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Inner Transition Elements-Definition, General Characteristics, Lanthanoids, Characteristics of Lanthanoids, The Actinoids, Characteristics of Actinoids, Practice Problems, FAQs

Inner Transition Elements-Definition, General Characteristics, Lanthanoids, Characteristics of Lanthanoids, The Actinoids, Characteristics of Actinoids, Practice Problems, FAQs

Have you heard about nuclear weapons in news? In your history book, you must have studied the nuclear bomb attack on Hiroshima and Nagasaki during world war II. The United States of America dropped an atomic bomb on Hiroshima and Nagasaki, Japan. The city was utterly destroyed when the nuclear bomb exploded above it.

Has this ever come to your mind, what type of chemicals do nuclear weapons consist of? 

The answer is Plutonium, a highly reactive element, was used to make the nuclear bombs that were dropped on Hiroshima and Nagasaki. Because these elements are dangerous, governments regulate their manufacture and use.

Let's know more about elements like Plutonium, these elements are called inner transition elements.

While reading history, you must be surprised how one can remember the old dates. Whenever you went to a museum you must have seen things around thousand of years ago. Do you find these interesting?

Events, discoveries, and innovations are a part of human history. To make it easier to remember, we label events with the dates they occurred and how is possible for historians to find dates related to pasts. Inner transition metals are used by scientists and archaeologists to assess the age of fossils and other materials such as rocks. 

Let’s begin with the study of some interesting facts about inner transition metals. These metals are remarkable because they were among the latest to be identified in the periodic table.


Table of content:

  • What are inner transition metals?
  • General characteristics of inner transition metals
  • The Lantanoids
  • General Characteristics of Lanthanoids
  • The Actinoids
  • Characteristics of Actinoids
  • Practice Problems
  • Frequently asked questions-FAQ

What are inner transition metals?

Inner transition elements are those in which an additional electron enters the (n-2)f orbitals. The electrical configuration of these elements' valence shells is (n-2)f1-14(n-1)f0-1ns2 Because the extra electrons travel to f-orbitals in the (n-2)th main shell, these are known as 

f-block elements.

Lanthanides, or rare-earth, are elements in the 4f-block. 5f-block elements are also known as actinides or actinones. Because of their strong resemblance to Lanthanum and Actinium, the names Lanthanides and Actinides were given. The first inner transition series is lanthanides, while the second inner transition series is actinides.

The lanthanides and actinides are frequently represented as a distinct tiny "island" beneath the main body of the periodic table in order to condense it.


General Characteristics of inner transition metals:

  • The third last shell of the inner transition elements is filled with electrons.
  • The inner transition elements form coloured ions.
  • Variable valencies are shown by the inner transition elements.
  • Actinides are naturally radioactive.
  • Beyond atomic number 92, the inner transition elements are both synthetic and radioactive. They aren't found in the earth's crust in nature.

The Lanthanoids:

From lanthanum to lutetium, the lanthanide series of chemical elements consist of fifteen metallic chemical elements with atomic numbers 57 to 71. The rare earth elements are made up of these fifteen lanthanide elements, as well as the chemically related elements scandium and yttrium.

It should be noted that the atoms of these elements have a common electrical structure of 6s2 but varied occupancy of the 4f level. All tri positive ions (the most stable oxidation state of all lanthanoids) have electronic structures of the form 4fn (n = 1 to 14 with increasing atomic number).

Let us cover some important trends in the periodic table:

  • Electronic configuration: 

For lanthanoids starting with cerium and finishing with lutetium

(Z = 71), the electronic configuration of the inner transition elements is 4f1-145d0-16s2.

