Interatomic distance, covalent bonds

Values found for interatomic distances and bond angles in the thirteen hydrocarbons studied are given in Table XIV. The carbon-carbon singlebond distance is found to have the constant value 1.54 = = 0.02 A., being unaffected by the presence of an adjacent double bond or benzene nucleus (provided that it does not form part of a conjugated system). The carbon-carbon double-bond distance in allene and acetylene has the value 1.34 A. This is 0.04 A. less than that formerly given by the table of covalent radii, which has accordingly been revised. The effect of the revision on the bond distance-resonance curve is discussed. 

In Chapter 8, we emphasize the loss and gain of. electrons, leading to the formation of electrically charged ions, such as Na+ and Wien eTecfons are shared, a molecule is formed, and the atoms are connected by a covalent bond. In this chapter we emphasize the approximate shapes, interatomic distances, and bond energies of molecules and molecular ions that are held together by covalent bonds. 

The distance between the nuclei of two atoms forming a covalent bond is called the bond length. Interatomic distances and bond lengths... 

This table gives information on the geometric structure of selected molecules in the gas phase, including the overall geometry, interatomic distances, and bond angles. The molecules have been chosen to provide data on a wide variety of chemical bonds and to illustrate the influence of molecular environment on bond distances and angles. The table is restricted to molecules with conventional covalent or ionic bonds, but it should be pointed out that structure data on many loosely bonded complexes of the van der Waals type have recently become available. The references below contain data on many molecules that are not included here and give additional information such as uncertainties and isotopic variations. 

Interatomic distances between a given pair of elements can vary substantially, from covalent bond lengths and dative (or donor-acceptor) bond lengths to secondary bond interatomic distances. Bond lengths vary to some extent with the coordination number of the central atom, and there is no clear-cut distinction between these three types of bond. Thus, for tin-oxygen bonds, there is a broad range of observed interatomic distances. Covalent Sn-0 bonds are shortest in four-... 

As in the case of ions we can assign values to covalent bond lengths and covalent bond radii. Interatomic distances can be measured by, for example. X-ray and electron diffraction methods. By halving the interatomic distances obtained for diatomic elements, covalent bond radii can be obtained. Other covalent bond radii can be determined by measurements of bond lengths in other covalently bonded compounds. By this method, tables of multiple as well as single covalent bond radii can be determined. A number of single covalent bond radii in nm are at the top of the next page. 

The single-bond covalent radius of C can be taken as half the interatomic distance in diamond, i.e. r(C) = 77.2pm. The corresponding values for doubly-bonded and triply-bonded carbon atoms are usually taken to be 66.7 and 60.3 pm respectively though variations occur, depending on details of the bonding and the nature of the attached atom (see also p. 292). Despite these smaller perturbations the underlying trend is clear the covalent radius of the carbon atom becomes smaller the lower the coordination number and the higher the formal bond order. 

Relationships between covalency, interatomic distances and magnetic properties in halides and chal-cogenides. R. D. Shannon and H. Vincent, Struct. Bonding (Berlin), 1974,19,1-43 (50). 

Covalent Radii of Atoms and Interatomic Distances in Crystals containing Electron-Pair Bonds. 

We have constructed a number of sets of atomic radii for use in compounds containing covalent bonds. These radii have been obtained from the study of observed interatomic distances. They are not necessarily applicable only to crystals containing pure covalent bonds (it is indeed probable that very few crystals of this type exist) but also to crystals and molecules in which the bonds approach the covalent type more closely than the ionic or metallic type. The crystals considered to belong to this class are tetrahedral crystals, pyrite and marcasite-type crystals, and others which have been found on application of the various criteria discussed in the preceding section to contain covalent bonds or bonds which approach this extreme. 

In other crystals an octahedral metal atom is attached to six non-metal atoms, each of which forms one, two, or three, rather than four, bonds with other atoms. The interatomic distance in such a crystal should be equal to the sum of the octahedral radius of the metal atom and the normal-valence radius (Table VI) of the non-metal atom. This is found to be true for many crystals with the potassium chlorostannate (H 61) and cadmium iodide (C 6) structures (Table XIB). Data are included in Table XIC for crystals in which a tetrahedral atom is bonded to a non-metal atom with two or three covalent bonds. The values of dcalc are obtained by adding the tetrahedral radius for the former to the normal-valence radius for the latter atom. 

In the preceding sections it has been shown that in a large number of crystals containing covalent bonds, cited as examples, the number and distribution of the bonds are in good agreement with a classification deduced from quantum mechanical considerations, and, moreover, there exist regularities in the observed interatomic distances which may be expressed by assigning covalent radii to the atoms, dependent in a... 

A number of questions related to those taken up in this paper, such as the distances between atoms not directly connected by bonds, the use of interatomic distances as a criterion for distinguishing between ionic and covalent bonds, etc., have been discussed in a paper by Huggins2). 

In the discussion of metallic radii we may make a choice between two immediate alternative procedures. The first, which I shall adopt, is to consider the dependence of the radius on the type of the bond, defined as the number (which may be fractional) of shared electron pairs involved (corresponding to the single, double, and triple bonds in ordinary covalent molecules and crystals), and then to consider separately the effect of resonance in stabilizing the crystal and decreasing the interatomic distance. This procedure is similar to that which we have used in the discussion of interatomic distances in resonating molecules.7 The alternative procedure would be to assign to each bond a number, the bond order, to represent the strength of the bond with inclusion of the resonance effect as well as of the bond type.8... 

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