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Consider the following statements:
(I) The size of the lanthanide M3+ ions decreases as the atomic number of M increases.
(II) Electronic spectra of lanthanides show very broad band.
(III) As with transition metals, coordination number six is very common in lanthanide complexes.
Which of the statements given above is/are correct:
  • a)
    I only
  • b)
    III only
  • c)
    I and II
  • d)
    I and III
Correct answer is option 'D'. Can you explain this answer?
Most Upvoted Answer
Consider the following statements:(I) The size of the lanthanide M3+ i...
Statement I: The size of the lanthanide M3 ions decreases as the atomic number of M increases.
The lanthanide series consists of elements with atomic numbers ranging from 57 (lanthanum) to 71 (lutetium). As we move across the lanthanide series, the atomic number increases, which corresponds to an increase in the number of electrons. The lanthanide ions, M3+, are formed when three electrons are removed from the neutral lanthanide atoms.

As we move from lanthanum (La) to lutetium (Lu), the atomic radius of the lanthanide ions decreases. This is primarily due to the increase in effective nuclear charge as we move across the series. The increase in effective nuclear charge leads to a stronger attraction between the nucleus and the outermost electrons, resulting in a decrease in the atomic radius.

Therefore, Statement I is correct.

Statement II: Electronic spectra of lanthanides show very broad band.
The electronic spectra of lanthanides are characterized by broad bands rather than sharp lines. This is due to the presence of f-electrons in the outermost energy level of the lanthanide ions. The f-electrons are shielded by the 5s and 5p orbitals, which results in a poor overlap between the f-orbitals and the ligand orbitals. As a result, the energy levels of the f-electrons are less defined, leading to a broadening of the electronic spectrum.

This broadening of the spectrum is also influenced by the presence of crystal field splitting, which further spreads the energy levels of the f-electrons. The crystal field splitting arises from the interaction between the lanthanide ion and the ligands in a complex.

Therefore, Statement II is correct.

Statement III: As with transition metals, coordination number six is very common in lanthanide complexes.
The coordination number refers to the number of ligands bonded to the central metal ion in a complex. In transition metal complexes, coordination numbers of 4, 5, and 6 are commonly observed. However, in lanthanide complexes, coordination numbers of 6 and 8 are more common.

The larger size and higher charge density of lanthanide ions compared to transition metal ions allow for the accommodation of more ligands around the central metal ion. The lanthanide ions have a greater ability to form coordination complexes with larger coordination numbers.

Therefore, Statement III is incorrect.

In summary, the correct statements are:
- Statement I: The size of the lanthanide M3+ ions decreases as the atomic number of M increases.
- Statement II: Electronic spectra of lanthanides show very broad band.
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Consider the following statements:(I) The size of the lanthanide M3+ i...
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Consider the following statements:(I) The size of the lanthanide M3+ ions decreases as the atomic number of M increases.(II) Electronic spectra of lanthanides show very broad band.(III) As with transition metals, coordination number six is very common in lanthanide complexes.Which of the statements given above is/are correct:a)I onlyb)III onlyc)I and IId)I and IIICorrect answer is option 'D'. Can you explain this answer?
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