Question

What is the term for the two series of elements that include Ce-Lu and Th-Lr?

Short answer

They are called Lanthanides and Actinides.

Step-by-step solution

Identify the Series

The elements Ce-Lu and Th-Lr belong to two specific series on the periodic table known as the Lanthanide series and the Actinide series, respectively. We can identify them based on their atomic numbers and positions in the periodic table.

Define the Lanthanide Series

The Lanthanide series includes elements from Cerium (Ce, atomic number 58) to Lutetium (Lu, atomic number 71). These elements are f-block elements, positioned in the 4f sublevel of the periodic table.

Define the Actinide Series

The Actinide series contains elements from Thorium (Th, atomic number 90) to Lawrencium (Lr, atomic number 103). Like the Lanthanides, these elements are f-block elements, located in the 5f sublevel of the periodic table.

Conclusion

Thus, the elements Ce-Lu are part of the Lanthanide series, and the elements Th-Lr constitute the Actinide series, which collectively are referred to as 'Inner Transition Metals.'

Key concepts

Periodic Table

The Periodic Table is a systematic way of organizing the chemical elements. It is arranged in order of increasing atomic number, which is the number of protons in the nucleus of an atom. Each row in the table is known as a period, while each column is known as a group. This layout helps to highlight periodic trends, such as elements with similar electron configurations appearing at regular intervals.
In the context of the f-block and inner transition metals, it is important to understand why these elements are set apart from the main body of the periodic table. They slot in between the s-block on the left and d-block on the right, forming a special group of elements.

f-block Elements

F-block elements are a group of elements in the periodic table that are characterized by filling their f-orbitals. These elements include the Lanthanides and Actinides, which are known for their unique electronic configurations. Unlike other elements, f-block elements do not always follow expected electron configurations precisely, leading to unique chemical behavior. They generally have large atomic and ionic sizes, and possess high oxidation states. Their chemistry is influenced by this peculiar arrangement of electrons.
The lanthanides, from cerium (Ce) to lutetium (Lu), fill the 4f orbitals, while the actinides, from thorium (Th) to lawrencium (Lr), fill the 5f orbitals. These elements are important in various high-tech applications, such as superconductors and nuclear technology, thanks to their unique properties.

Inner Transition Metals

The term 'Inner Transition Metals' encompasses the Lanthanides and Actinides. These metals sit below the main body of the periodic table, which explains why they are often called "inner" transition metals. This group's distinguishing feature is the filling of the f-orbitals. Since f-orbitals can hold up to 14 electrons, both the Lanthanide and Actinide series have 14 elements each. What makes them transitional is that they exhibit properties of both transition metals (d-block) and other metals, hence their strategic placement in the periodic table.
Their unique atomic structure contributes to diverse uses. Lanthanides are used in the creation of powerful permanent magnets, phosphors for color television tubes, and catalysts in petroleum refining. Meanwhile, actinides, with their ability to release substantial energy during radioactive decay, are crucial in nuclear energy and medical diagnostics.