  • Atomic size and Ionic size: 
  • The additional electron reaches the 4f-subshell in lanthanides but not the valence-shell or sixth shell. 
    • Because the shape of the f-sub shell is very diffused, there is no similar rise in the mutual shielding effect of 4f-electrons, the shielding effect of one electron in the same sub-shell by another in the same sub-shell is very modest, even smaller than that of d-electrons. 
    • The outermost shell electrons in the nucleus suffer greater nuclear attraction as a result of this. As a result, as we progress from La (57) to Lu (71), the atomic and ionic radii continue to decrease. 
    • Below is the graph which is showing the atomic radii of Lanthanoids

  • The lanthanoid contraction (a decrease in atomic and ionic radii from lanthanum to lutetium) is a distinctive aspect of the lanthanoids' chemistry. 
  • It has far-reaching implications in the chemistry of the elements' third transition series. The drop in atomic radii (derived from metal structures) is not as consistent as it is in M+3 ions. 
  • Of course, this contraction is comparable to that seen in a regular transition series and is due to the same cause i.e; improper shielding of one electron by another in the same sub-shell. With the increase in nuclear charge down the series, however, the shielding of one 4f electron by another is smaller than that of one d electron by another. With rising atomic number, the diameters shrink in a pretty regular pattern. 
  • The radii of the members of the third transition series are remarkably similar to those of the corresponding members of the second series due to the cumulative effect of the lanthanoid series contraction, known as lanthanoid contraction. 
  • The nearly identical radii of Zr (160 pm) and Hf (159 pm), which result from the lanthanoid contraction, account for their coexistence in nature and the difficulties in separating them.

  • Oxidation state: 
  • The +II and +III chemicals are the most common lanthanoids. However, +2 and +4 ions are occasionally found in solution or in solid compounds. 
  • The increased stability of empty, half-filled, or filled f subshells causes this irregularity in ionisation enthalpies. The noble gas structure favours the creation of CeIV, although it is a strong oxidant that reverts to the common +3 state. Ce+4/ Ce+3 has an E value of + 1.74 V, indicating that it may oxidise water. However, because the reaction rate is slow, Ce(IV) is an excellent analytical reagent.
  • Pr, Nd, Tb, and Dy have a +4 state as well, but only in oxides, MO2. Eu+2 is created by losing two s electrons, and its f7 configuration is responsible for its production. Yb+2, which has the f14 configuration, is also a reductant. Tb+4 is an oxidant with half-filled f-orbitals. Samarium behaves similarly to europium in that it has both +2 and +3 oxidation states.

General Characteristics of Lanthanoids:

  • Lanthanoids are silvery-white soft metals that tarnish quickly when exposed to air.
  • With rising atomic numbers, the hardness of metal rises with samarium being steel hard metal.
  • They have a conventional metallic structure and are good heat and electricity conductors.
  • Except for Eu and Yb, and infrequently Sm and Tm, density and other characteristics shift smoothly.
  • In the solid-state and in aqueous solutions, many trivalent lanthanoid ions are coloured. The existence of f electrons accounts for the colour of these ions.
  • Neither the La+3 nor the Lu+3 ion exhibit any colour because of empty f-orbitals and fully filled f-orbitals respectively.
  • Because of the excitation within the f level, the absorption bands are narrow.
  • Other than the f0 type (La+3 and Ce+4) and the f14 type (Yb+2 and Lu+3), all lanthanoid ions are paramagnetic.
  • In terms of chemical behaviour, the series' initial members are extremely reactive, almost similar to calcium, but as the atomic number increases, they behave more like aluminium. E values for the half-reaction, except for Eu, which has a value of –2.0 V, Efor the half-reaction is in the range of –2.2 to –2.4 V. The general half cell reaction is:
  • When metals are heated with carbon, carbides such as Ln3C, Ln2C3, and LnC2 are produced.
  • They burn halogens to produce halides (LnX3) .
  • On reacting with dilute acids, they liberate hydrogen gas.
  • Lanthanides when burned in presence of air(O2) forms lanthanide oxides(Ln2O3).

The Actinoids:

Actinides or actinides are electrons obtained by successively filling 5f orbitals. They acquire their name from the fact that they are the next element in the periodic table after actinium (Ac). The actinide series, which includes 14 elements ranging from Th(90) to Lw(103), is also known as the second inner transition series. Despite the fact that actinium (Z=89) has no 5f electrons, it is common to analyse actinium using actinoids.

