Compare the chemistry of actinoids with that of the lanthanoids with special reference to:
(i) electronic configuration (iii) oxidation state
(ii) atomic and ionic sizes and (iv) chemical reactivity.
(i) electronic configuration (iii) oxidation state
(ii) atomic and ionic sizes and (iv) chemical reactivity.
Solution and Explanation
(i) Electronic configuration
The general electronic configuration for lanthanoids is [Xe]54 4f0-14 5d0-1 6s2 and that for actinoids is [Rn]86 5f1-14 6d0-1 7s2 . Unlike 4f orbitals, 5f orbitals are not deeply buried and participate in bonding to a greater extent.
(ii) Oxidation states
The principal oxidation state of lanthanoids is (+3). However, sometimes we also encounter oxidation states of + 2 and + 4. This is because of extra stability of fully-filled and half-filled orbitals. Actinoids exhibit a greater range of oxidation states. This is because the 5f, 6d, and 7s levels are of comparable energies. Again, (+3) is the principal oxidation state for actinoids. Actinoids such as lanthanoids have more compounds in +3 state than in +4 state.
(iii) Atomic and lonic sizes
Similar to lanthanoids, actinoids also exhibit actinoid contraction (overall decrease in atomic and ionic radii). The contraction is greater due to the poor shielding effect of 5f orbitals.
(iv) Chemical reactivity
In the lanthanide series, the earlier members of the series are more reactive. They have reactivity that is comparable to Ca. With an increase in the atomic number, the lanthanides start behaving similar to Al. Actinoids, on the other hand, are highly reactive metals, especially when they are finely divided. When they are added to boiling water, they give a mixture of oxide and hydride. Actinoids combine with most of the non-metals at moderate temperatures. Alkalies have no action on these actinoids. In case of acids, they are slightly affected by nitric acid (because of the formation of a protective oxide layer).
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Concepts Used:
Actinoids
Actinoids are a series of elements in the periodic table that have atomic numbers ranging from 89 to 103. These elements are also known as the actinides or the actinide series. They are located in the second row at the bottom of the periodic table, below the lanthanoid series.
The actinoids are all radioactive, with the exception of thorium, and most of them are synthetic, meaning they do not occur naturally on Earth. They are typically found in nuclear reactors or in laboratory experiments.
The actinoids have similar properties to the lanthanoids, as they both have f-electrons that are partially filled. However, the actinoids are generally more reactive and have a greater range of oxidation states compared to the lanthanoids. They also have a greater tendency to form complex ions and compounds.
The actinoids are of great importance in nuclear technology and chemistry, as they are used in nuclear reactors and in the production of nuclear weapons. They also have potential applications in areas such as medical imaging and cancer treatment. However, their radioactive nature means that they can also be highly toxic and pose a significant environmental risk if not handled properly.