Lanthanides are the rare earth elements of the modern periodic table, that is, the elements with atomic numbers ranging from 58 to 71 that are found after the element Lanthanum in the periodic table of elements. They are referred to as rare earth metals because the amount of these elements found in the Earth’s crust is extremely small (3 10-4 percent of the Earth’s crust). They are found in ‘monazitesand’ as lanthanide orthophosphates, which is a form of lanthanide. In the year 1925, the Norwegian mineralogist Victor Goldschmidt coined the term “lanthanide,” which means “lanthanide element.” The lanthanide family consists of fifteen metallic elements (ranging from lanthanum to lutetium), all of which are f-block elements with the exception of one: lutetium. The valence electrons of these elements are found in the 4f orbital of the atomic nucleus. Lanthanum, on the other hand, is a d-block element with an electronic configuration of [Xe]5d16s2 and is classified as such.

Lanthanide Compounds

Lanthanide Contraction is a term used to describe the process of converting lanthanide into lanthanide atoms. These elements, like most metals, have extremely high melting points (ranging from approximately 800 to 1600 degrees Celsius) and extremely high boiling points (ranging from approximately 800 to 1600 degrees Celsius) (ranging from roughly 1200 to 3500 degrees Celsius). All of the lanthanides are known to form Ln3+ cations, which are positively charged.

Elements in the Lanthanide Series

The elements of the Lanthanide series start from atomic number 57 and ends at atomic number 71. The Elements are as follows:

The Electronic Configuration of 

Lanthanum (La) Atomic number=57 is given by-  5d16s2

Cerium (Ce) Atomic number= 58 is given by- 4f15d16s2

Praseodymium (Pr) Atomic number=59 is given by- 4f36s2

Reactivity in the Chemical World

Physical Characteristics

1. Colored Ions are formed as a result of this process.
2. Lanthanides have a variety of applications.
3. Lanthanides are extremely dense metals with melting points that are even higher than those of the d-block elements. 
4. They combine with other metals to form alloys. 
5. These are the f block elements, which are also referred to as the inner transition metals because they are located within the f block. 
6. The electrons in the s, d, and f- orbitals of the inner transition elements/ions are possible.

Characteristics of the Lanthanide Series

If we include the lanthanides and actinides series in the periodic table for transition metals, the table will become excessively long and crowded. These two series are located at the bottom of the periodic table and are referred to as the 4f series (Lanthanide series) and the 5f series (Lanthanide series) (Actinides series). The 4f and 5f series are collectively referred to as inner transition elements.

In terms of their chemical and physical properties, all of the elements in the series are very similar to lanthanum and to one another as well. Some of the most important characteristics and properties are as follows:

1. They have a lustrous sheen to them and have a silvery appearance.
2. They are malleable metals that can even be cut with a sharp knife.
3. Depending on their basicity, the elements exhibit a variety of reaction tendencies. Some people are extremely reactive, whereas others take their time to react.
4. Because they are susceptible to corrosion and brittleness when exposed to other metals or non-metals, lanthanides should be handled with caution.
5. They all combine to form a trivalent compound in the majority of cases. They can also combine to form divalent or tetravalent compounds on occasion.
6. They have a magnetic pull.

Lanthanide Contraction

Lanthanide Contraction is a term used to describe the process of converting lanthanide into lanthanide atoms. When transitioning from La to Lu, the atomic size or ionic radius of tri positive lanthanide ions decreases steadily due to an increase in nuclear charge and electrons entering the inner (n-2) f orbital of the atom. Lanthanide contraction is the term used to describe the gradual decrease in size that occurs as the atomic number increases.

Consequences of Lanthanide Contraction 

The following points will provide a clear picture of the effect of lanthanide contraction:

• The size of an atom
• Difficulty in separating lanthanides from other elements
• The effect of hydroxides on the basic strength of water
• The formation of a complex system
• The ionisation energy of elements in the d-block

1. The size of an atom: The size of the atom in the third transition series is nearly the same as the size of the atom in the second transition series, which is a significant difference. For example, the radius of Zr equals the radius of Hf, and the radius of Nb equals the radius of Ta.
2. Difficulty in separating lanthanides from other elements: As a result of their similar chemical properties, the separation of lanthanides can be difficult due to the small difference in ionic radii between lanthanides and other elements. As a result, the separation of elements in their pure state becomes more difficult.

3. The effect of hydroxides on the basic strength of water: the effect on the basic strength of hydroxides decreases as the size of lanthanides decreases from La to Lu. As the covalent character of hydroxides increases, their basic strength decreases as well. La (OH)3 is therefore more basic, whereas Lu(OH)3 is the least basic compound.

4. Formation of complexes: Because of the smaller size but higher nuclear charge, there is a tendency to form coordinated structures. The concentration of complexes increases as the concentration of La3+ increases to Lu3+.Lanthanides with a 3+ oxidation state have a larger charge to radius ratio than those with a 2+ oxidation state. When compared to d-block elements, lanthanides have a lower ability to form complexes as a result. In spite of this, they form complexes with strong chelating agents such as EDTA, -diketones, oxime, and other similar compounds. They do not interact with one another to form P-complexes.

5. Ionization energy: Because the nuclear charge attracts electrons at a much higher rate than the other charges, the Ionization energy of 5d elements is much higher than that of 4d and 3d elements. All elements, with the exception of platinum and gold, have filled the s-shell in the 5d series.Elements ranging from hafnium to rhenium have the same Ionization Energy, and after Ionization Energy increases with the number of shared d-electrons, with Iridium and Gold having the highest Ionization Energy of any element.

Examples 

As the only metal that exists in a liquid state at room temperature, mercury is referred to as the “liquid metal.” Mercury’s  valence electrons are more tightly bound to the nucleus (lanthanide contraction), resulting in fewer s-electrons being involved in metallic bonding at the outer edges of the atom.

Lanthanide Electronic Configuration and Its Applications

Therefore, lanthanide elements and some of their compounds are used in nuclear control devices, shielding devices, and fluxing devices, among other applications. Lanthanides of the first f-block have a terminal electronic configuration of [Xe] 4f1-14 5d 0-16s2, and promethium (Pm) with atomic number 61 is the only synthetic radioactive element among the fourteen lanthanides. Promethium (Pm) is the only synthetic radioactive element among the fourteen lanthanides. Because the energies of electrons in the 4f and 5d orbitals are so close to one another, the 5d orbital remains vacant and the electrons enter the 4f orbital instead.