The Lanthanides and Actinides At this point, I'm going to show you an extended version of the periodic table applet--click here to open it. Instead of stopping after 36 elements, this one goes up to 103. Wow...there are a lot more transition metals underneath the first ten, plus more elements in the regular groups. What are those two separate rows at the bottom? And why is there an "f" column in the chart next to s, p, and d? f is the name of the next sublevel above d; primary level 4 is the first one to have an f sublevel. The old applet left off at the end of the fourth row of the periodic table, having just filled the 4p orbitals. The fifth row, as you can see for yourself, is pretty much a rerun of the fourth, filling 5s, 4d, and 5p. What about the sixth? Cesium (Cs) and barium (Ba) add the two 6s electrons...um, where do I go now? The element following barium is lanthanum (La), which begins the first of those separate rows you asked about. Based on what happened above, where would you expect the next electron to be added? In 5d--yup, there it is. But in the rest of that row, the electrons all go into the 4f sublevel. Hey, this is just like the transition metals--there's a whole collection of elements with the same valence electrons. Very good; these are also transition elements of a sort. It's as if they all belong in the sixth row, third column of the periodic table; that's why they're drawn separately. The elements in the row beginning with lanthanum are called the lanthanides, or rare earths. I bet the row underneath the lanthanides goes with the 5f sublevel. That's right; those are called the actinides, after actinium (Ac). The seventh row of the periodic table follows the same pattern as the sixth.

>