d and f BLOCK ELEMENTS

Why do the complexes [Co(NH3)6]^3+ and [CoF6]^3- exhibit different magnetic properties?

• Because they have different charges.
• Because NH3 and F- are different ligands.
• Because Co^3+ is paramagnetic.
• Because NH3 is a strong field ligand leading to a low-spin configuration, while F- is a weak field ligand leading to a high-spin configuration, resulting in different numbers of unpaired electrons.

Why do the +5 and +6 oxidation states become less stable relative to +4 and +3 as we move from the early to the later members of the actinoid series?

• Because later actinoids are heavier.
• Because later actinoids are more radioactive.
• Because the nuclear charge decreases.
• Because the increasing nuclear charge and relativistic effects in later actinoids make it energetically more costly to remove the large number of electrons required for the high +5 and +6 states.

Why do the +2 oxidation states become more stable relative to +3 as we move from the beginning to the end of the lanthanoid series?

• Because the nuclear charge increases.
• Because the 4f electrons are added.
• Because the +2 state is always more stable.
• Because achieving the +2 state for elements like Yb ([Xe] 4f^14) results in a particularly stable filled 4f subshell, making the +2 state increasingly favorable compared to the +3 state.

Why do the compounds of later actinoids tend to be more covalent in character compared to those of earlier actinoids?

• Because later actinoids are heavier.
• Because later actinoids are more radioactive.
• Because later actinoids are metals.
• Because the 5f orbitals contract and become more similar in size to the 6d orbitals in later actinoids, allowing for greater orbital overlap and covalent bonding.

Why do the atomic radii of the +3 ions of lanthanoids decrease steadily across the series (Lanthanoid contraction)?

• Because the nuclear charge decreases.
• Because the electrons are removed.
• Because the 4f electrons added across the series provide very poor shielding for the outer electrons from the increasing nuclear charge, causing the outer electrons to be pulled closer.
• Because they are lanthanoids.