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We're told in chemistry class that the order of bond length is: triple < double < single

Can anyone explain WHY this is the case? Is it because multiple bonds involve stronger attraction between the two atoms or something else?

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    $\begingroup$ Yes, stronger attraction is quite enough of a reason. $\endgroup$ – Ivan Neretin Oct 17 '19 at 9:59
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    $\begingroup$ Do you know why the atomic distance is without any bond, i.e. the van der Waals distance, is larger than the atomic distance of covalently bonded atoms? This would be a starting point in discussing the more subtle question of single, double and triple bonds. There are two things that change when going from single to triple bond - the strength of the bond, but also the coordination geometry around the bonded atoms (for carbons, it has to be linear for triple bonds, whereas for a single bond, it could be tetrahedral). $\endgroup$ – Karsten Theis Oct 17 '19 at 14:30
  • $\begingroup$ Besides the screening effect you can also see that considering the orbital involved (s character). $\endgroup$ – Alchimista Oct 17 '19 at 18:24
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In general, in a single bond, there is involvement of sigma bonds only. In double bonds, there is also overlap between pi orbitals. More is the overlap shorter will be the distance between the atoms.

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    $\begingroup$ That's the start of an answer, but it still begs the question: why does more overlap imply shorter distance? $\endgroup$ – orthocresol Oct 17 '19 at 12:30

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