Physics 2000 Science Trek The Periodic Table

A Crash Course in Electron Configurations

As an example to illustrate how the chart works, click on element number 23, vanadium (V), in the periodic table. It has 23 protons and 23 electrons; the atomic number increases by one with each successive element.

I see the 23 electrons in the chart; they're in four different-colored rows, with three columns labeled s, p, and d.

Good. The higher up an electron is drawn on the chart, the more energy it has. In fact, the applet can tell you exactly how much energy you're dealing with: pick any electron and hold the mouse pointer over it.

If I do that, a little blue number pops up above the electron.

That number tells you, in eV, how much added energy it would take for that electron to escape from the nucleus. For the outermost electron in each atom, this value is called the ionization energy.

The colored rows represent the "main" divisions in energy; they're known as primary energy levels. You'll notice that vanadium has electrons in four different primary levels and is located in the fourth row of the periodic table; this is not a coincidence.

The colored rows aren't exactly straight; there's a little step up between the s column and the p column, and a bigger one between p and d.

That's right. s, p, and d are called sublevels; they're smaller "subdivisions" of energy within the primary levels. You refer to different energy levels using a number for the primary level plus a letter for the sublevel; for example, you might speak of an electron in a "3p" state or orbital. Each primary level has one more sublevel than the one below: the first primary level has only s orbitals, the second has s and p, the third s, p, and d, and so forth.

If you play around with the applet for a while, you'll discover that each sublevel has room for a certain number of electrons, and that they don't always get filled up in the order you might expect. If you'd like to know more about what's going on, read the heavy atoms discussion.


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