Question

Observe the following statements.
1. Lanthanides actively participate in chemical reactions.
2. The basic nature of hydroxides of lanthanides increases from \[\text{La}{{\left( \text{OH} \right)}_{\text{3}}}\] to\[\text{Lu}{{\left( \text{OH} \right)}_{\text{3}}}\].
 3. Lanthanides do not form coordinate compounds as readily as d-block metals.

The correct statements are:
A) 1, 2&3
B) 1&3
C) 1&2
D) 2&3

Answer 1

Hint: In lanthanides, the steady decrease in atomic radii and ionic sizes of lanthanide elements with increasing atomic number is called as lanthanide contractions. Lanthanides are a good reducing agent and have a high chemical reactivity. Due to lanthanide contraction, the covalent character between the lanthanides and the hydroxyl ions increases.

Complete step by step answer:
1. We know that all the lanthanides are highly electropositive metals and have almost similar chemical reactivity. This is because the lanthanides differ only in the number of \[\text{4f}\] electrons. The \[\text{4f}\] electrons are effectively shielded from the other elements by the overlapping of\[\text{5s}\], \[\text{5p}\]and \[\text{6s}\] electrons. They show the difference in their chemical reactivity. This is because the similar chemical reactivity's separation from one another is very difficult. Lanthanides have high negative ${{\text{E}}_{\text{0}}}$. They are good reducing agents. In the lanthanide series, the reactivity is similar to the calcium but with the increasing atomic number they behave as an aluminium. The emf values for the half-reaction are in the range of$\text{-2}\text{.2 to -2}\text{.4V}$.
$\text{Ln}_{\text{aq}}^{\text{3+}}\text{+3}{{\text{e}}^{\text{-}}}\to \text{L}{{\text{n}}_{\text{(s)}}}$
Hence the 1) statement is true about the lanthanides.

2. In lanthanides with increasing atomic numbers the atomic and ionic radii of the element decrease from one element to another. The steady decrease in the atomic and ionic size of the lanthanide element series with increasing atomic number is called the lanthanide contraction.
Due to lanthanide contraction, the size of the lanthanide decreases regularly. As a result, the covalent character between the lanthanide ions and that of the $\text{O}{{\text{H}}^{\text{-}}}$ ions increases from the$\text{L}{{\text{a}}^{\text{3+}}}$ to $\text{L}{{\text{u}}^{\text{3+}}}$ in basic lanthanide oxides. The basic strength is found to be inversely related to the atomic number. Thus $\text{La(OH}{{\text{)}}_{\text{3}}}$ is more basic and $\text{Lu(OH}{{\text{)}}_{\text{3}}}$ is less basic.
Therefore the given statement 2) is wrong about the lanthanide oxides.

3. Like lanthanides, the actinides also form the complexes. In lanthanides, the $\text{4f}$orbitals are well shielded by the Complex formation by lanthanides that is different from that of actinides. In lanthanides, the $\text{4f}$ orbitals are well shielded by the larger \[\text{5d}\]and\[\text{6s}\] orbitals. Thus the f-orbitals do not take part in the complex formation. However, in actinides, the $\text{5f}$ orbitals of actinides are outward and are not well shielded, thus do take part in the interaction of complexes easily. This is also because of the higher charge and smaller size of actinides too.
Therefore statement 3) is true about the lanthanide and actinides.
So, the correct answer is “Option B”.

Note: Like lanthanide, actinides also undergo the contraction which is also called the actinide contraction. Remember that along with the series the atomic number increases and atomic size decreases. This is completely different from the trend we observe in groups.