. 1947)
“A two-parent family based on love and commitment can be a wonderful thing, but historically speaking the “two-parent paradigm” has left an extraordinary amount of room for economic inequality, violence and male dominance.”
—Stephanie Coontz (20th century)
“It launch’d forth filament, filament, filament, out of itself,
Ever unreeling them, ever tirelessly speeding them.
And you O my soul where you stand,
Surrounded, detached, in measureless oceans of space,
Ceaselessly musing, venturing, throwing, seeking the spheres to connect them,
Till the bridge you will need be form’d, till the ductile anchor hold,
Till the gossamer thread you fling catch somewhere, O, my soul.”
—Walt Whitman (1819–1892)