So the lowest energy principal quantum number we know about is n =1.

If n = 1, then l = 0, and that's an s orbital.

And for an s orbital there's only one allowed value of m l and that's 0.

There's only one s orbital at each principal quantum number.

So there's a picture of my s orbital, and there's a spot when

I can put two electrons, remember I can draw two electrons in that box.

One of them would have a positive spin of one half, and

one of them would have a spin of negative one half.

So every time I draw a box I can put two electrons in the box.

I won't keep doing that, you just happen to note, you just need to remember that.

All right, now what if n = 2?

So that's the only orbital that's allowed for n = 1.

Only one orbital is allowed.

But what if n = 2?

Then what types of orbitals can we have?

If n = 2, I can have two different values for l.

l can be 0 or l can be 1.

If l = 0, that's an s orbital, and if l = 1, that's a p orbital.