Chemistry · Ch 8 — Transition and Inner Transition Elements

Properties of Lanthanoids

8.12

Properties of Lanthanoids

i. Soft metals with silvery white colour and moderate densities of ~ 7 g cm⁻³. Colour and brightness reduces on exposure to air
ii. Good conductors of heat and electricity.
iii. Except promethium (Pm), all are non-radioactive in nature.
iv. The atomic and ionic radii decrease from lanthanum (La) to lutetium (Lu). This is known as lanthanoid contraction.
v. Binding to water is common (i.e.) such that $\mathrm{H_2O}$ is often found in products when isolated from aqueous solutions.
vi. Coordination numbers usually are greater than 6, typically 8, 9,... (up to 12 found).
vii. The lanthanoids are strongly paramagnetic (printed "lanthanoides"). Gadolinium becomes ferromagnetic below 16 $\mathrm{^{0}C}$ (Curie point). The other heavier lanthanoids — terbium, dysprosium, holmium, erbium, thulium, and ytterbium — become ferromagnetic at much lower temperatures.
viii. Magnetic and optical properties are largely independent of environment (similar spectra in gas/solution/solid).

Table 8.11 : Electronic configuration and atomic ionic radii of lanthanoids (printed as a full-page table; the dotted cells "……" are the book's own blanks — the "Try this" task of section 8.12.1 asks you to fill them in)

Element	Symbol	Atomic number	Expected (ground state)	Observed (ground state)	(+2 oxidation state)	(+3 oxidation state)	Atomic radii, pm	Ionic radii ( $\mathrm{Ln^{+3}}$ , 6-coordinate), pm
Lanthanum	La	57	$\mathrm{[Xe]4f^{0}5d^{1}6s^2}$	$\mathrm{[Xe]4f^{0}5d^{1}6s^2}$	$\mathrm{4f^0,5d^1}$	$\mathrm{4f^0}$	187	103
Cerium	Ce	58	$\mathrm{[Xe]4f^{2}6s^2}$	$\mathrm{[Xe]4f^{1}5d^{1}6s^2}$	$\mathrm{4f^2}$	$\mathrm{4f^1}$	183	102
Praseodymium	Pr	59	$\mathrm{[Xe]4f^{3}6s^2}$	$\mathrm{[Xe]4f^{3}6s^2}$	$\mathrm{4f^3}$	$\mathrm{4f^2}$	182	99
Neodymium	Nd	60	$\mathrm{[Xe]4f^{4}6s^2}$	$\mathrm{[Xe]4f^{4}6s^2}$	$\mathrm{4f^4}$	……	181	98.3
Promethium	Pm	61	$\mathrm{[Xe]4f^{5}6s^2}$	$\mathrm{[Xe]4f^{5}6s^2}$	$\mathrm{4f^5}$	……	181	97
Samarium	Sm	61	$\mathrm{[Xe]4f^{6}6s^2}$	$\mathrm{[Xe]4f^{6}6s^2}$	$\mathrm{4f^6}$	$\mathrm{4f^5}$	180	95.8
Europium	Eu	63	$\mathrm{[Xe]4f^{7}6s^2}$	$\mathrm{[Xe]4f^{7}6s^2}$	$\mathrm{4f^7}$	$\mathrm{4f^6}$	199	94.7
Gadolinium	Gd	64	$\mathrm{[Xe]4f^{8}6s^2}$	$\mathrm{[Xe]4f^{7}5d^{1}6s^2}$	$\mathrm{4f^7,5d^1}$	……	178	93.8
Terbium	Tb	65	$\mathrm{[Xe]4f^{9}6s^2}$	$\mathrm{[Xe]4f^{9}6s^2}$	$\mathrm{4f^9}$	$\mathrm{4f^8}$	177	92.3
Dysprosium	Dy	66	$\mathrm{[Xe]4f^{10}6s^2}$	$\mathrm{[Xe]4f^{10}6s^2}$	$\mathrm{4f^{10}}$	$\mathrm{4f^9}$	176	91.2
Holmium	Ho	67	$\mathrm{[Xe]4f^{11}6s^2}$	$\mathrm{[Xe]4f^{11}6s^2}$	$\mathrm{4f^{11}}$	$\mathrm{4f^{10}}$	175	90.1
Erbium	Er	68	$\mathrm{[Xe]4f^{12}6s^2}$	$\mathrm{[Xe]4f^{12}6s^2}$	$\mathrm{4f^{12}}$	……	174	89

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