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Inner Transition Elements

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What are Inner Transition Elements?

Inner transition elements are the elements in which the last electron enters in the f-orbital. They generally belong to group 3 in the periodic table but are mentioned separately as the f block elements. These f block elements are known as inner transition elements.

There are two series of inner transition elements-

  • Lanthanoid series- If the last electron enters in 4f orbital, it is said to be the lanthanoid series.

  • Actinoid series- If the last electron enters in 5f orbital, it is said to be actinoid series.

In this article, we will study the main characteristics of inner transition elements. Also, the difference and similarities between lanthanoids and actinoids.


Main Characteristics of Inner Transition Elements

Lanthanoids: (Atomic number: 58 to 71)

  1. Atomic radii: There is a fairly decrease in the atomic radii of lanthanoids along with the series. This is due to the lanthanoid contraction. Lanthanoid contraction can be defined as the poor shielding effect of 4f orbital due to which positive nuclear charge has more effect on the outermost electron thus decreasing the atomic radii along with the series.

  2. Oxidation states: The most common oxidation followed by lanthanoids is +3. Sometimes also show +2 and +4 oxidation states. This variation is due to the extra stability of empty, partially filled, or fully filled f -orbital.

  3. They are generally metals and thus are good conductors of heat and electricity. The hardness of metals increases with an increase in atomic number.

  4. They form coloured ions due to the presence of electrons in f- orbital (narrow absorption bands).


Actinoids: (Atomic number: 90 to 103)

  1. Atomic radii: There is a fairly decrease in the atomic radii of actinoids along with the series. This is due to the actinoid contraction. Actinoid contraction can be defined as the poor shielding effect of 5f orbital due to which positive nuclear charge has more effect on the outermost electron thus decreasing the atomic radii along with the series.

  2. Oxidation state: The most common oxidation state shown by actinoids is +3(but not stable necessarily).

  3. Actinoids are highly reactive metals.

  4. Actinoids are mostly radioactive in nature.

  5. They are not naturally found in the earth’s crust, they are synthesized.


Electronic Configuration:

Lanthanoids: 4f1-145p65d0-16s2 {from cerium(Z=53) to Lutetium(Z=71)}

Actinoids: 5f1-146s26p66d0-17s2 {from thorium (Z = 90) to lawrencium (Z = 103)}.


Similarities Between Lanthanoids and Actinoids

The filling of the last electron to 4f orbital, the element said to belong to the first series of transition elements. 14 elements are there in the lanthanoid series after the lanthanum. As they occur immediately after lanthanum in the periodic table, these are called lanthanides or lanthanoids. Although lanthanum does not have any 4f electrons, since lanthanum closely resembles lanthanoids, it is commonly included in lanthanide. 


Actinides or actinides are the electrons obtained upon successive filling of 5f orbitals. They are named so because they appear in the periodic table immediately after actinium (Ac). Fourteen elements from Th(90) to Lw(103) form the sequence of actinides and are also known as the second series of inner transitions. Since actinium (Z=89) has no 5f electrons, the analysis of actinium with actinoids is customary.


Distinguish Between Lanthanoids and Actinoids

Some difference between lanthanoids and actinoids are listed below-


S.no

Lanthanoids 

Actinoids 

1.

The last electron of these elements enters in a 4f orbital.

The last electron of these elements enters in a 5f orbital.

2.

Elecctroic configuration:4f1-145p65d0-16s2 

Elecctroic configuration: 5f1-146s26p66d0-17s2 

3.

As the decrease in the size of tri-positive ions (Ln3+) is periodic, the decrease in atomic size is not regular.

In atomic and ionic (tri-positive ion) size, there is a gradual decrease.

4.

Their compounds are not very basic.

Their compounds are much more basic.

5.

Except for promethium, they are non-radioactive.

They are radioactive in nature.

6.

The principal and normal state of oxidation are +3. Some elements also exhibit oxidation states of +2 and +4.

The popular oxidation state is + 3, but the stable state is not always the same. For example, the elements in the first half of the sequence also display higher oxidation states, with the maximum oxidation state increasing from +4 in Th to +5, +6, and +7 in Pa, U, and Np, respectively.

7.

They do not form complexes readily.

They form complexes.


Applications of Inner Transition Elements:

  1. They are used in making nuclear weapons, for example, uranium. Uranium is highly reactive as its naturally occurring isotopes are unstable. Also, plutonium is widely used in making explosives.

  2. They are used in generating nuclear power plants.

  3. Lanthanoids are used to produce lasers.

  4. They are used in determining the age of the fossils and rocks. Widely used elements are Samarium and lutetium.

  5. Lathanoids are used to make strong magnets.

  6. They are widely used in making sunglasses.

  7. Medicinal uses: they are used in destroying the particular targeted cells in the body. Example cancerous cells.

  • Uranium is also used as a protective shield against radiations

  • They are also used as a tracker in the body.

Do You Know?

According to Lenntech, thorium is almost as plentiful as lead and at least three times as plentiful as uranium. According to Chemicool, the concentration of thorium in the Earth's crust is 6 parts per million by mass. Thorium is the 41st most common element in the Earth's crust, according to the Periodic Table.

FAQ (Frequently Asked Questions)

Question: Why are They Called Elements of Inner Transition?

Answer: They are named so because they appear in the periodic table immediately after actinium (Ac). Fourteen elements from Th(90) to Lw(103) form the sequence of actinides and are also known as the second series of inner transitions.

Question: What is the Difference Between the Elements of the Inner and Outer Transition?

Answer: The key distinction between transition metals and inner transition metals is that in the outermost d orbital, transition metal atoms have their valence electrons, while in the f orbital of the inner penultimate electron shell, inner transition metal atoms have their valence electrons.

Question:  Are Metals of Inner Transition Reactive?

Answer: The inner transition metals, usually found at the bottom of the Periodic Table, are in the f-block. These are almost as reactive as alkali metals, and all actinides are poisonous. Radioactive materials can nonetheless be used as weapons or in nuclear power plants.