The lanthanoids and actinoids, also known as the inner transition metals, are two series of elements that are placed at the bottom of the periodic table.
The lanthanoids, often referred to as the "rare earth elements," are located in period six (between barium and hafnium) and are composed of the elements with atomic numbers 57 (lanthanum) to 71 (lutetium). These elements are further classified as belonging to the f-block of the periodic table due to the filling of the 4f electron subshell. Lanthanoids are generally soft, malleable, and shiny metals, with high electrical and thermal conductivity. They tend to react slowly with water and oxygen but readily form compounds with other elements.
The actinoids, on the other hand, are placed in period seven (between radium and rutherfordium) and consist of the elements with atomic numbers 89 (actinium) to 103 (lawrencium). Similar to the lanthanoids, actinoids are also part of the f-block and are characterized by the filling of the 5f electron subshell. Actinoids are predominantly radioactive, with a few exceptions. They are highly electropositive and exhibit both metallic and nonmetallic behavior. Due to their radioactivity, they tend to undergo nuclear decay and can emit harmful radiation.
Both the lanthanoids and actinoids share certain common properties such as similar electron configurations, the presence of f electrons, and the ability to form stable coordination compounds. Additionally, they have a variety of applications, including catalysis, magnetic materials, nuclear energy, lasers, lighting, and electronics.