Why Are Lanthanides and Actinides Separated on the Periodic Table?

[wScott]

Why are there two rows separate from the general table at the bottom of the diagram? We just started chemistry this week and I'm interested in it, I might try to get it into an online course next year if at all possible, so I just felt like asking a question.

 

[Janus]

The vertical columns of the periodic table are arranged to contain elements that have simular chemical and physical properties.

The two rows at the bottom(called the Lanthanide and Actinide series) are elements that would all fit into group IIIB, in periods(horizontal rows) 6 and 7. since there is only one spot on the chart for all the elements in each series, they are listed separately at the bottom of the table.

 

[Markjdb]

The Lanthanides (topmost row) are often called the rare Earth metals, as they are usually only found in very small quantities in the Earth's crust. Most of them have some industrial application. Most of the Actinides are synthetically prepared and thus decay quickly, the notable exception being of course uranium.

 

[wScott]

What does synthetically prepared mean?

 

[chroot]

"Synthetically prepared" means created by man in a laboratory with a particle accelerator. Such elements don't occur in nature.

- Warren

 

[z-component]

Synthetic elements are those not found in nature, but instead are created in labs. Actinides decay quickly because they're unstable with the number of neutrons and protons in a particular element's atom, and eventually diminish. Some have very short lives before they decay.

EDIT: Warren beat me.

 

[wScott]

Thanks for the info you guys.

 

[Astronuc]

The separation of lanthanides and actinides from the periodic table is arbitrary - lack of space on most papers.

There are graphical images that put the lanthanides and actinides (the so-called f-block) in the same table, much like the transitional metal (d-block) are placed between the s-block elements (alkali and alkaline earth) and p-block elements (mostly non-metals, halogens, and noble gases).

Alternative periodic tables can be found at - http://chemlab.pc.maricopa.edu/PERIODIC/styles.html