Single bonds covalent

QTAIM provides a definitive answer to the question of whether two atoms are bonded or not even in ambiguous cases [87, 88] and, as a consequence, the molecular graph, i.e., the chemical structure, is readily defined by this theory. Two atoms are bonded if their nuclei are linked in space by a line of maximal electron density termed the bond path [89, 90] (see Fig. 1). A single bond path links the nuclei of chemically bonded atoms irrespective of the mode of the bonding covalent (single or multiple), hydrogen, van der Waals, ionic, metallic, etc. The properties of the eleetron density determined at the point of lowest density along the bond path, where... 

Moving now to nitrogen we see that it has four covalent bonds (two single bonds + one double bond) and so its electron count is 5(8) = 4 A neutral nitrogen has five electrons m its valence shell The electron count for nitrogen m nitric acid is one less than that of a neutral nitrogen atom so its formal charge is +1... 

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. 

FIGURE 2.21 Cov.ilent radii ot hydrogen and the p-block elements (in picometers). Where more than one value is given, the values refer to single, double, and triple bonds. Covalent radii tend to become smaller toward fluorine. A bond length is approximately the sum of the covalent radii of the two participating atoms. 

It is customary to use the line between two atomic symbols, A—B, to represent a normal covalent bond, with the usual amount of ionic character. In the discussion that follows, A B is used to represent a pure covalent single bond, and A+B to represent the ionic structure that is hybridized with A B to give A—B. A pure covalent double bond is represented by A=B. Thus in the molecule NF3 we might describe each NF bond as involving N+ F , N F , and N F +, that is, as having some covalent double-bond character. 

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. 

The measured 5 values and estimated intensities, averaged for sixteen photographs, given in Table I lead to the radial distribution curve shown in Fig. 1, with principal peaks at 1.22, 2.34, and 3.33 A. These correspond closely with C-N = 1.47 A. (the sum of the single-bond covalent radii), N-N = 1.24 and 1.10 A., and the C-N-N angle = 120°, the peak at 1.22 A. representing the... 

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. 

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-... 

TABLE 7.3 Topical Energies for Some Covalent Single Bonds (see Table 1.7) and the Corresponding Approximate Wavelengths... 

Identify the bonds as single covalent bonds or double covalent bonds. 

In a covalent single bond between unlike atoms, the electron pair forming the a bond is never shared absolutely equally between the two atoms it tends to be attracted a little more towards the more electronegative atom of the two. Thus in an alkyl chloride (20), the... 

The unstable organic molecules have fixed structures because of the nature of their bonds. The structure of methane is a tetrahedron of covalent single —C — H bonds. Where the structure of even a simple compound is based on double bonds, such as in an ethylene, there are two forms labelled trans and cis geometric isomers ... 

From elemental sulfur to selenium and tellurium, intermolecular interactions (,secondary bonds, soft-soft interactions) play an increasing role. According to N. W. Alcock,1 the term secondary bond describes interatomic distances longer than covalent single bonds but shorter than van der Waals interatomic distances.1 In many cases secondary bonds can also be described as coordinative Lewis base - Lewis acid or charge transfer (donor-acceptor) types of interactions. 

The indicated bond in butane is a nonpolar covalent single bond between two carbon atoms. 

A halogen molecule contains one nonpolar covalent single bond, as shown by its Lewis structure. As we descend the 7A family from F2 to I2, the size of a halogen atom increases and so the bond length increases. The strength of the X-X bond varies it increases from F2 to Cl2, then decreases from Cl2 to Br2 to I2. 

Bonding < Metallic > Covalent Covalent Single atoms... 

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