Properties of f-block elements

• i. Properties are similar to d block elements
• ii. Electrons are added to f subshells of the (n-2) level
• iii. Placed between (n-1)d and ns block elements

Lanthanoids begin with atomic number 57 and end at 71. Although, historically, lanthanoids are termed as rare earth elements, they are fairly abundant in the earth's crust. For example, thulium is found more in abundance than silver ($\mathrm{4.5 \times 10^{-5}}$ vs $\mathrm{0.79 \times 10^{-5}}$ percent by mass). The name rare earth elements was coined because of the difficulty in extracting them economically in pure form from other lanthanoids having similar chemical properties. Now, due to newer separation methods like ion exchange resins, the separation of these elements has become easier and more economical.

These metals are soft, with moderate densities of about 7 g cm⁻³. They have high melting (~1000 $\mathrm{^{0}C}$) and boiling points (~3000 $\mathrm{^{0}C}$). Similar to groups 1 and 2, lanthanoids in the metallic state are very reactive, and resemble alkali and alkaline earth metals in their reactivities more than transition metals. For example, they react with water to give the metal hydroxide and hydrogen gas

Although the common oxidation state for lanthanoids is +3, the +2 oxidation state is also important. They all form stable oxides of the type $\mathrm{M_2O_3}$, where M is the metal ion. $\mathrm{Eu^{2+}}$ and $\mathrm{Yb^{2+}}$ are the most stable dipositive metal ions. Higher oxidation states are unusual for lanthanoids, with the only exception of cerium, which forms a stable +4 species. The energy required to break up the metal lattice is the heat of atomization. Lanthanoids have lower heat of atomization than transition metals. This is because, with d electrons, transition metals are much harder and require a high heat of atomization. Europium and ytterbium have the lowest enthalpies of vaporization and the largest atomic radii of the lanthanoids, and resemble barium. These two elements resemble alkaline earth elements; they dissolve in liquid ammonia to give blue conducting solutions.

Their ionic radii decrease from 117 pm of La to 100 pm for Lu. This is because 5f orbitals do not shield the outer 5s and 5p electrons effectively, leading to an increase in effective nuclear charge and a decrease in the ionic size (so the book's own sentence — for the lanthanoids the inner subshell being filled is 4f). Such large ions have a higher coordination number, which varies from 6 (most common) to 9, 10 and up to 12 in some cases. For example, the hydrated lanthanum ion is a nonahydrate, $\mathrm{[La(H_2O)_9]^{3+}}$.

All the lanthanoids form hydroxides of the general formula $\mathrm{Ln(OH)_3}$ (Ln represents any element of the lanthanoid series). These are ionic and basic. Since the ionic size decreases from $\mathrm{La^{3+}}$ to $\mathrm{Lu^{3+}}$, the basicity of the hydroxides decreases: $\mathrm{La(OH)_3}$ is the strongest base, while $\mathrm{Lu(OH)_3}$ is the weakest base. …