Ch 8Transition and Inner Transition Elements — Class 12 Chemistry, concept-first.

The transition elements belong to the d block of the periodic table. As per the IUPAC convention, a transition metal atom has an incomplete d-subshell, or it gives cations with an incomplete d subshel…

The transition elements are placed in periods 4 to 7 and groups 3 to 12; those constitute the 3d, 4d, 5d and 6d series (Fig. 8.1).

The 3d series begins with Sc (Z = 21) and ends with Zn (Z = 30). Argon, Ar, is the noble gas preceding the 3d series, and its electronic configuration is .

Table 8.2 indicates that the expected electronic configuration of chromium (Z = 24) differs from the observed configuration.

One of the notable features of transition elements is the great variety of oxidation states they show in their compounds.

All transition elements are metals, and show properties that are characteristic of metals. They are hard, lustrous, malleable, ductile, and form alloys with other metals.

Moving across the first transition series, the gradually filling 3d subshell leaves its fingerprints on every measurable atomic property.

Atomic radii of the elements of the transition series decrease gradually from left to right (Fig. 8.3 and Table 8.5).

The ionization enthalpies of transition elements are intermediate between those of s-block and p-block elements.

Low ionisation enthalpies and vacant d orbitals in the outermost shell are responsible for the metallic character of the transition elements.

The compounds of transition metals exhibit magnetic properties due to the unpaired electrons present in their atoms or ions.

A substance appears coloured if it absorbs a portion of visible light. The colour depends upon the wavelength of absorption in the visible region of electromagnetic radiation.

Transition metals and their compounds exhibit good catalytic properties. They have proven to be good homogeneous and heterogeneous catalysts, partly because of their ability to participate in differen…

When small atoms like hydrogen, carbon or nitrogen are trapped in the interstitial spaces within the crystal lattice, the compounds formed are called interstitial compounds.

Transition metals form alloys, where atoms of one metal are distributed randomly in the lattice of another metal. The metals with similar radii and similar properties readily form alloys.

Two compounds dominate the laboratory and industrial chemistry of manganese and chromium: potassium permanganate, , and potassium dichromate, .

(the section title prints "Preparation of potassium permaganate" — the book's own spelling of permanganate; kept verbatim in the heading, spelt correctly in this text)

a. In acidic medium : The oxidizing reactions of in acidic medium

The book lists five uses of potassium permanganate —

In the industrial production, finely powdered chromite ore () is heated with anhydrous sodium carbonate () and a flux of lime in air in a reverbatory furnace.

i. Oxidation of from an aqueous solution of KI by acidified gives . Potassium dichromate is reduced to chromic sulphate. Liberated turns the solution brown.

Physical properties

Most metals are found in the earth's crust in the form of their salts, such as carbonates, sulphates, sulphides and oxides.

Commercial extraction of metals from their ores is called metallurgy. Different methods are used for their extraction, depending on the nature of a metal and its ore.

Iron is extracted from haematite by its reduction using coke and limestone. Carbon in the limestone is reduced to carbon monoxide. Carbon and carbon monoxide together reduce to metallic iron.

Elements whose f orbitals get filled up by electrons are called f block elements. These elements are placed separately at the bottom of the periodic table.

- i. Properties are similar to d block elements - ii. Electrons are added to f subshells of the (n-2) level - iii. Placed between (n-1)d and ns block elements

- i. Soft metals with silvery white colour and moderate densities of ~ 7 g cm⁻³. Colour and brightness reduces on exposure to air - ii. Good conductors of heat and electricity. - iii.

The electronic configuration of lanthanoids is . This is because is the electronic configuration of xenon, and we can simplify the electronic configuration of lanthanoids by writing (the book prints "…

The +3 oxidation state is common to all the elements, in which the 2 electrons of the s- subshell and one from the d or f- subshell are removed.

Some trivalent ions () are coloured, in the solid state as well as in solution. The colour of a lanthanoid ion is due to f-f transitions, which correspond to energy in the visible region of the electr…

As we move along the lanthanoid series, there is a decrease in atomic and ionic radii (Fig. 8.6). This steady decrease in the atomic and ionic radii is called Lanthanoid contraction.

The lanthanoid compounds are present in every household — inside colour television tubes. When electrons are bombarded on certain mixed lanthanoid compounds, they emit visible light over a small wavel…

The last row of elements in the periodic table is the actinoid series. It begins at thorium (Z = 72) and ends at lawrencium (Z = 103).

- i. Similar to lanthanoids, they appear silvery white in colour. - ii. These are highly reactive radioactive elements - iii.

We have seen that the half-lives of natural thorium and uranium isotopes are so long that we get very negligible radiation from these elements. We find them in everyday use.

You have seen that elements with atomic number greater than 92 are called 'Transuranium'. Elements from atomic number 93 to 103 are now included in the actinoid series, and those from 104 to 118 are c…

Sample papers and previous-year board questions for this subject.