Test: Lanthanide- 1 - Chemistry MCQ

• Lanthanide contraction is the gradual decrease in the atomic and ionic size of lanthanoids with an increase in atomic number.
• The Lanthanide Contraction is caused by a poor shielding effect of the 4f electrons.

• Due to lanthanide contraction as the size of lanthanide ions decreases from La³⁺ to Lu³⁺, the covalent character of the hydroxides increases, and hence the basic strength decreases. 
• Thus, La(OH)₃ is the most basic, and Lu(OH)₃ is the least basic.

• Lanthanide contraction is the gradual decrease in the atomic and ionic size of lanthanoids with an increase in atomic number.
• The Lanthanide Contraction is caused by a poor shielding effect of the 4f electrons.

• Lanthanides of the first f-block have a terminal electronic configuration:
  [Xe] 4f^1-14 5d^0-1 6s².
• There is an exception in the case of gadolinium, Gd (Z = 64) where the electron enters the 5d orbital due to the presence of half-filled d-orbital

• 'La' forms compounds in which its oxidation no. is +3.
• 'Eu' and 'Gd' exhibit +2 as well as +3 oxidation state and not higher than that. due to stable (f⁷) configuration.
• 'Am' exhibits the oxidation states +2, +3, +4, +5, +6, etc. due to extremely large size and low ionization energy.

• The incorrect statement about the Cerium is only the B option.
  B: The +4 oxidation state of cerium is not known in solutions.
  As +4 oxidation state, is common for the Cerium.
• The correct statements about the Cerium are as follows:
  A: Cerium (IV) acts as an oxidizing agent
  C: The common oxidation state of Cerium are +3 and +4.
  D: The +3 oxidation state of the Cerium is more stable than the +4 oxidation state.

• Lanthanide contraction is the gradual decrease in the atomic and ionic size of lanthanoids with an increase in atomic number.
• The Lanthanide Contraction is caused by a poor shielding effect of the 4f electrons.

• Lanthanides have the configuration of [Xe]4f¹⁻¹⁴ 5d¹ 6s²
• So their trivalent ion has the configuration of [Xe]4f¹ to [Xe]4f¹⁴

• Lanthanides show variable oxidation states.
• The most stable oxidation state of Lanthanides is +3.
• They also show +2 and +4 oxidation states due to the presence of either half-filled or completely filled or empty 4f sub-shell.

• Lanthanoid for which +2 and +3 oxidation states are common is Eu.
• La has +3 oxidation state. Ce has +3 and +4 oxidation states. Nd has +2, +3 and +4 oxidation state.

The common oxidation state of Cerium are +3 and +4.

• Lanthanide contraction is the gradual decrease in the atomic and ionic size of lanthanoids with an increase in atomic number.
• The Lanthanide Contraction is caused by a poor shielding effect of the 4f electrons.

The atomic radius of the metal zirconium, Zr, (a period-5 transition element) is 159 pm and that of hafnium, Hf, (the corresponding period-6 element) is 156 pm. The ionic radius of Zr4+ is 79 pm and that of Hf4+ is 78 pm. The radii are very similar even though the number of electrons increases from 40 to 72 and the atomic mass increases from 91.22 to 178.49 g/mol.

This is due to Lanthanide contraction i.e. greater-than-expected decrease in ionic radii of the elements in the lanthanide series from atomic number 57, lanthanum, to 71, lutetium, which results in smaller than otherwise expected ionic radii 

Correct option is B)

Electronic configuration of [Gd]³⁺:[Xe]4f⁷

Hence number of unpaired electron n=7

Hence, magnetic moment=n(n+2)​=63​=7.9BM