Nitrogen covalent radius

The strain energies of these five-membered heterocycles are relatively small with values of 23.5, 24.8 and S.SkJmoF estimated for tetrahydrofuran, pyrrolidine and tetrahy-drothiophene respectively (74PMH(6)199). The closeness of the values for the two former compounds reflects the almost identical covalent radii of oxygen (0.66 A) and nitrogen (0.70 A) atoms. The sulfur atom with a much larger covalent radius of 1.04 A causes a... 

Note that the N3- ion (radius 171 pm) is much larger than the nitrogen atom, for which the covalent radius is only 71 pm. The oxygen atom (radius 72 pm) is approximately half the size of the oxide ion... 

Boron, with a covalent radius of 0.85 A, is too small to coordinate to a porphyrin ligand through all four nitrogen atoms. There are two possible solutions to this problem, either to use a contracted porphyrin-type ligand or to coordinate more than one boron atom to a single porphyrin, and both of these have been realized. 

The variation can, however, be understood if it is assumed that repulsive interactions between the atoms or groups bonded to the nitrogen atom predominate over the valence-shell electron-pair repulsion. That repulsion between the substituents should dominate does not seem unreasonable, since the nitrogen atoms in these species are bonded to three or four atoms, all with a larger covalent radius than the nitrogen. 

The simplest diamine, hydrazine N2H4 (Table 3), is normally available as the monohydrate. An X-ray structure of the crystalline solid has been determined (there is some doubt as to the correct space group ) as well as an electron diffraction study of the vapor.The structxues of the di(hydrogen fluoride), di(hydrogen chloride) and monoperchlorate crown ether salts are also known. The N—N distance in hydrazine (1.499 A) is an important parameter, as one half this distance is used for the covalent radius of the single-bonded nitrogen atom. 

Fluorine has a very small van der Waals radius of 147 pm [6] and, although very difficult to measure, a covalent radius of approximately 60 pm [7-9]. Associated with that, it has the highest electronegativity in the whole periodic system of 3.98 on Pauling s scale [10], which inevitably causes every bond A-F to have considerably ionic character, unless A is oxygen, nitrogen, or fluorine itself [7]. The C-F bond is thus better described as C -F . ... 

Calculated from the metallic radius of 1.13 A for nickel. All covalent radii used in the table and elsewhere are from L. Pauling, TTie Nature of the Chemical Bond , Cornell, Ithaca, New York, 1960. Calculated from the octahedral nickelfn) radius of 1.39 A. The number of bonds averaged is given in square brackets. 0.03 A has been subtracted from the covalent radius of nitrogen to allow for sp hybridization. In five- and six-membered chelate rings. In four-membered rings the mean Ni-S distance is 2.21 A. See also Table 2. 

The average distance that a molecule travels between collisions is its mean free path. At room temperature and atmospheric pressure, the mean free path of a nitrogen molecule with a molecular diameter of 300 pm (four times the covalent radius) is 93 mn, or about 310 molecular diameters. If the nitrogen molecule were the size of a golf baU, it would travel about 40 ft between collisions. Mean free path increases with decreasing pressure. Under conditions of ultrahigh vacuum (10 ° torr), the mean free path of a nitrogen molecule is hundreds of kilometers. 

From an analysis of the (200) X-ray diffraction intensity (85), which reflects any differences in the number of electrons on the B and N atoms, and experimentally obtained electron density distributions (88) as well as theoretical analyses (90-96), cBN was found to have an electric polarity of B N" (5 0.4). Therefore, there is an electron charge transfer of about 0.4e from the B to the N atoms. As shown in Fig. 9, electrons forming covalent bonding shift toward the more electronegative N atoms. This shift of the bonding electrons is characteristic of III-V compound materials and provides properties different from those of diamond, which has a symmetric electron distribution with two electron density peaks. Cubic BN is usually considered to have both covalent (75%) and ionic (25%) aspects. The covalent radius of boron is said to be 20% larger than that of nitrogen in this connection. 

The values of f (l) given in the table for electronegative atoms are their normal covalent single-bond radii28 (except for boron, discussed below). The possibility that the radius 0.74 A. of Schomaker and Stevenson29 should be used for nitrogen in the metallic nitrides should be borne in mind. 

Revised Values of Double-Bond Covalent Radii.—This investigation has led to the value 1.34 A. for the carbon-carbon double-bond distance, 0.04 A. less than the value provided by the table of covalent radii.111 4 Five years ago, when this table was extended to multiple bonds, there were few reliable experimental data on which the selected values for double-bond and triple-bond radii could be based. The single-bond radii were obtained -from the study of a large number of interatomic distances found experimentally by crystal-structure and spectroscopic methods. The spectroscopic value of the triple-bond radius of nitrogen (in N2) was found to bear the ratio 0.79 to the single-bond radius, and this ratio was as-... 

Minimum non-covalent contacts for nitrogen and oxygen atoms are usually greater than the van der Waals radius... 

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