Why are double bonds shorter than single bonds? We're told in chemistry class that the order of bond length is:
triple &lt; double &lt; single

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