Why was the F block of the periodic table created?

I am confident others with expertise in this area will provide specific scientific reasons, but arguably the underlying one is the same that accounts for all science - Curiosity.

 

My research is on Lanthanides and to very slightly correct Borek's statement, Promethium (Pm), the 5th element in the lanthanide series, is naturally unavailable. It can only be artificially synthesized and is radioactive.

By the way, look up to the ceiling in some building. If you see a fluorescent lamp or LED lamp, the chance is, there are f-block elements in it. Specifically, Ce, Eu, and Tb for fluorescent lamps, and Ce for LED lamps. (Just to note that these days, there are increasingly more "warm" fluorescent lamps and LED lamps, which the composing elements are different.) If you have a cellphone or iphone or whatever phone with a camera, there's a little yellowish device next to it that you can use it for flashlight. Most likely, it is made out of Ce:YAG on a blue emitting diode.

If I recall correctly, smoke detectors contain Americium (I forgot the specific isotope), a crucial element for the device to work. There are also depleted Uranium ammunition and armor plates. Neodymium is commonly used in lasers and magnets. Gadolinium compounds are used as an imaging agent for MRIs.

Basically, they are used everywhere.

 

The first non-natural actinide elements where synthesized in the Manhattan atomic bomb project. Namely Plutonium was used in the "Fat man" bomb droped on Nagasaki.

 

And because these minerals contained rather low content of lanthanide ions and was also difficult to separate each other due to similar chemical properties, they were named "rare-earth" (lanthanides + scandium and yttrium). This is a very misleading name because rare-earth elements are rather plentiful in Earth's crust.


Fun fact: "Rare-earths" in Japanese is "希土類 (kidorui)", however it used to be written "稀土類 (also read kidorui)". The first letter of the latter form literally only means "rare". However, it was changed later into the first letter of the former form, which can mean "rare", "hope", or "noble". I am speculating that this is because they realized the importance of these elements after their properties were studied.

(Note to moderators: I believe using foreign language was appropriate in this case.)

 

Further to the etymological point. At the time the term 'rare earth' was coined, 'earth' was sometimes used as a synonym for an oxide, which was the form in which most (well, some... i think the historical issue may be a bit muddled, or maybe it is just my recollection that is) rare earths (at the time) were found. Just one of those quirky linguistic things.

diogenesNY