JEE Chemistry The D and F Block Elements Notes Set 01

General Properties of d-Block Elements

1. The d-block elements have partly filled d subshells, high melting points because of strong metallic bonding by unpaired d electrons, and variable oxidation states differing by unity. The ns and (n-1)d energies are close, so both sets of electrons bond. Zn, Cd and Hg have filled d10 and are not typical transition elements.
2. Colour arises from d-d transitions in ions with partly filled d orbitals; d0 and d10 ions (Sc3+, Zn2+, Cu+) are colourless. Magnetic moment is \( \sqrt{n(n+2)} \) B.M. with n unpaired electrons. Transition metals and their compounds are good catalysts because of variable valency and free valencies on the surface, and they form interstitial compounds and alloys.

Oxo Compounds of Chromium and Manganese

1. Potassium dichromate is orange in acid and turns yellow chromate in alkali. In acid it oxidises iodide, Fe2+ and H2S and is reduced to green Cr3+. It is a primary standard because it is not hygroscopic. The blue CrO5 test detects hydrogen peroxide.
2. KMnO4 is reduced to Mn2+ in acid, to MnO2 in neutral or weakly alkaline medium and to green manganate in strong alkali. Fused with KOH it gives green K2MnO4. Sulphuric acid, not HCl, is used for acid medium.

Copper, Silver and Gold

1. Cu+ disproportionates in water because of the large hydration energy of Cu2+. Copper is estimated iodometrically by liberating iodine from iodide. Gold and silver have similar sizes because of the lanthanide contraction.

Lanthanoids

1. The +3 state is common; Ce4+ is oxidising and Eu2+ and Yb2+ are reducing. The lanthanoid contraction is caused by poor shielding by 4f electrons and makes Zr and Hf (and Nb and Ta) almost identical in size. Basicity of the hydroxides decreases from La to Lu.

Actinoids

1. The 5f, 6d and 7s levels are close in energy, so actinoids show a wider range of oxidation states than the lanthanoids, from +3 up to +7 for neptunium and plutonium. Their 5f electrons are less shielded than the 4f electrons, and the elements beyond uranium are transuranic.