„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. They are also called inner transition metals. This is because their outermost f orbitals are shielded by other orbitals. 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.

 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. 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. Lanthanides include: lanthanum (La)*, cerium (Ce)*, praseodymium (Pr)*, neodymium (Nd)*, samarium (Sm)*, europium (Eu)*, gadolinium (Gd)*, terbium (Tb)*, dysprosium (Dy)*, holmium (Ho)*, erbium (Er)*, thulium (Tm)*, ytterbium (Yb)*, lutetium (Lu)*. The rare earth elements (REEs) are comprised of the lanthanide elements plus scandium and yttrium, which have similar physical properties and are often found in the same ores and deposits.

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). 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”. The Actinoid group includes the following elements: Actinium (Ac),Thorium (Th), Protactinium (Pa), Uranium (U), Neptunium (Np), Plutonium (Pu), Americium (Am), Curium (Cm), Berkelium (Bk), Californium (Cf), Einsteinium (Es), Fermium (Fm), Mendelevium (Md), Nobelium (No), Lawrencium (Lr).

* on the 2017 CRMs (27) list

References:

Pediaa, Available from: http://pediaa.com/difference-between-lanthanoids-and-actinoids/ Accessed: 21.06.2018

 CRMs (27) (2017) COMMUNICATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT, THE COUNCIL, THE EUROPEAN ECONOMIC AND SOCIAL COMMITTEE AND THE COMMITTEE OF THE REGIONS on the 2017 list of Critical Raw Materials for the EU