Ionic-covalent resonance

[aamera]

Today my colleague at college want my help about valence & molecular orbital theory.There was a sentences in a book which I could not explain well.that was" Molecular orbital theory based upon delocalizations while valence bond theory based upon ionic_covalent resonance ,when electron moves from less electronegative atom to more electronegative atom" Please help me ,what is ionic_covalent resonance?

[woelen]

I do not know the term, but I think it describes the fact that in most real chemical compounds the bonds are not purely ionic, nor purely covalent. Many many compounds have inbetween bonds.

 

Purely ionic compounds have separate ions in a crystal lattice, with totally separated charges. Examples are NaCl and CsF, they consist of Na(+) ions and Cl(-) ions, or Cs(+) ions and F(-) ions.

 

Purely covalent compouds are CH4 and CO2.

 

There are, however many inbetween compounds. A compound like CuCl2 is often called a salt, consisting of Cu(2+) ions and Cl(-) ions, but in reality it better can be described as a structure with Cu(2d+) and Cl(d-) charge, with d being a number between 0 and 1. The Cu-atoms are loosely bonded to the Cl-atoms, making it somewhat covalent, and at the same time, charge is separated, negative charge being withdrawn towards the chlorine atoms, but it is not fully withdrawn. So, CuCl2 can best be regarded as an intermediate compound, with covalent properties, and somewhat ionic properties. Many salts are of this type, espcially the metal halides, but also acetates and in general salts of weak acids.

[aamera]

I do not know the term, but I think it describes the fact that in most real chemical compounds the bonds are not purely ionic, nor purely covalent. Many many compounds have inbetween bonds.

 

Purely ionic compounds have separate ions in a crystal lattice, with totally separated charges. Examples are NaCl and CsF, they consist of Na(+) ions and Cl(-) ions, or Cs(+) ions and F(-) ions.

 

Purely covalent compouds are CH4 and CO2.

 

There are, however many inbetween compounds. A compound like CuCl2 is often called a salt, consisting of Cu(2+) ions and Cl(-) ions, but in reality it better can be described as a structure with Cu(2d+) and Cl(d-) charge, with d being a number between 0 and 1. The Cu-atoms are loosely bonded to the Cl-atoms, making it somewhat covalent, and at the same time, charge is separated, negative charge being withdrawn towards the chlorine atoms, but it is not fully withdrawn. So, CuCl2 can best be regarded as an intermediate compound, with covalent properties, and somewhat ionic properties. Many salts are of this type, espcially the metal halides, but also acetates and in general salts of weak acids.

No I don't think so. You know valence bond theory deals with covalent bonding.Ionic character is just due to unequal sharing coz of different electronegativity. Although I don't know the answer but still i can't digest your explanation too.

[jowrose]

Yeah, I'm learning about both of these theories in a chemistry class right now and am a little confused, particularly by the molecular theory. The whole bonding and antibonding, sigma, pi, sigma-star, all that stuff can be a little intimidating. Well, to me at least...