Orbital hybridization and lone electrons

[CrimpJiggler]

Do single non bonding electrons (i.e. on a free radical) always occupy non hybrid orbitals? For example the methyl radical has trigonal planar molecular geometry so the lone electron must occupy a p orbital. Why doesn't it occupy an sp3 orbital instead?

 

[DrDu]

Think of it as a hole occupying a p orbital. A p orbital is higher in energy than an s orbital or a sp hybrid. So it is energetically advantageous for the hole being in a pure p orbital than in an sp hybrid.
Alternatively you can say that using sp2 for the bonds you maximize the occupancy of the low lying s orbital.

 

[CrimpJiggler]

A hole? I don't understand your explanation at all. By hole, do you mean a lack of energy? In other words, the electron has less energy than an electron pair and therefore occupies the p orbital to account for this lack of energy?

As for your 2nd explanation, wouldn't using sp3 maximize the occupancy for the s orbital regardless of whether one of the sp3 orbitals is only occupied by a lone electron? Inversely, you could say that sp2 hybridizing minimizes the occupancy of the p orbitals but it doesn't really because either way there are just as many electrons occupying the orbitals, regardless of how many of them are hybridized.

EDIT: Ah wait, I see what you mean now. By only putting pairs into hybrid orbitals then there are no vacant spaces left in the s orbital.