Let us cover some important trends of the periodic table:

  • Electronic configuration: The electrical configuration of 7s2 is thought to be shared by all actinoids, with varied occupancy of the 5f and 6d subshells. The fourteen electrons are formally added to 5f, though not in thorium (Z = 90) but from Pa onwards the 5f orbitals are completed at element 103. The stabilities of the f0, f7, and f14 occupancies of the 5f orbitals are related to the abnormalities in the electronic configurations of actinoids, as they were also in lanthanoids. Am and Cm configuration are [Rn]5f77s2and [Rn]5f76d17s2 respectively. Although the 5f orbitals are similar to the 4f orbitals in terms of their angular component of the wave function, they are not as buried, and so 5f electrons can engage in bonding to a far higher amount.
  • Atomic size and Ionic size: The actinoids follow the same general tendency as the lanthanoids.

Throughout the sequence, the size of atoms or M3+ ions decreases gradually. This is known as actinoid contraction (similar to lanthanoid contraction). However, due to poor shielding by 5f electrons, the shrinkage is larger from element to element in this series.

  • Oxidation states of Actinoids: There is a wider variety of oxidation states, which is due to the fact that the 5f, 6d, and 7s levels have similar energies. The actinoids have a +3 oxidation state in general. In the early part of the series, the elements usually have higher oxidation states. For example, the maximal oxidation state of Th increases from +4 to +5 , +6 , and +7 in Pa, , and Np, respectively, but declines in subsequent elements.

General Characteristics of Actinoids:

  • The actinoid metals all have a silvery appearance but differ in structure.
  • Metallic radii have significantly more irregularities than lanthanoids, which gives rise to structural variety.
  • Actinoids, especially when finely separated, are highly reactive metals.
  • When boiling water is applied to them, for example, a mixture of oxide and hydride is formed.
  • The majority of non-metals combine with them at moderate temperatures.

Related link: https://www.youtube.com/watch?v=EAQGKdam8sE

Practice Problems:

Q1. The electronic configuration of cerium in +3 oxidation state is

a. [Xe]4f15d16s2
b. [Rn]4f25d06s2
c. [Xe]4f15d06s0
d. [Rn]4f15d26s1

Answer: C
The electronic configuration of cerium is [Xe]4f15d16s2 . Cerium in +3 oxidation state looses +3 electrons and thus gets a configuration of [Xe]4f15d06s0.

Q2. In flashlight powder alloy of ___________ is used.

a. Cerium-calcium
b. Cerium-magnesium
c. Samarium-magnesium
d. Samarium-calcium

Answer: B
Flashlight powders contain cerium-magnesium alloys.

Q3. ___________salts are used in glass industries for imparting colours

a. Uranium
b. Plutonium
c. Americium
d. Californium

Answer: A
Uranium salts are used in the glass industry (to impart a green colour), the textile business, the ceramic industry, and medicines.

Q4. In both solid and aqueous solutions, ions with 2 to 6 electrons in 5f-orbitals are coloured because of

a. charge transfer spectra
b. transition of d-d electrons
c. ligand to charge transfer spectra
d. transition of f-f electrons

Answer: D
In both solid and aqueous solutions, ions with 2 to 6 electrons in 5f-orbitals are coloured. The f-f transition is responsible for the colour.

Frequently asked questions-FAQ

Q1. Can we use inner transition metals in electric appliances?
Yes, we can use inner transition metals for coating in electronic equipment. This is one of the most profitable uses of inner transition metals. The element thorium is beneficial for coating tungsten wire.

Q2. Can inner transition elements be used for medical purposes?
These metals are utilised for medical purposes in addition to powering nuclear power reactors. Uranium, for example, is employed as a barrier against radiation.

Q3. How many electrons are there in the uranium element?
In a neutral Uranium atom, there are 92 electrons present in it.

Q4. Can we create alloys from inner transition metals?
Yes, we create alloys from inner transition metals. Inner transitional metals combine multiple metals with magnetic characteristics to generate a durable permanent alloy.

Related topics


Potassium Permanganate

lanthanide contraction

important compounds of silver


Important compounds of Copper

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