And what I'll show next is a schematic that represents the relative

energies of the spdf electrons, and that's what we have here.

So as we look at the principle quantum number n which is labeled along the x axis

and the energy, we see that each one of these spd's and

f have different energy levels.

Now what we can do is we can come up with a scheme that will help us organize

the electrons as they fill across the periodic chart.

And we'll be looking then at the atomic numbers and the corresponding spd

electrons that are involved and the order in which these fill.

So if we use the device I have indicated on the right hand side

we have an arrow and so what that indicates is that the s electrons,

the one s electrons will be filled.

The first one is in the case of hydrogen where we have one electron.

The second is helium in which we have

the s in the first principle quantum number filled.

Then we go to the second level, the n equal two level.

And now what we have is a total of 2 electrons and

this time, it is the 1s and then the 2s, and

then the 2s will fill those and then we begin to fill the p.

In this case, we begin by looking at 2p, and

the p's have a total of 6 electrons in them.

The next, in terms of the level of filling will be the 3s electrons which again

have 2, if we continue on we'll have the 3p and the 4s.

Ultimately we'll begin with the 3d which represent what we will see in

a few minutes.

The d electrons and those electrons are associated with the transition metals,

and we'll see how they're grouped together.

And then again we as we continue to fill,

we'll start talking once again with p electrons.

And then ultimately, with the s electrons.

And we continue to do this, using the arrows and

following through as I have indicated at the bottom of the slide.

Now it turns out that there are some exceptions to this order of filling, and

we will wind up discussing those.

Now if we go back and consider a material like sodium, and

we look at the energy levels and the way these electrons wind up filling.

When we start out with the electrons in the 1s shell,

those inner electrons, and again they're two of them.

We go to the 2s, and now what we have is 2 electrons in that 2s shell.

We continue to fill and

then we completely wind up piling the p electrons with a total of 6.

Remember each one of those couples represent one electron with one spin and

the other the electron in the other spin.

Finally, we get to 3s which represents the top electron

that is in the sodium structure, and

we're going to ultimately refer to this electron as a valance electron.

Now when we talk about the electrons in the spd and

f series, what we're actually seeing are configurations that

are given by distribution functions where rather than seeing

a symmetrical cloud which is what we see in the s electrons.

But when we start looking at p electrons, d electrons and f electrons,

what we see is the fact that these electron orbits are highly directional.