What are Inner Transition Elements?
The elements constituting the f-block are those in which 4f and 5f orbitals are progressively filled. These elements are formal members of group 3 but are shown separately as f-block of the periodic table. The elements of f-block are also called inner transition elements.
The two series of inner transition elements that are 4f and 5f series are known as lanthanoids and actinoids respectively. The inner transition elements such as U, Th and Pa are providing good sources of nuclear energy.
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Main Characteristics of Inner Transition Elements
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- In the inner transition elements the third last shell is filled with electrons.
- The inner transition elements form coloured ions.
- The inner transition elements show variable valencies.
- Actinides are radioactive by nature.
- The inner transition elements beyond atomic number 92 up to 103 are synthetic as well as radioactive. They are not found in nature in the earth’s crust.
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General Electronic Configuration of Inner Transition Elements
The electronic configuration of the inner transition elements are 4f1-145d0-16s2 for the lanthanons beginning at cerium and ending at lutetium (Z = 71) and 5f1-146d0-17s2 for the actions beginning with thorium (Z = 90) and ending with lawrencium (Z = 103).
Because of the similar outer shell configurations, and energies of the f orbital electrons, the lanthanons as well as the actions are expressed to give state III without exceptions. All the elements in a series would have similar properties because of the same size and outer shell configuration, making their separation from one another tedious.
On account of similar outer shell electronic configuration and energies of f-orbital electrons, the lanthanides and actinides are expected to give oxidation state +3 without -exception. All the elements in a series have similar properties due to the same size and similar outer shell electronic configuration making their separation from each other rather difficult.
Inner Transition Elements in Periodic Table
The last electron in the configuration is added to (n-2)f orbitals. Lanthanides and actinides are f-block elements. All elements are metals. All elements of the actinide series are radioactive . Elements after U(92) are synthetic. However, to keep the symmetry of the table scientific the elements are placed at the bottom of the table.
When the elements are arranged according to Modern Periodic Law, a new table is obtained which is named as Modern Periodic Law, a new table is obtained which is named as Modern Periodic Table or Long form of Periodic Table. It differs in several respects from the Mendeleev’s periodic table. It can be described as follows.
Horizontal rows of elements are called periods and this periodic table contains seven periods.
There are eighteen vertical columns called groups. They are numbered as IA to VIIA and IB to VIIB making 14 columns, number VIII consists of three columns and the eighteenth column is numbered as 0. In the latest IUPAC system these groups are simply numbered as 1 to 18.
Lanthanoids and Actinoids
When differentiating electrons enters one of the 4f orbital, the element is said to belong to the first series of inner transition elements. Fourteen elements after lanthanum (La) belong to this series. These are called lanthanides or lanthanoids as they appear immediately after lanthanum in the periodic table. Though lanthanum does not possess any 4f electrons, it is usually included in lanthanide because lanthanum closely resembles lanthanoids.
The electron obtained on successive filling of 5f orbitals are called actinides or actinides. They are so called because they come immediately after actinium (Ac) in the periodic table. Fourteen elements from Th(90) to Lr(103) comprise actinide series, and are also called second inner transition series. Though actinium (Z=89) does not possess any 5f electrons, it is customary to study actinium with actinoids.
Difference between Lanthanoids and Actinoids
| S.No | Lanthanide | Actinoids |
| 1 | Last electron enters into a 4f orbital. | Last electron enters into a 5f orbital. |
| 2 | General electronic configuration 4f0-145d0-16s2 | General electronic configuration 5f1-146d0-17s2 |
| 3 | The decrease in atomic size is not regular as the decrease in size of tripositive ions (Ln3+) is regular. | There is a gradual decrease in the atomic and ionic (tripositive ion) size. |
| 4 | The principal and common oxidation state is +3. Some elements also show +2 and +4 oxidation states. | The common oxidation state is +3 but it is not always the stable state. The elements in the first half of the series frequently show higher oxidation states for example, the maximum oxidation state increases from +4 in Th to +5, +6 and +7 in Pa, U and Np respectively. |
| 5 | They do not form complexes readily. | They have much greater tendency to form complexes. |
| 6 | Their compounds are less basic. | Their compounds are more basic. |
| 7 | These elements are non-radioactive except promethium. | They are all radioactive. |
Frequently Asked Questions on Inner Transition Elements
What is another name for inner transition metals?
In the periodic table the lanthanides and actinides are groups of elements. They are the elements which are sometimes listed below the periodic table’s main section. The lanthanides and actinides contain thirty total elements. They’re also called the “core metals of transition.”
What is the difference between a transition metal and an F element?
The transition elements are in the d-block, and in the d-orbital have valence electrons. They can form several states of oxidation and contain different ions. Inner transition elements are in the f-block, and in the f-orbital have valence electrons. They are the Lanthanides, and the Actinides.
Why are transition metals different?
The transition elements are peculiar in that they may have an incomplete internal subshell that allows valence electrons in a shell other than the shell outside. Certain elements only have electrons of valence in their outer shell. It allows several oxidation states to form the transition metals.
Are inner transition metals reactive?
In the f-block are the inner transition metals, typically located at the bottom of the Periodic Table. These are almost as reactive as the alkali metals, and all actinides are toxic, and they have no commercial value. Nevertheless, the radioactive elements can be used as weapons or in nuclear power plants.
What do you mean by transition element?
The transition elements are those elements that at any rising oxidation state have a partially filled d or f subshell. Most generally the term “transition elements” refers to transition elements of the d-block.
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