Key Points

Transition metals are elements in groups 3-12 of the periodic table. According to IUPAC, they are defined as elements having an incomplete d subshell either in their neutral atom or in their common ions.

The general outer electronic configuration of d-block elements is $(n-1)d^{1-10} ns^{1-2}$. Exceptions like Cr ($3d^5 4s^1$) and Cu ($3d^{10} 4s^1$) exist due to the extra stability of half-filled and fully-filled d orbitals.

Zinc (Zn), Cadmium (Cd), and Mercury (Hg) are not considered transition metals because they have a completely filled $d^{10}$ configuration in both their ground state and their common oxidation state ($+2$).

Transition metals exhibit a wide range of oxidation states because the energy difference between the $(n-1)d$ and $ns$ orbitals is small, allowing electrons from both subshells to participate in bonding.

Most transition metal ions are paramagnetic due to the presence of unpaired electrons. The magnetic moment ($\mu$) can be calculated using the spin-only formula: $\mu = \sqrt{n(n+2)}$ Bohr Magnetons (BM), where n is the number of unpaired electrons.

Transition metal ions are often coloured because the energy required for an electron to jump from a lower to a higher energy d orbital (d-d transition) corresponds to the frequency of visible light. The observed colour is the complement of the light absorbed.

Transition metals and their compounds act as excellent catalysts due to their ability to adopt multiple oxidation states and form intermediate complexes, providing an alternative reaction pathway with lower activation energy.

These elements form a large number of complex compounds due to the small size of their ions, high ionic charges, and the availability of vacant d orbitals for forming coordinate bonds with ligands.

Transition metals form interstitial compounds by trapping small atoms like H, C, or N in their crystal lattice. They also readily form alloys with other metals due to their similar atomic radii.

The f-block elements consist of two series: the lanthanoids (4f series) and the actinoids (5f series). In these elements, the last electron enters the f-orbitals of the anti-penultimate shell.

Lanthanoid contraction is the steady decrease in atomic and ionic radii across the lanthanoid series. This is caused by the poor shielding effect of the 4f electrons, which fails to compensate for the increasing nuclear charge.

Due to lanthanoid contraction, the atomic radii of the second (4d) and third (5d) transition series are very similar. This makes the separation of elements like Zirconium (Zr) and Hafnium (Hf) very difficult.

Actinoid contraction is a similar decrease in size across the actinoid series, but it is greater than lanthanoid contraction due to poorer shielding by 5f electrons. Actinoids also show a wider range of oxidation states and are all radioactive.

Potassium dichromate is a strong oxidizing agent, especially in acidic solutions. The dichromate ion ($Cr_2O_7^{2-}$), which is orange, gets reduced to the green chromic ion ($Cr^{3+}$). The reaction is: $Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O$.

Potassium permanganate is a very strong oxidizing agent whose action depends on the pH of the solution. In an acidic medium, the purple permanganate ion ($MnO_4^-$) is reduced to the colorless manganous ion ($Mn^{2+}$): $MnO_4^- + 8H^+ + 5e^- \rightarrow Mn^{2+} + 4H_2O$.

The most common and stable oxidation state for all lanthanoids is $+3$. However, some elements show $+2$ (e.g., $Eu^{2+}$) or $+4$ (e.g., $Ce^{4+}$) states, which are associated with the stability of empty, half-filled, or fully-filled f-orbitals.