Carbon covalent radius

The atomic radii Y, values are relative to a carbon covalent radius equal to 87.126 picometers (Yc = 1). Relative atomic electronegativities Xi and covalent radii Y/ were also used as atomic weights to account for heteroatoms in the definition of the Balaban modified distance connectivity indices, and J, respectively. 

Different ethylidyne species bond distances and angles (fQ = carbon covalent radius rj = bulk metal atomic radius)... 

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. 

Using the carbon atom covalent radius 0.77 A and the covalent radii given in Figure 19-3, predict the C—X bond length in each of the following molecules CF<, CBr4, CI4. Compare your calculated bond lengths with the experimental values C—F in CF4 = 1.32 A, C—Br in CBr = 1.94 A, C—I in CI4 = 2.15 A. 

In the course of the work it was found that the value assumed five years ago for the carbon double-bond covalent radius (obtained by linear interpolation between the single-bond and the triple-bond radius) is 0.02 A. too large in consequence of this we have been led to revise the double-bond radii of other atoms also. 

Graphite is perhaps the simplest layered structure. The intralayer C—C distance (142 pm) is twice the covalent radius of aromatic carbon (cf. 139 pm in benzene) and the Interlayer C—C distance is 335 pm, twice the van dcr Wools radius of carbon. The sheets are held together by weak van der Waals forces. Many substances can be... 

We should also mention the fact that an atomic radius is sensitive to the type of hybridisation of the atom s orbitals. It is well established that the covalent radius of a carbon atom increases with increasing p character in its hybrid orbitals, viz. sp < sp2 < sp3. 

Hightened reactivity of functional groups (e.g. Cl, Br, OH, OR, OCOR, NH2, SH) at the atoms of silicon, aluminum, titanium, phoshorus and other elements in comparison with their reactivity binded with oxygen. This is due to the fact that the silicon atom is one and a half times bigger than the carbon atom it has a covalent radius of 0.117 nm, whereas the radius of the carbon atom is only 0.077 nm. It follows that functional groups of the Si atom are much more distanced from each other than... 

This is explained by the fact that a silicon atom is much larger (the covalence radius of a Si atom is 0.117 nm) than a carbon atom (the covalence radius of a C atom is 0.077 nm) therefore, the distances between the hydroxyl groups at the silicon atom are rather large and impair intramolecular condensation (such a reaction requires a considerable deformation of valence angles). 

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. 

The decrease in bond lengths in (Ar—P=C=0)2 may be due to the reduced covalent radius of the sp2 ring carbon compared to the sp3-hybridized C atom. The dimerization of the phosphaketenes extensively corresponds to analogous reactions of ketoketenes (142, 142a). The small difference of energies between HOMO and LUMO molecular orbitals in the case of the unsubstituted phosphaketene explains the... 

The covalent radius of the silicon atom is one and one half that of the carbon atom thus rendering the silicon atom more sterically accessible. 

The molecular and crystal structure of (81) is simpler than that of ferrocene as only one polymorph featuring eclipsed conformation of the cyclopentadienyl rings, has been found at ambient and low (100 K) temperature. The larger metal-carbon distance (2.186 A in (81) vs. 2.03 or 2.06 A in ferrocene) corresponds to the larger metal covalent radius see Covalent Radii) and may also be responsible for the fact that an eclipsed conformation is found for the solid-state structure of decamethylruthenocene (82), as opposed to decamethylferrocene where more closely spaced methyl groups impose the staggered Dsd conformation. 

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