This is the most deceptively simple concept in the chapter. The NCERT solution states: As atomic number increases, the atomic radius decreases slightly because of poor shielding by f-electrons.
Why does scandium not exhibit variable oxidation states? D And F Block Elements Class 12 Ncert Solutions
Because they are the diplomats of the periodic table. They offer a surface — a neutral ground where reactant molecules can hold hands. Iron in the Haber process doesn’t just sit there; its d-orbitals reach out, weakly grab N₂ and H₂, weaken their bonds, and let them react. The NCERT solution says "because they form intermediate complexes." The deep story says: They are the hosts of a molecular party, inviting guests to dance, then stepping away once the new bond is formed. If the d-block is a bustling city, the f-block is a monastery deep in the mountains — silent, powerful, and rarely understood. NCERT introduces them almost as an afterthought, but their story is profound. This is the most deceptively simple concept in the chapter
Imagine the periodic table as a grand medieval city. The main streets (s-block) hold the reactive, flashy metals — the crowd-pleasers. The right side (p-block) is the industrial district, full of gases and brittle solids. But beyond the main square, down a shadowed alley guarded by a gate called "Transition," lies the d-block . And past that, in a forgotten wing behind a locked door labeled "f-block," lie the inner sanctuaries — the lanthanoids and actinoids. Because they are the diplomats of the periodic table
A shallow answer: Because it has only one d-electron. The deep story: Scandium is like a child with a single toy. It can give away that toy (Sc³⁺) and become stable, but it cannot juggle. Manganese, on the other hand, has five d-electrons — it can lose 2, 3, 4, 5, 6, or even 7 electrons, each time revealing a new persona: Mn²⁺ (pale pink), Mn⁴⁺ (brown), Mn⁷⁺ (deep green in permanganate). The NCERT solutions ask you to calculate these states, but the real learning is to visualize the d-orbital as a stage where electrons perform a drama of oxidation and reduction.