--%>
Assignment Help - homework help

What is covalent radii? Explain its calculation.

Average covalent radii can be assigned on the basis of molecular structures.


The accumulation of structural data by spectroscopic studies and both electron and x-ray diffraction studies allows one to investigate the possibility fo assigning a covalent bound molecule, i.e. of assigning a covalent radius to each atom. One begins by assigning half the length of a homonuclear bond as the covalent radius of the atoms forming the bond. Thus, from the equilibrium bond length of Cl2 of 199 pm, one obtains the value of 100 pm for the covalent radius of chlorine. From the carbon-carbon distance of 154 pm in ethane, for example, one obtains a value of 77 pm for the covalent radius of carbon and so forth. To proceed, one must now establish the extent to which the length of covalent bonds can be treated in terms of the sums of such covalent radii. 

More extensive treatments of this type show that the bond lengths of many bonds are given within a few picometers by the sum of assigned atomic covalent radii. This suggests that covalent bonds have lengths sufficiently independent of factors other than the fixed radii for there to be some value in assigning radii to the bonded nuclei. 

Some tests of additivity of covalent bond radii, pm:

390_covalent radii.png 

Further comparisons of these values with experimental results indicate, as shown in fact by some of the examples of table 1, that serious discrepancies can occur between simply predicted covalent-bond lengths and those observed. The C-F bond, for example, is calculated from the data of table 1 to have a length of 146 pm, whereas microwave spectral results forCH3F give it as 138.5 pm and electron-diffraction results for CF4 give 132 pm.

Such discrepancies led V. Schomaker and D. P. Stevenson to suggest that a bond length calculated from covalent radii must be adjusted for the difference in electronegativity of the bonded atoms. They suggested the relation:

rAB = rA + rB - 90 (xA - xB) r in pm

Some but not all, the interesting violations of simple covalent radii additivity are removed by this empirical expression. In other cases the Stevenson-Schomaker correction makes the agreement with the observed length pooper than that obtained by a simple addition of the covalent radii. Although a number of factors must be operating to affect the length of a bond between a pair of nuclei in any given molecule, the covalent radii of table 2 are often of value in estimating this bond length.

Covalent radii for atoms involved in single-bonded compounds, pm:

   Related Questions in Chemistry

  • Q : Strength of Nacl in solution To 5.85gm

    To 5.85gm of Nacl one kg of water is added to prepare of solution. What is the strength of Nacl in this solution (mol. wt. of nacl = 58.5)? (a) 0.1 Normal (b) 0.1 Molal (c) 0.1 Molar (d) 0.1 FormalAnswer:

    		•
  • Q : Explanation of oxygen family. Group 16

    Group 16 of periodic

    		•
  • Q : How haloalkanes are prepared from

    Alkyl halides can be prepared from alkanes through substitution and from alkenes through addition of halogen acids or through allylic substitution.    From alkanesWhen alkanes are treated with halogens, chlo

    		•
  • Q : Explain Photoelectron Spectroscopy. The

    The energies of both the outer and inner orbitals of atoms and molecules can be determined by photoelectron spectroscopy.Energy changes of the outermost or highest energy electron of molecules were dealt with here in a different passion. The energies of ot

    		•
  • Q : Simulate the column in HYSYS The

    The objective of this work is to separate a binary mixture and to cool down the bottom product for storage. (Check table below to see which mixture you are asked to study). 100 kmol of feed containing 10 mol percent of the lighter component enters a continuous distillation column at the m

    		•
  • Q : Vapour pressure related question Help

    Help me to solve this question. Which of the following is incorrect: (a) Relative lowering of vapour pressure is independent (b)The vapour pressure is a colligative property (c)Vapour pressure of a solution is lower than the vapour pressure of the solvent (d)The

    		•
  • Q : Molecular basis of third law. The

    The molecular, or statistical, basis of the third law can be seen by investigating S = k in W.The molecular deductions of the preceding sections have led to the same conclusions as that stated in the third law of thermodynamics, namely, that a value can be

    		•
  • Q : Hybridization Atomic orbitals can be

    Atomic orbitals can be combined, in a process called hybridization, to describe the bonding in polyatomic molecules. Descriptions of the bonding in CH4 can be used to illustrate the valence bond procedure. We must arrive a

    		•
  • Q : Explain the polymers and its types.

    Polymers are the chief products of modern chemical industry which form the backbone of present society. Daily life without the discovery and varied applications of polymers would not have been easier and colourful. The materials made of polymers find multifarious uses and applications in all walk

    		•
  • Q : What is covalent radii? Explain its

    Average covalent radii can be assigned on the basis of molecular structures. The accumulation of structural data by spectroscopic studies and both electron and x-ray diffraction studies allows one to investigate the possibili

    		•