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.