Predicting sigma bond overlap strengths of s-s, p-p, s-p, sp-sp etc

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](https://i.stack.imgur.com/wSgxE.png)](https://i.stack.imgur.com/wSgxE.png)


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?




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).


 14

Although the general trend $\mathrm{s} < \mathrm{p} < \mathrm{sp}^n$ makes sense, these magic numbers $1.73$, $1.93$, $1.99$, and $2.00$ seem to have just been pulled out of a hat. If these are really "approximate strengths of bonds", a good book would justify these by showing *which* bonds they use to come up with these numbers.


Just to show one counterexample, it is commonly known that the strength of C–H bonds *increase* going from alkanes to alkenes to alkynes. That is to say, the bond strengths *increase* in the order $\ce{C\_{sp^3}-H} < \ce{C\_{sp^2}-H} < \ce{C\_{sp}-H}$. This clearly contradicts the supposed trend given in the book of $\mathrm{sp}$ orbitals forming slightly weaker bonds than $\mathrm{sp^3}$.


From the second table in [this Wikipedia section](https://en.wikipedia.org/wiki/Bond-dissociation_energy#Homolytic_versus_heterolytic_dissociation):





| Compound | Carbon hybridisation | C–H bond strength (kcal/mol) |
| --- | --- | --- |
| Ethane | sp3 | 101 |
| Ethylene | sp2 | 111 |
| Benzene | sp2 | 113 |
| Acetylene | sp | 133 |



As far as I am aware, this trend is mainly [rationalised using bond lengths](https://chemistry.stackexchange.com/q/32341/16683).



> 
> Are the facts stated in the above books correct or justified?
> 
> 
> 


Some parts of it (e.g. the general trend of $\mathrm{s} < \mathrm{p} < \mathrm{sp}^n$) might be correct, as already well addressed by Tyberius' answer, but other parts (especially these magic numbers) are highly debatable.


 4