Re: Which is the 1st Lanthanide--Lanthanum or Cerium?

Which is the 1st Lanthanide--Lanthanum or Cerium?

I am a HS chemistry teacher. when I first started teaching, the first Lanthanide was Lanthanum. Then Lanthanum was put into the transition block and the 14 Lanthanides are now seemingly considered to be Cerium through Lawrencium. (Actually, the last lanthanide is lutetium; lawrencium is one of the actinide series.)

But modern books still differ on this in how they show the Periodic Table. Some show La in the body of the chart in with the Transition metals (and Ce as the 1st Lanthanide) and others show La as the first member of the Lanthanide series with Lu in with the Transitions. I know that La is shown to have a d1 configuration with Ce configuration being d1 f1.But different books still show different placements. Has IUPAC ruled on which is considered to be the first Lanthanide, La or Ce? which do books seem not to agree? And if Cerium is the first Rare Earth then why not change the name of the series to the Ceride series instead of the Lanthanide Series?

A good case can be made (citation given at WebElements^TM) for placing Lu and Lr in the two slots below Sc and Y, based on ground-state electron configuration (f¹⁴, assigned by fitting the hydrogen-like-atomic-orbital model to spectroscopic results); but then, "there are no such things as orbitals" and assigning electrons to this or that subshell may well be an artifact of our model.

If you consult a book like Stwertka's Guide to the Elements ( here's my review of the first edition) you will notice that all the elements in the series lanthanum through lutetium (and, by extension, actinium through lawrencium) have properties similar to those of scandium and yttrium; they shade from somewhat more reactive at the end near barium to slightly less reactive at the end near hafnium.

The key point is that all the "lanthanide elements" belong in the slot below yttrium (and all the "actinide elements" in the next slot down, between radium and rutherfordium) by virtue of their chemical properties, which are largely governed by their more-or-less d¹ or d⁰ configuration in compounds.

Since lanthanum is the first of the series of elements fitting in the slot between barium and hafnium, and actinium is the first of the series of elements fitting in the slot between radium and rutherfordium, the series are correctly referred to as the lanthanide and actinide series, no matter how they are depicted on the periodic table.