"And to go beyond that really requires some intensive quantum mechanics. So, we're going to stay with s and p-block. And we saw that if we had two atomic s-orbitals, when they blended to form the molecular orbital, it took on this sort of the ellipsoidal shape.

We called that a sigma orbital. And, the characteristic of the sigma orbital is that you have continuous electron density from one nucleus to the other. We said no holidays; constant electronic density.

We could then combine an s orbital and a p orbital, as for example in the case of hydrogen fluoride. In the case of s plus p, will end up with an orbital that looks something like this. And, it is also termed a sigma orbital because, again, if you look from one nucleus to the other, there is continuous electron density, no holidays...."