d and f BLOCK ELEMENTS

Why do the complexes [Ti(H2O)6]^3+ and [V(H2O)6]^3+ have different colors in aqueous solution?

• Because Ti and V are different metals.
• Because they have different charges.
• Because H2O is a ligand.
• Because Ti^3+ (d^1) and V^3+ (d^2) have different numbers of d-electrons, leading to different d-orbital occupancy and different crystal field splitting energies, absorbing different wavelengths of light.

Why do the third ionization enthalpies of Fe, Co, and Ni show a relatively steady increase compared to the more irregular pattern seen for earlier transition metals?

• Because Fe, Co, and Ni are metals.
• Because they have higher atomic numbers.
• Because removing the third electron from Fe^2+ (d^6), Co^2+ (d^7), and Ni^2+ (d^8) involves removing an electron from increasingly filled d-orbitals, without disrupting particularly stable configurations like d^5 or d^10.
• Because they are located at the end of the series.

Why do the complexes [Ni(CO)4] and [Ni(CN)4]^2- have different geometries?

• Because CO and CN- are different ligands.
• Because they have different charges.
• Because Ni has different oxidation states.
• Because the different ligands (CO vs CN-) and the different oxidation states of Ni (0 vs +2) result in different numbers of d-electrons and different ligand field strengths, favoring different geometries.

Why do the first row transition metals generally form fewer stable compounds with very high coordination numbers (e.g., CN > 6) compared to second and third row transition metals?

• Because first row metals are less reactive.
• Because first row metals have fewer d-electrons.
• Because first row metals are lighter.
• Because the smaller size of first row metals makes it sterically difficult to accommodate a large number of ligands around the central metal ion.

Why do the atomic orbitals of 5d elements contract compared to 4d elements, despite having an additional electron shell?

• Because 5d elements are heavier.
• Because the nuclear charge increases.
• Because 5d elements are metals.
• Because relativistic effects become significant for elements with high atomic numbers, causing the 5d orbitals to shrink in size.