Ionic Versus Covalent Bonding

In the introduction to this chapter, it was stated that ceramics, very broadly speaking, can be considered to be either ionically or covalently bonded. The next logical question that this chapter attempts to address is. What determines the nature of the bond  

Ionic compounds generally form between very active metallic elements and active nonmetals. For reasons that will become clear shortly, the requirements for an AB ionic bond to form are that A be able to lose electrons easily and B be able to accept electrons without too much energy input. This restricts ionic bonding to mostly metals from groups lA, IIA, and part of IIIA as well as some of the transition metals and the most active nonmetals of groups VlIA and VIA (see the periodic table). 

For covalent bonding to occur, however, ionic bonding must be unfavorable. This is tantamount to saying that the energies of the bonding electrons of A and B must be comparable because if the electron energy on one of the atoms is much lower than that on the other then electron transfer from one to the other would occur and ionic bonds would tend to form instead. 

These qualitative requirements for the formation of each type of bonding, while shedding some light on the problem, do not have much predictive capability as to the nature of the bond that will form. In an attempt to semiquantify the answer, Pauling established a scale of relative 

Pauling, The Nature of the Chemical Bond, 3rd ed., Cornell University Press, Ithaca, NY. 1960, 

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For a further discussion of ionic versus covalent bonding and the total bond energy resulting from the sum of the two, see Chapter 9, Electronegativity and Hardness and Softness."... 

There are few periodic generalizations that can be made concerning hypervalent molecules, since the factors contributing to stability, such as oxidation potential, central atom size, type of ligands, and ionic versus covalent bonding type, all interact in a complex manner. However, some general trends are evident. 

Thus, the bonding in metal compounds and complexes has traditionally been viewed as ionic, with a positive metal center interacting with negative ions, such as HO , 0 , Cl , AcO , and coordinate donor, Lewis acid-base interactions with a positive metal center interacting with negative ions and electron-pair Lewis bases, such as iNHs, iPPhs, HOH. Examples of ionic versus covalent bonding illustrate the tradition H+CH versus H-Cl (ls-3p), C +(C1 )4 versus C(-C1)4 [2sp -(3p)4], Fe +(C1 )3 versus Fe(-Cl)3 [3d sp2-(3p)3], H+-OH versus H-OH (ls-2p), C +(Q2-)2 versus 0=C=0 [2sp -(2p )2], and Fe +(0 ) versus Fe=0 [3d sp-(2p )]. Such ionic formulations for these molecules in an inert matrix are not consistent with their physical... 

K.M. Fromm (2002) Crystal Engineering Communications, vol. 4, p. 318 - An article that uses structural data to consider the question of ionic versus covalent bonding in group 2 metal iodide complexes. 

B, respectively, and partial negative charges of 0.4 to 0,5 for O. In the absence of any theoretical comparison these numbers cannot be directly translated into a comparison of ionic versus covalent bonding for B-O and Na-O, although the greater overlap density between B and O than between Na and O would indicate, as expected, a more covalent bond. 

Ionic versus Covalent Bonding ARIS, Animations... 

CIA Demonstration Conductivity Apparatus - Ionic Versus Covalent Bonds... 

D. Arvanitis, G. Comelli, T. Lederer, H. Rabus, K. Baberschke, Characterization of 2 different adsorption states for o on Cu(lOO)—ionic versus covalent bonding. Chem. Phys. Lett. 211(1), 53-59 (1993)... 

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