Why are the lanthanides and actinides separated on the periodic table?

The lanthanides are a group of elements originally discovered in rare minerals, hence their name “rare earths.” Since the elements were eventually found more widely than expected, they began to be called lanthanides. The lanthanides, along with the actinides, occupy two separate element rows of the periodic table. Both are groups of metallic elements.

Location of the lanthanides and actinides in the periodic table

In the periodic table there are two independent rows of elements, beginning respectively with the element whose atomic number is 57, which corresponds to lanthanum, and the element with atomic number 89, which corresponds to actinium. Although these two rows are placed separately on the periodic table, they actually correspond to a period in the middle of 6 and 7 respectively.

the block f

The first of the f subshells begin to fill at 4f, after level 6s, which implies that the f subshells are the two main energy levels behind. The general electronic configuration that exists in the elements of block f is (n -2) · f ^1-14 ns ² . The seven orbitals of the f subshell accommodate the 14 electrons, so that the f block accommodates 14 elements.

That is why the elements of the f block do not belong to a specific group, and are somehow “fitted” between groups 3 and 4. The lanthanides are the fourteen elements found from cerium (Ce), with atomic number 58 , up to lutetium (Lu), with atomic number 71. As a characteristic of the lanthanides, it stands out that they have a reactivity similar to that of group 2, which are the alkaline earth metals.

The actinides are the 14 elements that range from thorium (Th), with atomic number 90, to laurencium (Lr), with atomic number 103. The 5f sublevel is currently in the process of being filled by elements that are being discovered or synthesized. In addition, of all the elements that are part of the actinides, only four have been found naturally in nature, and all of them are radioactive elements.

Both the lanthanides and the actinides are sometimes referred to as “internal transition elements.”

Uses of lanthanides and actinides

Lanthanides have been widely used to increase the hardness and strength of metals. Among them, the use of cerium stands out, which is mixed with small amounts of lanthanum (La), neodymium (Nd) and praseodymium (Pr). These elements have been widely used in the oil industry to refine crude oil.

Erbium (Er) and other lanthanides are also used extensively for optical devices, such as night vision goggles and phosphorescent materials, among others. As for the actinides, they are a valuable primary source, since they are radioactive. These elements can be used as power sources for applications as varied as cardiac pacemakers and power generation for instruments that are even used on missions to the moon. On the other hand, uranium and plutonium have come to be used in nuclear weapons, as well as in nuclear power plants.

Sources

• 2.23: Lanthanides and Actinides. (2021). Retrieved 19 March 2021, from https://cutt.ly/vxuZE04
• Actinide – an overview | Science Direct Topics. (2021). Retrieved 19 March 2021, from https://www.sciencedirect.com/topics/materials-science/actinide
• Lanthanide Series – an overview | Science Direct Topics. (2021). Retrieved 19 March 2021, from https://www.sciencedirect.com/topics/materials-science/lanthanide-series