Covalent radii in A

Atom Radius Atom Radius Atom Radius 

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Figure 5.1 Van der Waals and covalent radii in a diatomic molecule.

Table 2 Atomic Orbital Covalent Radii in [A], see eq. (7.4) for the definition of the parameters Cq, ci and c2.

Use the covalent radii in Fig. 2.21 to calculate the bond lengths in the following molecules. Account for the trends in your calculated values, (a) CF4 (b) SiF4 (c) SnF4. 

Other Covalent Radii. In Cu20 and Ag20 each metal atom is equidistant from two nearest oxygen atoms, the interatomic distances corresponding to the radius values 1.18 and 1.39 A for Cu1 and Agl with coordination number two. In KAg(GN)2, in which each silver atom is similarly attached to two cyanide groups1), the effective radius of Agl is 1.36 A. It has been pointed out to us by Dr. Hoard that the work of Braekken2) indicates the presence of strings —Ag—G=N—Ag—G... 

The previous literature on the effects of partial covalence on interatomic distances is contradictory. Pauling (1960) cites the examples of CuF, BeO, AIN, and SiC where observed bond lengths are shorter than the sum of the covalent radii. He attributes these differences to partial ionic character and thus implies that partial ionic character shortens covalent bonds. This conclusion is in accord with the Schoemaker— Stevenson (1941) rule Dab = a + pb—C nx— b where > interatomic distance between A and B, rx and r = covalent radii of A and B, a and xb = electronegativity of A and B and C = constant. 

Assuming the covalent radii in the C—Cl bond are additive, what would be the Cl—Cl distance in each of the three dichlorobenzenes (Fig. 9-49) Assume that the ring is a regular hexagon and that each C—Cl bond lies on a line through the center of the hexagon. The distance between adjacent carbons is 140 pm. 

Comparison of our results with the correlation curve for OHO bridges shows that the [NHN]+ curve s maximum is shifted toward higher values of (5 and the isotope effect is somewhat higher. The difference between OHO and NHN in DMAN H+ cations, reflected in Fig. 19.4, may result from two effects. The first, discussed by Scheiner [10, 33], is due to different covalent radii and a slightly different charge distribution. The second effect should be ascribed to the diamagnetic field of the naphthalene 7t-electron system. 

Already the simple suggestion by Pauling[47] to estimate the bond length of a covalent bond in a molecule simply as the sum of the two covalent radii of the corresponding atoms... 

A metal ion encapsulated in the three-dimensional ligand cavity must be an acceptor bonded to the donor groups of all macrocycles forming the cage framework. This is time either when the metal ion size corresponds to the ligand cavity size or when the cavity can be transformed under the influence of the metal ion so that the distance between the central ion and the donor atoms of the cage is not over the sum of their ionic or covalent radii. In addition to the geometric parameters, the thermodynamic and kinetic stability of... 

Silver iodide is the only silver halide with an adamantine structure, the two elements having covalent radii in the ratio 1.34 1.33. Both AgCl (1.34 0.99) and AgBr (1.34 1.14) have a rock-salt structure and an ionic character. Gold (I) fluoride is unknown, and the chloride, bromide, iodide decrease in stability in that order, the formation of Aul being endothermic (d H, 5.52 kcal). With the exception of Aul, all are converted by water to the trihalide and metal, the chloride the most readily, possibly because the most soluble. 

Table 3. Atomic radii (in A) of the atoms which form B32 type compounds. rB32 is the half nearest neighbour distance in Zintl phases AB, r o , is the atomic radius according to Goldschmidt (C.N. 8), rjo is the ionic and r ov the covalent radius for tetrahedral coordination (C.N. 4) according to Pauling ...

Covalent radii are mostly used in organic chemistry. The simplest way to obtain a set of covalent radii is to half the distance between atoms linked by a covalent bond in a homonuclear molecule, such as H2. Covalent radii defined in this way frequently do not reproduce the interatomic distances in organic molecules very well, because these are influenced by double bonding and electronegativity differences between neighbouring atoms. In large molecules such as proteins, this has important structural consequences. 

The S—S distances collected in Fig. 1 and Table 1 should be compared with the corresponding sum of the Van-der-Waals radii [R(S- -S) =3.7 A] > on the one hand, and with the covalent radii in cyclic disulfides on the other. Typical values [f (S—S)] for the latter vary from 2.0 to 2.1 A This comparison reveals that the... 

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