Lanthanoids generally show high chemical reactivity, similar to alkaline earth metals, although the initial members are more reactive.

Ionisation Enthalpies generally increase across the series due to increasing nuclear charge, but irregularities exist due to changes in shielding and orbital stability.

The d-block elements are positioned between the s and p blocks, specifically in groups 3 to 12.

Actinoids have a greater tendency to form complexes compared to Lanthanoids, largely due to their smaller ionic sizes and higher charges.

The similar radii of 4d and 5d elements are a consequence of the Lanthanoid Contraction, which is caused by the poor shielding effect of the 4f electrons.

Actinoids show a greater range of oxidation states than Lanthanoids due to the small energy difference between 5f, 6d, and 7s orbitals.

These are known as Interstitial Compounds.

Transition elements are often used as catalysts due to their variable oxidation states and ability to form reactive intermediates.

One of the general characteristics of Actinoids is that all of them are radioactive.

Transition elements exhibit strong metallic bonding due to the presence of a large number of unpaired electrons in the (n−1)d orbitals, resulting in high melting and boiling points.

Paramagnetism and colour require the presence of unpaired electrons (partially filled d or f orbitals). Sc³⁺ is d⁰ (no unpaired electrons), hence it is diamagnetic and colourless.

The contraction is due to the imperfect (poor) shielding of the increasing nuclear charge by the newly added 4f electrons.

The electronic configurations of the d-block elements involve the filling of the (n-1)d orbitals, which generally range from (n−1)d1−10ns1−2

Transition metals form alloys readily because their atomic sizes are very similar and comparable, allowing atoms to substitute one another in the metallic lattice.

Lanthanoids primarily exhibit the +3 oxidation state, which is the most stable state for most elements in this series.

Transition metals form complexes due to their small size, high ionic charges, and the availability of vacant d-orbitals to accept electron pairs from ligands.

The formation of coloured ions is due to the absorption of radiation in the visible region, causing d-d transitions (excitation of electrons from one d-orbital to another).

In lower oxidation states, the compounds are generally more ionic and hence basic, as the polarizing power of the metal decreases.

Transition metals utilize both the ns and (n-1)d electrons because the energy difference between these orbitals is small, leading to variable oxidation states.

Lanthanoid Contraction is the steady decrease in the size of the Ln³⁺ ions (and atomic radii) with an increase in atomic number across the Lanthanoid series.

Cerium (Ce) is the first element of the Lanthanoid series, hence it is an f-block element.

Catalytic activity is due to the ability of transition metals to exhibit variable oxidation states and form intermediate compounds, as well as their large surface area.

The E∘ values for the M2+ couple tend to show an irregular trend, but generally, transition metals are strong reducing agents.

The energies of the 5f, 6d, and 7s orbitals are comparable, leading to complexity in their electronic configuration and oxidation states.

Manganese exhibits a maximum oxidation state of +7 in compounds like KMnO₄.

In acidic solution, MnO₄⁻ (Mn in +7 state) is reduced to the stable Mn²⁺ ion.

Actinoids exhibit a larger range of oxidation states, extending up to +7 (e.g., Np, Pu), which is not typical for Lanthanoids.

Potassium Dichromate is prepared from chromite ore (FeCr₂O₄).

Paramagnetism is a consequence of the presence of unpaired electrons in the d-orbitals.

The Lanthanoids involve the filling of the 4f orbitals.