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How can we qualitatively predict $\sigma-$bond strengths of overlap between:

  • $\ce{s-s}$
  • $\ce{s-p}$
  • $\ce{p-p}$
  • $\ce{sp-s}$
  • $\ce{sp-p}$
  • $\ce{sp-sp}$

etc.?

My school-book says $\ce{s-s}$ overlap bond strength is greater than $\ce{s-p}$ overlap which is greater than $\ce{p-p}$

Another book Inorganic Chemistry by JD Lee states this:

enter image description here

Are the facts stated in the above books correct or justified? Is there any order of orbital overlap strengths? If so can we predict it qualitatively?

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I think the issue might be what orbitals are being referred to. Both books could be correct if they are referring to different $\mathrm{p-p}$ overlap. For example, suppose two atoms are bonding along the z-axis. $\mathrm{p_z}-\mathrm{p_z}$ overlap would be greater than $\mathrm{s-s}$ because the lobes of the p orbitals extend out to meet each other between the two molecules. If however we looked at $\mathrm{p_x}-\mathrm{p_x}$ overlap, the $\mathrm{s-s}$ overlap would be greater because the p lobes don't extend toward each other. Increasing hybridization increases overlap because it combines the directionality of p orbitals (that they extend out away from the atom) and the electronic density of s orbitals (larger space for overlap to occur).

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  • $\begingroup$ The schoolbook asked about p orbitals on internuclear axis only! I feel schoolbook may be wrong because as you said p orbitals are more directional and should form stronger bonds.. $\endgroup$ – samjoe Aug 20 '17 at 2:44
  • $\begingroup$ @samjoe could you include the relevant passage from your textbook in your question? It might give more context to other people who might have some thoughts. $\endgroup$ – Tyberius Aug 20 '17 at 3:06
  • $\begingroup$ I am unable to provide with an image at the moment. Anyway my main objective here is to be able to easily predict bond strengths of overlap of orbitals! :) $\endgroup$ – samjoe Aug 20 '17 at 9:19
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    $\begingroup$ @samjoe Well then for now, I would say trust the Inorganic chemistry book and that hybridization increases overlap. I'm not certain what the other textbook is referring to. $\endgroup$ – Tyberius Aug 20 '17 at 17:03
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    $\begingroup$ @YUSUFHASAN so is your confusion why a hybridized orbital overlaps better than a pure p? It's really just a matter of hybridized orbitals having their density focused in one lobe, rather than equal lobes in the bonding and opposite direction. You could think of a chemical reaction changing the hybridization, but we can be more abstract and just think of the hybridization changing. Hybridization is just a mathematical construct and we can always choose an arbitrary mixing of the orbitals; We just happen to know that certain mixings due a better job at describing bonding. $\endgroup$ – Tyberius Oct 4 '18 at 4:02

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