Question

Knowing that the chemistry of lanthanides (Ln) is dominated by its +3 oxidation state, which of the following statements are correct?
a.) The ionic size of Ln (III) decreases in general with increasing atomic number.
b.) In (III) compounds are generally colourless.
c.) Ln (III) hydroxides are mainly basic in character.
d.) Because of the large size of the Ln (III) ions, the bonding in its compounds is predominantly ionic in character.

Answer 1

Hint: Lanthanides are the elements which are present in the first inner transition series. The starting element of this series is lanthanum. Hence, the series is known as lanthanide series.

Complete Solution :
- The lanthanides are the elements of the inner transition series. The inner transition elements are generally known as the f block elements because they involve the filling of the electrons in the f-orbital. In the lanthanide series the filling of 4f orbitals takes place.
- In the lanthanide series as the atomic number increases the ionic size of the lanthanide’s compounds present in +3 oxidation state decreases. This is due to the lanthanoid contraction.
- The +3 ions of the lanthanide series have unpaired f electrons. Hence, the In (III) compounds are generally coloured.
- The lanthanide hydroxides are basic in nature due to the presence of unpaired electrons in the f- orbital and due to the small electronegativity and large size of the ln(III) ions, the bonding in its compounds is predominantly ionic in character.
So, the correct answer is “Option i, ii, iv”.

Note: It must be noted that the electrons are filled according to the Aufbau principle which states that the electrons are filled in the order of their increasing energy level. The increasing energy level follows this order 1s, 2s, 2p, 3s, 3p, 4s, 3d and so on.