I don't have a strong chemistry background, but I was thinking why do carbons have to make different kinds of orbital hybridization for double and triple bonds? Why doesn't a carbon make two sigma bonds into a double bond?
1$\begingroup$ It costs energy to hybridize and if you can make a stable bond without "paying" the cost the molecule would do that. The p Orbitals can bond through a pi bond without need for hybridization so the atom's orbitals just hybridize to sp2. en.m.wikipedia.org/wiki/Orbital_hybridisation the wiki really gives a good idea of how hybridization works. I hope i clarified some of the question. $\endgroup$– Avishai BarnoyJul 13, 2017 at 20:49
1$\begingroup$ Should always keep mindful that hybridisation isn't a real thing, just simply a concept to help understand bonding $\endgroup$– James DealonJul 13, 2017 at 22:19
Only one electron can be in an orbital at a time. There are three p orbitals, one in each of the x, y, and z axes. A pi bond is the overlap of one p oribital from each atom. Like the p orbital, a pi bond also can be rotated from the x axis to the y or z to produce a different unique pi bond. Because a sigma bond has rotational symmetry, rotating it does not give a unique bond. Therefore, you cannot have two of them between the same pair of atoms.
Edit: It appears this question has been asked before and there are much better answers than mine (Why can there not be more than one sigma bond in a set of bonds?)