Ch 4The d- and f-Block Elements — Class 12 Chemistry, concept-first.

The periodic table sets aside two large blocks of elements for atoms whose distinguishing feature is that new electrons enter an inner orbital rather than the outermost shell.

The d-block forms the large middle section of the periodic table. It is sandwiched between the s-block on the left and the p-block on the right.

The outer orbitals of d-block elements generally follow the configuration

The transition elements share a family of characteristic properties that set them apart from the - and -block elements — properties that trace directly back to their partly filled subshell.

Almost every transition element behaves as a classic metal: good tensile strength, ductility, malleability, high thermal and electrical conductivity, and a metallic lustre.

For ions of a given charge within one transition series, radius decreases steadily as atomic number increases.

Ionisation enthalpy rises across each transition series from left to right, because nuclear charge keeps increasing as the inner orbitals are progressively filled.

One of the most distinctive features of the transition elements is the sheer variety of oxidation states they display in their compounds — a range far wider than what is typically seen among -block or…

Forming a divalent metal ion M²⁺(aq) from the solid metal can be broken down into a chain of thermochemical steps: atomisation of the solid into gaseous atoms, successive removal of two electrons (the…

The standard electrode potential for the M³⁺/M²⁺ couple gauges how readily a metal's tripositive ion is reduced to its dipositive ion — equivalently, it measures the relative stability of the +3 state…

Among the stable halides of the 3d metals, the highest oxidation numbers achieved are found in the fluorides: titanium reaches its highest halide as the tetrahalide , while vanadium and chromium go fu…

Transition metals as a class do not behave uniformly toward acids and other oxidising agents. Many of them are sufficiently electropositive to dissolve readily in mineral acids, while a small number a…

When a sample is placed in a magnetic field, it responds in one of a few characteristic ways. A diamagnetic substance is weakly repelled by the applied field, while a paramagnetic substance is attract…

Most ions of the transition series show colour, in sharp contrast to the ions of the s- and p-block. The reason lies in the partly filled d subshell.

A complex (or coordination) compound is one in which a metal ion binds a number of anions or neutral molecules — called ligands — around itself, giving rise to a complex species with its own distinct…

Transition metals and their compounds are widely used as catalysts. This catalytic activity is traced to two abilities that are characteristic of the d-block: the ability to adopt multiple oxidation s…

Interstitial compounds form when small atoms — such as hydrogen, carbon, or nitrogen — become trapped inside the gaps (interstices) of a metal's crystal lattice.

An alloy is a blend of metals, prepared by mixing the molten components together. Many alloys are homogeneous solid solutions, in which the atoms of one metal are distributed randomly among the atoms…

Among the very large number of compounds that the first-row transition metals form, a small set stands out because of its industrial and analytical importance — chiefly the oxides and oxoanions in whi…

Transition-metal oxides are generally formed when the metal reacts with oxygen at high temperature. Every metal of the first transition series except scandium forms an oxide of formula , and these mon…

The -block of the periodic table is made up of two series that sit below the main body of the table: the lanthanoids, the fourteen elements that come right after lanthanum, and the actinoids, the four…

Across the lanthanoid series, the atoms share one common feature: an outer configuration. What changes steadily from one element to the next is how many electrons sit in the level.

Moving across the series from lanthanum to lutetium, both the atomic radii and the ionic radii fall steadily.

Across the lanthanoid series, compounds of lanthanum(III) and of in general are by far the predominant species — the state is the one every member of the series shows reliably.

All the lanthanoids are silvery-white, soft metals, and they tarnish quickly on exposure to air. Softness is not uniform across the series, though — hardness increases with increasing atomic number, a…

The actinoids are the block of fourteen elements that follow actinium, running from thorium (Th, ) to lawrencium (Lr, ).

All the actinoids are taken to share the outer configuration , with the remaining electrons distributed between the and subshells in a variable way.

The trend already familiar from the lanthanoids repeats itself here: moving across the actinoid series, both the atomic size and the size of the ion decrease steadily.

The actinoids display a noticeably wider spread of oxidation states than the lanthanoids do. This is partly explained by the electronic structure of the series: the , , and levels lie close enough in…

The actinoid metals are all silvery in appearance, but unlike the lanthanoids, they display considerable variety in their crystal structures.

The d- and f-block elements are not just of theoretical interest — many of them, and their compounds, are put to everyday industrial, domestic, and technological use.

- Electronic configuration: General valence shell configuration for d-block is ; for f-block, it is . - Transition elements: d-block elements (groups 3–12) are called transition elements because they…

These are the final answers printed at the end of the NCERT chapter. The book gives answers for some intext questions only — every question below links to our complete worked solution.

Higher-order thinking problems from the NCERT Exemplar.

Questions from official CBSE sample papers.