Coordination Number


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coordination number

[kō‚ȯrd·ən′ā·shən ‚nəm·bər]
(physics)
The number of nearest neighbors of a point in a space lattice, of an atom or an ion in a solid, or of an anion or cation in a solution.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Coordination Number

 

in crystallography, the number of identical neighboring atoms or ions closest to a given atom or ion in a crystal. Straight lines connecting the centers of nearest atoms or ions in a crystal form the coordination polyhedron, with the given atom in its center.

Different polyhedrons may correspond to the same coordination number. The coordination number in the structures of diamond, silicon, germanium, and sphalerite is 4, and the coordination polyhedron is a tetrahedron. Each sodium ion in sodium chloride, NaCl, is surrounded by six chlorine ions, and each chlorine ion is surrounded by six sodium ions, meaning that the coordination numbers are 6 for both types of ions and the corresponding polyhedron is an octahedron. The coordination number of calcium ions in fluorite, CaF2, is 8 and the corresponding polyhedron is a cube, whereas the coordination number for F ions is 4 and the coordination polyhedron is a tetrahedron. The highest possible coordination number is 12, which is typical of metals with cubic or hexagonal close-packed structure. Metals with a body-centered lattice have a coordination number of 8. Semiconductor crystals, which do not have close packing of atoms, have coordination numbers of 4 or 6.

In chemistry, the coordination number is the number of atoms or atomic groups directly bonded to a given atom in complex compounds. The concept of coordination numbers is also used in descriptions of fluids and amorphous bodies. In this case, the coordination number is the average number of the nearest neighbors of the atom; it may be fractional. The coordination number is a measure of short-range order in liquids and amorphous bodies.

M. P. SHASKOL’SKAIA

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The great advance of the RMC method is that the coordination number, [CN.sub.ij], can be obtained from the final particle configurations.
The Effect of the Average Coordination Number. Figures 9(a)-9(c) show the curves of the average coordination number in the sample during the loading process when the strain is less than 1%.
The analysis of the intensity of the absorption bands at 30,000, 35,500, and 12,700 [cm.sup.-1] in the UV-Vis-DRS of all the samples showed that as the number of [Ti.sup.3+] cations with coordination numbers less than 6 increased, the number of oxygen defects ([O.sub.2.sup.-]) in the titanium dioxide structure decreased.
In the bulk water (Figure 4(a)), the coordination number of H shows systematic changes as a function of solution density.
It is established that in case of complex Cd(II) tetrafluoroborates with organic ligands with average values [pK.sub.a] the binds with coordination number of Cd equal to four of general formula [Cd[L.sub.4]][(B[F.sub.4]).sub.2] in case of monodentate and [Cd[L.sub.2]][(B[F.sub.4]).sub.2] in case of bidentate organic ligands are implemented.
In the whole MD simulation process, the total innermost shell coordination numbers of [Fe.sup.2+] with its surrounding is 6.006 which approximate its coordination number of [Fe.sup.2+] in its bulk solution.
In developing a simple method to characterize the bimetallic interactions, the correlation between the ratio of Pt-Ru to Pt-Pt characteristic peak intensity ([I.sub.Pt-Ru]/[I.sub.Pt-Pt]) and the ratio of Pt-Ru to Pt-Pt coordination number ([N.sub.Pt-Ru]/[N.sub.Pt-Pt]) estimated from detailed EXAFS analysis was employed.
The glass transition reflects a change in the coordination number of the network forming atoms and destruction of the network structure brought about by the formation of some nonbridging atoms.
In our simulation, one region of the specimen underneath the indenter is selected to calculate the coordination number (CN) and hydrostatic pressure during loading and unloading of the indenter and the size is 50 [Angstrom] x 50 [Angstrom] x 25 [Angstrom].
The first is a regular octagon (8R), with all its atoms having coordination number 3; the second is either a pair of pentagons or a nonregular octagon with two dangling bonds, denoted as 8N.
2-4 were the lattice coordination number, z, and the excess transition isobaric specific heat, [DELTA][C.sub.PP].

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