Chlorine covalent radius

A covalent radius is the radius of an atom that is bonded covalently to another. For example, one half the intemuclear distance in Cl, is the covalent radius of chlorine. A metallic radius is half the shortest intemuclear distance in a crystal of solid metal. 

In a molecule of chlorine, with the electronic structure Cl Cl , the covalent radius of chlorine may be described as representing roughly... 

The van der Waals radius is expected to be larger than the covalent radius, since it involves the interposition of two electron pairs between the atoms rather than one. Moreover, the van der Waals radius of chlorine should be about equal to its ionic radius, inasmuch as the bonded atom presents the same face to the outside world in directions... 

The single bond covalent radius of carbon may be taken to be about 0.77 A, just half of the C—C bond length in diamond. Similarly, the covalent radii of chlorine and iodine may be set at 0.99 A and 1.33 A, respectively, one half of the interatomic distances in the Ch and I2 molecules. 

Figure 1. A) A chlorine molecule, illustrating the difference between Van der Waals radius and covalent radius (from Pauling s book [2]).

Figure 8.8 Defining metallic and covalent radii. A, The metallic radius is one-half the distance between nuclei of adjacent atoms in a crystal of the element, as shown here for aluminum. B, The covalent radius is one-half the distance between bonded nuclei in a molecule of the element, as shown here for chlorine. In effect, it is one-half the bond length.

Figure 12.9 Covalent and van der Waals radii. As shown here for solid chlorine, the van der Waals (VDW) radius is one-half the distance between adjacent nonbonded atoms ( x VDW distance), and the covalent radius is one-half the distance between bonded atoms (5 x bond length).

Another radius that can be assigned to an atom is the covalent radius, which relates to the sizes of chemical bonds formed by the atom. For example, in the hydrogen molecule, H2, the atoms are 0.074 nm (0.74 A) apart each hydrogen atom is said to have a covalent radius of 7 x 0.074 = 0.037 nm. The van der Waals and covalent radii are shown in Figure 1.10 for the hydrogen and chlorine molecules. With the use of the two radii, the effective volumes of the molecules can be calculated easily. 

Now let us consider methyl chloride. The covalent radius of chlorine (Table 1.2) is about 0.22 A greater than that of carbon, so the C-Cl bond distance should be about 1.76 A Thus, we predict the molecular geometry of methyl chloride to be as shown in Figure 1.19(a). Spectroscopic data suggest, however, that the structure is like that shown in Figure 1.19(b). While the... 

The covalent radius of nonmetallic element is calculated according to the homonu-clear or heteronuclear nature of the molecules. Thus, in the case of homonuclear molecules (CI2, Br2, graphite) in solid state, this radius is equal to half the experimentally measured distance between the nuclei of two neighboring atoms. For heteronuclear molecules the distance between the two covalent bound atoms is experimentally determined. From that value, the value of the known radius is subtracted in order to obtain the unknown radius. For example, the length of the covalent Cl-Cl bond is 1.998 A, therefore the covalent radius of the chlorine atom is 0.994 A. If the covalent C-Cl bond is 1.766 A, the value of the known covalent radius of the chlorine atom is subtracted and so the covalent radius of C is obtained, that is 0.722 A. 

Radii measured for some elemeuts are used to determine the radii of other elements from distances between atoms in compounds. For instance, in a carbon-chlorine componnd, the distance between nuclei iu a C—Cl bond is 177 pm. Using the known covalent radins of Cl (1(X) pm), we find the covalent radius of C (177 pm 100 pm = 77 pm) (Figure 8.7C). 

The ionic radius of chlorine has the value 1.81 A (Chap. 13). The following distances between chlorine atoms of different molecules have been observed in the molecular crystal 1,2,3,4,5,(Whexachlorocyclo-hexane.-57 3,60, 3.77, 3.82 A these are close to twice the ionic radius. Similar agreement is shown by many other organic crystals and inorganic covalent crystals. Cadmium chloride, for example, consists of... 

Every covalent bond has its own characteristic length that leads to maximum stability and that is roughly predictable from a knowledge of atomic radii (Section 5.15). For example, because the atomic radius of hydrogen is 37 pm and the atomic radius of chlorine is 99 pm, the H-Cl bond length in a hydrogen chloride molecule is approximately 37 pm + 99 pm = 136 pm. (The actual value is 127 pm.)... 

Opposite to rebound reactions is the reaction Na + Ch — NaCl + Cl which proceeds via the spectator stripping mechanism. In this case, the crossing between the nonreactive covalent Na-Cl2 curve and the Na+Cl ion-pair curve, which promotes the reaction, occurs at a large distance [Re = 5.22 A, when using the chlorine adiabatic electron affinity in Magee s equation). This distance increases to 22.3 A when sodium is excited to the 3p P level. One would expect an increased reaction cross-section, but this is not observed because electron transfers at such large distance are inefficient. The overlap between the sodium HOMO and the CI2 LUMO is very small at these distances. As a result, when the crossing radius increases substantially, there is only a small effect on the dynamics of the reaction [164, 165]. 

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