Covalent radius of atom

Z1 and Z2 denote the valencies of elements. AX denotes the difference of Basanov electronegativity of elements. Z/Rcov denotes of the ratio of valency to covalent radius of atom. 

The perturbed term r / Vof added in the one electron hamiltonian contracts the atomic orbitals (j>i, f) (the basis set), which results in an appropriate basis set to study molecules and periodic systems within the tight-binding approximation. The value of the confinement radius To is usually set between 1.85 r av and 2.00 ( "cov is the covalent radius of atom A). Eqn (12) is solved for the atoms A and B, separately. Then, it is possible to evaluate the integrals for A-A, A-B and B-B atomic pairs. Recently, Wahiduzzaman et have shown that the confinement radius could be tuned to reproduce the band electronic structure of many solids. 

Ghanty TK, Ghosh SK (1994) Simple density functional approach to polarizability, hardness, and covalent radius of atomic systems. J Phys Chem 98(37) 9197-9201... 

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... 

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. 

Each atom makes a characteristic contribution, called its covalent radius, to the length of a bond (Fig. 2.21). A bond length is approximately the sum of the covalent radii of the two atoms (36). The O—H bond length in ethanol, for example, is the sum of the covalent radii of H and O, 37 + 74 pm = 111 pm. We also see from Fig. 2.21 that the covalent radius of an atom taking part in a multiple bond is smaller than that for a single bond of the same atom. 

The covalent radius of an atom is the contribution it makes to the length of a covalent bond covalent radii are added together to estimate the lengths of bonds in molecules. 

The formation of dimeric products is unique for the case of boron, because analogous complexes with other elements are all monomeric [95]. This can be attributed to the small covalent radius of the boron atom and its tetrahedral geometry in four-coordinate boron complexes. Molecular modeling shows that bipyramidal-trigonal and octahedral coordination geometries are more favorable for the formation of monomeric complexes with these ligands. 

We conclude from these numerical examples that it is possible to give a quantitative and probably rather general expression of the Valley theorem (weak e dependence of the orbital in a finite volume around the nucleus) a variation of the energy of ca. 0.2 H results in a variation of thefunction / (r) smaller than 10% of the last extremum of ft r) until a distance of the nucleus equal to ca. 90% of the covalent radius of the corresponding atom. 

To accommodate this problem, scientists have come up with several approaches to measuring atomic sizes. A common one is called the covalent radius, which is half the distance between the nuclei of two identical atoms. This technique works well for atoms such as hydrogen or oxygen, both of which readily pair up to form and O2. But how would one determine the covalent radius of a noble gas, which exists only as single atoms ... 

The covalent radii for most of the elements were obtained by taking one-half of the length of a single bond between two identical atoms. For example, the covalent radius of sulfur is obtained from the length of the S—S bond in the S8 molecule ... 

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. 

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. 

According to Gordy (1946), electronegativity is represented by the value of the potential resulting from the effect of the nuclear charge of an unshielded atom on a valence electron located at a distance corresponding to the covalent radius of the atom. 

The now generally accepted scale of electronegativity was derived by Allred and Rochow and is known by their names. It is based on the concept that the electronegativity of an element is related to the force of attraction experienced by an electron at a distance from the nucleus equal to the covalent radius of the particular atom. 

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