Which of the following statements concerning lanthanides elements is f...
**Explanation:**
The correct statement among the given options is **option A** - "Ionic radii of trivalent lanthanides steadily increase with an increase in the atomic number." This statement is **FALSE**.
**Ionic Radii of Trivalent Lanthanides:**
- The lanthanides are a series of 15 elements, from lanthanum (atomic number 57) to lutetium (atomic number 71), that are located in the f-block of the periodic table.
- The lanthanides have similar electronic configurations, with a partially filled 4f subshell.
- The 4f electrons are shielded by the 5s and 5p electrons, so they do not significantly influence the atomic radius or the ionic radius of the trivalent lanthanides.
- The ionic radii of the trivalent lanthanides are almost constant across the series, with only slight variations.
- This is because the 4f electrons are localized close to the nucleus and do not contribute significantly to the atomic or ionic size.
- The ionic radii of the trivalent lanthanides are smaller than those of the corresponding divalent lanthanides because of the higher effective nuclear charge experienced by the trivalent ions.
**Other Statements:**
a) Ionic radii of trivalent lanthanides steadily increase with an increase in the atomic number. (False)
b) Lanthanides are separated from one another by ion exchange method. (True)
c) All lanthanides are highly dense metals. (True)
d) The most characteristic oxidation state of lanthanides elements is 3. (True)
**Conclusion:**
The false statement among the given options is option A. The ionic radii of trivalent lanthanides do not steadily increase with an increase in the atomic number. Instead, their ionic radii are almost constant across the series.
Which of the following statements concerning lanthanides elements is f...
Because in the period, with increase in number of electrons in the "f" orbitals, the nuclear attraction over the outermost electrons increases as the screening effect of f orbitals over nuclear attraction is poor. So ionic radii decreases as the atomic number increases in lanthanides.