Chemistry · Ch 8 — Transition and Inner Transition Elements

Applications of actinoids

8.16

Applications of actinoids

We have seen that the half-lives of natural thorium and uranium isotopes are so long that we get very negligible radiation from these elements. We find them in everyday use. For example, Th(IV) oxide, $\mathrm{ThO_2}$ , with 1% $\mathrm{CeO_2}$ was used as a major source of indoor lighting before incandescent lamps came into existence — only because these oxides convert heat energy from burning natural gas to an intense light. Even today there is a great demand for these lights for outdoor camping.

Note

Do you know ? Uranium is another actinoid which is in great demand, as it is used in nuclear reactors. One of the extraction methods for uranium has a very interesting chemistry. The ore containing U(IV) oxide, $\mathrm{UO_2}$ , is first treated with Fe(III) ion to give U(VI) oxide, $\mathrm{UO_3}$ :

$\mathrm{UO_2\,(s) + H_2O({\it l}) \longrightarrow UO_3\,(s) + 2H^{+}\,(aq) + 2e^{-}}$

$\mathrm{Fe^{3+}\,(aq) + e^{-} \longrightarrow Fe^{2+}\,(aq)}$

Addition of $\mathrm{H_2SO_4}$ to this solution produces uranyl sulphate, containing the $\mathrm{UO_2^{2+}}$ cation:

$\mathrm{UO_3\,(s) + H_2SO_4\,(aq) \longrightarrow UO_2SO_4\,(aq) + H_2O\,({\it l})}$

After purification, ammonia is added to the solution, giving a bright yellow precipitate of ammonium diuranate, $\mathrm{(NH_4)_2U_2O_7}$ :

$\mathrm{2\,UO_2SO_4\,(aq) + 6\,NH_3\,(aq) + 3\,H_2O\,({\it l}) \longrightarrow (NH_4)_2U_2O_7\,(s) + 2\,(NH_4)_2SO_4\,(aq)}$

This yellow cake is the marketable form of uranium!

Similarities and differences between lanthanoids and actinoids

Similarities	Differences
Both the series show a +3 oxidation state	Lanthanoids show a maximum oxidation state of +4 while actinoids show oxidation states of +3, +4, +5, +6 and +7
In both the series, the f-orbitals are filled gradually	Lanthanoids do not form complexes easily. Actinoids have a greater tendency to form complexes with ligands such as thioethers
Ionic radii of the elements in both series decreases with an increase in atomic number	All lanthanoids are non-radioactive except promethium but actinoids are radioactive in nature
The electronegativity of all the elements in both the series is low and are said to be highly reactive	Lanthanoids do not form oxocations, but actinoids form oxocations such as $\mathrm{UO^{+}}$ , $\mathrm{PuO^{+}}$ , $\mathrm{NpO_2^{+}}$
The nitrates, perchlorates and sulphates of all the elements are soluble while the hydroxides, fluorides and carbonates are insoluble	Most of the lanthanoids are colourless in nature whereas the actinoids are coloured ions

Table 8.14 Electronic configuration of actinoids and their ionic radii in +3 oxidation state (the book's ionic-radii column header prints "(Ac³⊕)")

Element	Symbol	Atomic number	Ground state configuration	+3 oxidation state	Atomic radii, pm	Ionic radii, pm
Actinium	Ac	89	$\mathrm{[Rn]5f^{\,0}6d^{1}7s^2}$	$\mathrm{5f^{\,0}}$	203	126
Thorium	Th	90	$\mathrm{[Rn]5f^{\,0}6d^{2}7s^2}$	$\mathrm{5f^{\,1}}$	180	-
Protactinium	Pa	91	$\mathrm{[Rn]5f^{\,2}6d^{1}7s^2}$	$\mathrm{5f^{\,2}}$	162	118
Uranium	U	92	$\mathrm{[Rn]5f^{\,3}6d^{1}7s^2}$	$\mathrm{5f^{\,3}}$	153	118
Neptunium	Np	93	$\mathrm{[Rn]5f^{\,4}6d^{1}7s^2}$	$\mathrm{5f^{\,4}}$	150	116
Plutonium	Pu	94	$\mathrm{[Rn]5f^{\,6}6d^{0}7s^2}$	$\mathrm{5f^{\,5}}$	162	115
Americium	Am	95	$\mathrm{[Rn]5f^{\,7}6d^{0}7s^2}$	$\mathrm{5f^{\,6}}$	173	114
Curium	Cm	96	$\mathrm{[Rn]5f^{\,7}6d^{1}7s^2}$	$\mathrm{5f^{\,7}}$	174	112
Berkelium	Bk	97	$\mathrm{[Rn]5f^{\,9}6d^{0}7s^2}$	$\mathrm{5f^{\,8}}$	170	110
Californium	Cf	98	$\mathrm{[Rn]5f^{\,10}6d^{0}7s^2}$	$\mathrm{5f^{\,9}}$	186	109
Einsteinium	Es	99	$\mathrm{[Rn]5f^{\,11}6d^{0}7s^2}$	$\mathrm{5f^{\,10}}$	186	98
Fermium	Fm	100	$\mathrm{[Rn]5f^{\,12}6d^{0}7s^2}$	$\mathrm{5f^{\,11}}$	198	91
Mendelevium	Md	101	$\mathrm{[Rn]5f^{\,13}6d^{0}7s^2}$	$\mathrm{5f^{\,12}}$	194	90
Nobelium	No	102	$\mathrm{[Rn]5f^{\,14}6d^{0}7s^2}$	$\mathrm{5f^{\,13}}$	197	95
Lawrencium	Lr	103	$\mathrm{[Rn]5f^{\,14}6d^{1}7s^2}$	$\mathrm{5f^{\,14}}$	171	88

Table 8.15 : Some comparison between s - block, Lanthanoids and Transition Metals

s - block Metals	Lanthanoids	Transition Metals
Essentially monovalent - show group (n+) oxidation state	Essentially in (+3) oxidation state (+2/+4 for certain configurations)	Show variable oxidation states

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