Question

Discuss the consequences of lanthanide contraction.

Answer 1

Hint: Lanthanide contractions are caused due to the imperfect shielding in 4f subshell, found in 4f series present in the bottom of the periodic table; and known to be lanthanide series. The factors like atomic size, complex formation, ionization energy of d-block elements, basic strength of hydroxides formed predicts the effect of lanthanide contraction. Now, we can discuss the consequences of lanthanide contraction.

Complete step by step solution:
> First, we will know about the lanthanide contractions. There is a gradual increase in size with an increase in atomic number from La to Lu, as there is increase in nuclear charge, and the atomic size decreases gradually for the tri positive lanthanide ions.
> As mentioned, there are several factors predicting the effect of lanthanide contraction. Let us discuss the atomic size.
> If we talk about the atomic size, the radius of Zr, and Hf are equal; and radius of Nb, and Ta are equal; it means that the size of atoms belonging to the third transition series is approximately the same to that of the second transition series.
> As we know the smaller size of lanthanides, higher the nuclear charge. Thus, the tendency to form coordinate complexes increases.
> The ionization energy is much higher due to the higher nuclear charge.
As we know, lanthanides exhibit the +3 oxidation state, so the covalent character increases, and hence there is a decrease in basic strength.
> Now, in the end we can conclude that the nuclear charge, and atomic size mainly causes the lanthanide contractions.

Note: Don’t get confused in between the lanthanide, and actinide contractions. The both are present in the bottom of the periodic table; but the lanthanide contractions are found in 4f series, whereas actinide contractions are found in 5f series.