(A) The basic nature of hydroxides of lanthanoid elements decreases moving from left to right. Explain

Question

Read the given paragraph and given answer of the following questions.

The rare earth elements of the modern periodic table are known as lanthanoids. They have separate block in periodic table. The lanthanoid series consist of fourteen elements starting from Cerium (atomic number – 58) to Lutetium (atomic number - 71). All lanthanoids generally exhibit +3 oxidation state. In addition some lanthanoids show +2 and +4 oxidation state also. As we move from left to right in lanthanoid series there is regular decrease in the size of an atom. This is known as lanthanoid contraction. There are many industrial application as – formation of mischmetal, production of parts of Jet engine.

(A) The basic nature of hydroxides of lanthanoid elements decreases moving from left to right. Explain.  

(B) Write name of two lanthanoid elements used in the formation of mischmetal.

(C)  Write the name of one lanthanoid element exhibiting +4 oxidation state.  

Answer 1

(A)  With an increase in the atomic number ,the basic strength of the oxides and hydroxides decreases. This contraction causes as decrease in the size of lanthanoide cations and, therefore, the polarizing power of the cations increases. This further decreases the ionic character of the oxides and hydroxides. Thus, Ce(OH)₄ is maximum and Lu(OH)₄ is least basic .

(B)  Ce (Cerium) and La (Lanthanum)

(C)  Ce (Cerium) Form Ce⁺⁴