Hybrid Orbitals

[SunjinKim1A]

Can someone explain again how hybrid orbitals help determine the shape of the molecule?

[Joyce Xiong 4C]

Hey there!

Hybridization actually does not determine the shape of a molecule (the VSEPR does that), but what it does do, is it helps us explain how our bond order (number of bonds) and geometry is correct, although it doesn't seem correct when we look at the atomic orbitals of the central atom. To illustrate what I'm trying to say, lets look at the example of CH4

Carbon has 4 valence electrons, with the 2s orbital filled, leaving the 2p shell with 2 unpaired electrons. Without hybridization, you look at this model and think... how can Carbon form 4 bonds when only 2 electrons are avaliable for bonding? The answer is- you have to make 4 unpaired electron (rather than the 2 you have from carbon's atomic configuration), by "promoting" and electron up to the p orbital so that now you have 4 unpaired electrons (one is 2s, another in 2px, another in 2py, and another in 2pz). This process is called hybridization and it combines present atomic orbitals to form new orbitals, called hybrid orbitals. In the case of CH4, the resulting 4 orbitals become sp3 hybrids because there are one electron in the s orbital and 3 electrons in the p orbital (and most importantly, all 4 electrons are unpaired.) Each unpaired electron can now bond with the electron of the hydrogen atom, and the way the molecule bonds is explained.

As a side note, while you determine a hybridization scheme, it is important to make sure that the number of hybrid orbitals created matches the number of regions of electron density. There were 4 regions of electron density (4 single bonds) and thus there were 4 hybrid orbitals (1 s and 3 p).