Lanthanides and Actinides — Overview & Properties

Lanthanides and Actinides of the Periodic Table

Lanthanides and Actinides make up two different groups on the periodic table. They are typically displayed below the main table area in two rows. The lanthanides consist of elements 57-71 and the actinides consist of elements 89-103. They have many of the same properties as other metals and are found in various colored compounds like the transition metals.

Lanthanides and Properties

Lanthanides have similar properties that other metals do. They are silvery in appearance but are soft enough that they can be cut. Most are very reactive, especially with some nonmetals like oxygen and the halogens. So, they must be stored in oil. This is similar to alkali and alkaline earth metals.

Lanthanides are also known as rare earth elements. Some are more common that other elements, but they are difficult to isolate. Most are naturally occurring whereas many actinides are made synthetically.

Actinides and Properties

Actinides share similar characteristics with lanthanides. They are silvery, have harder densities, and are reactive. What sets them apart is that only four actinides are found naturally. The others are made in a laboratory! All actinides are radioactive meaning that they are unstable and lose energy. Thorium, plutonium, and uranium are commonly found in nuclear reactors and other nuclear devices.

(Video) Where is the F-block?

by Daniel Price

In this video, Dr. Daniel Price introduces the f-block elements. He starts by looking at the modern periodic table. Often, we have the f-block thrown to the bottom. But why? And how does their chemistry relate to the other elements? As we move across a period, we know the atomic number increase. As we move down a group, the elements have the same number of valence electrons. So, they experience similar chemical reactions. But, the f-block gets tricky. These questions are the same problem that plagued Mendeleev's periodic table. He didn't know where to put d-orbitals elements. We don't know where to put the f-block!

Why is the f-block so tricky? Dr. Price considers the elements leading to the lanthanides. Cesium and barium behave like alkali and alkaline-earth metals. Based on the atomic number, lanthanum should come next. What's the problem? Let's skip over group three. The problem is that the next element that acts like group 4 is hafnium. Its atomic number is 72! So, we have 15 elements that should go in group 3! Dr. Price confirms this by examining the electron configurations of two sets of elements. First, he examines lanthanum and actinium. They would make sense. Based on atomic number, they are the following elements. Next, he looks at lutetium and lawrencium. They could make sense two since their atomic number precedes group 4. What's the result? Both sets of elements could be in group 3! Which option is correct?

How can we solve the problem? Maybe we can use the chemical properties. Next, Dr. Price examines the atomic radius, electronegativity trend, and melting point. It seems like lutetium should be the next d-block element. But, that raises another problem. Lanthanum would be the first f-block element. So, what? It doesn't have any orbital electrons in the f orbitals! What can we do?! Dr. Price urges us to rethink our periodic table.

If you want to understand why the f-block is unique, this video is for you! It's a great introduction and displays excellent scientific reasoning.