Difference Between Lanthanoids and Actinoids

Main Difference – Lanthanoids vs Actinoids

Lanthanoids and Actinoids are chemical elements that are present in lanthanide and actinide series of the periodic table respectively. These elements are known as f block elements. This is because their valence electrons are in the f orbital of their atoms. All Lanthanoids and Actinoids are metals. They are also called inner transition metals. This is because their outermost f orbitals are shielded by other orbitals. These elements are given names as such since the actinide series starts from a chemical called actinium and the lanthanide series starts from a chemical element called Lanthanum. The main difference between actinides and lanthanides is that actinides can form complexes easily whereas lanthanides do not form complexes easily.

Key Areas Covered

1. What are Lanthanoids
     – Definition, Chemical Reactions and Properties
2. What are Actinoids
     – Definition, Chemical Properties
3. What is the Difference Between Lanthanoids and Actinoids
     – Comparison of Key Differences

Key Terms: Actinoids, Actinium, F Block Elements, Inner Transition Metals, Lanthanides, Lanthanoids, Lanthanum

Difference Between Lanthanoids and Actinoids - Comparison Summary

What are Lanthanoids

Lanthanoids are chemical elements that can be found in the lanthanide series of the f block in the periodic table of elements. Lanthanoids are non-radioactive except for Promethium. Since atomic numbers of Lanthanoids range from 57 to 71, they are also composed of comparatively large atoms. The valence electrons of Lanthanoids are in the 4f orbital. They are also called Lanthanides.

Lanthanoids are metals and have a bright and silvery in appearance. They are very soft and can even be cut with a knife. The elements Lanthanum, cerium, praseodymium, neodymium, and europium of the lanthanide series are highly reactive compared to other members. When these metals are exposed to air, they form coatings of oxides. They get tarnished due to this reason.

Lanthanoids react rapidly with hot water but slowly with cold water. When these metals are contaminated with other metals such as calcium, they quickly corrode. But when Lanthanoids are contaminated with nonmetals such as nitrogen and oxygen, they become brittle. These contaminations alter the boiling point of the Lanthanoids.

Lanthanoids dissolve quickly in acids. They can react with oxygen and halides, but slowly. The most prominent oxidation state of Lanthanoids is +3. Other oxidation states that Lanthanoids show are +2 and +4. But they cannot have +6 oxidation state. Therefore, they cannot form complex molecules. Lanthanoids do not form oxocations such as oxides and hydroxides. The molecules formed by Lanthanoids are less basic.

Difference Between Lanthanoids and Actinoids

Figure 1: Lanthanide Nitrates

Almost all ions formed by Lanthanoids are colorless. Lanthanoids are electropositive elements. Therefore, they prefer to form molecules with electronegative elements. However, the changes in the chemical and physical properties are very less throughout the series.

What are Actinoids

Actinoids are chemical elements that can be found in the actinide series of the f block in the periodic table of elements. All Actinoids are radioactive elements due to their unstable nature. They have no stable isotopes. These elements are composed of very large atoms. Actinoids have their valence electrons in the 5f orbital. The actinide series is composed of chemical elements having the atomic numbers 89 to 103.

Actinoids are highly electropositive. This means they have a very little or no electron affinity. Since these are highly reactive elements, they ignite readily in air. Although they are metals, Actinoids are very soft. Some of them can even be cut with a knife. All the Actinoids are paramagnetic (can be attracted by an external magnetic field).

Main Difference - Lanthanoids vs Actinoids

Figure 2: Actinides

The most common and abundant Actinoids on earth are Uranium and Thorium. They are weakly radioactive and release high energy during radioactive decay. The prominent oxidation state among Actinoids is +3. In addition, Actinoids show oxidation states such as +4, +5 and +6.

Actinoids form basic oxides and hydroxides. They have the ability to form complexes with ligands such as chlorides, sulfates, etc. Most complexes of Actinoids are colorful. However, due to the radioactivity and heavy metal behavior, Actinoids are considered as toxic compounds.

Difference Between Lanthanoids and Actinoids

Definition

Lanthanoids: Lanthanoids are chemical elements that can be found in the lanthanide series of the f block in the periodic table of elements.

Actinoids: Actinoids are chemical elements that can be found in the actinide series of the f block in the periodic table of elements.

Series in the Periodic Table

Lanthanoids: Lanthanoids are in the lanthanide series.

Actinoids: Actinoids are in the actinide series.

Radioactivity

Lanthanoids: Lanthanoids are non-radioactive elements (except Promethium).

Actinoids: Actinoids are radioactive elements.

Valence Electrons

Lanthanoids: Lanthanoids have their valence electrons in a 4f orbital.

Actinoids: Actinoids have their valence electrons in a 5f orbital.

Oxidation States

Lanthanoids: Lanthanoids can have a maximum of +4 oxidation state.

Actinoids: Actinoids can have a maximum of +6 oxidation state.

Atomic Numbers

Lanthanoids: Lanthanoids include elements with atomic numbers ranging from 57 to 71.

Actinoids: Actinoids include elements with atomic numbers ranging from 89 to 103.

Conclusion

Lanthanoids and Actinoids are f block elements of the periodic table. They are metals but are very soft. They have different chemical properties. The main difference between actinides and lanthanides is that actinides can form complexes easily whereas lanthanides do not form complexes easily.

Reference:

1. Helmenstine, Anne Marie. “Get the Facts About the Actinides Element Group.” ThoughtCo, Available here.
2. “Lanthanides.” Science of Everyday Things, Encyclopedia.com, Available here.

Image Courtesy:

1. “Lanthanide nitrates” By Leiem – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Actinide-table” (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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