Ch 3p-Block Elements-II — Class 12 Chemistry, concept-first.

The previous unit covered the general characteristics of the p-block and its first two groups -- the icosagens (boron family, Group 13) and the tetragens (carbon family, Group 14).

We begin with Group 15, the nitrogen family, comprising nitrogen, phosphorus, arsenic, antimony and bismuth.

About 78% of the earth's atmosphere by volume is dinitrogen (N2) gas, making nitrogen the most abundant element of Group 15 by far.

Down Group 15 from nitrogen to bismuth, the physical state changes from a diatomic gas (N2) to solids, atomic number and atomic mass rise steadily, and atomic radius increases from about 1.55 Å for ni…

Preparation: Nitrogen, being the principal component of air (78% by volume), is obtained industrially on a large scale by the fractional distillation of liquefied air (nitrogen, boiling at 77 K, disti…

Preparation: Ammonia is produced in the body/agriculturally by the hydrolysis (in effect, bacterial or thermal decomposition) of urea: NH2CONH2 + H2O - 2NH3 + CO2.

Laboratory preparation: Nitric acid is prepared in the laboratory by gently heating equal amounts of potassium or sodium nitrate with concentrated sulphuric acid: KNO3 + H2SO4 - KHSO4 + HNO3.

Nitrogen forms a remarkably complete series of oxides spanning every oxidation state from +1 to +5, each with characteristic physical properties and a distinct preparation.

Phosphorus exhibits several allotropic forms, of which the three most common are white (yellow) phosphorus, red phosphorus and black phosphorus, along with less common scarlet and violet forms.

Phosphorus is a highly reactive element, and its most important chemical properties are as follows. Reaction with oxygen: yellow (white) phosphorus catches fire readily in air, giving dense white fume…

Phosphine (PH3) is the most important hydride of phosphorus.

Phosphorous trichloride (PCl3):

Phosphorus forms an important series of oxides — principally phosphorus trioxide (P4O6) and phosphorus pentoxide (P4O10) — built on the same P4 tetrahedral framework as elemental white phosphorus.

The second remaining p-block group is Group 16, the oxygen family or chalcogens ("ore-formers"), so called because most naturally occurring ores are oxides or sulphides of other elements.

Sulphur exists in both crystalline and amorphous allotropic forms. The crystalline forms are rhombic sulphur (also called alpha-sulphur) and monoclinic sulphur (also called beta-sulphur); the amorphou…

Preparation: Sulphur dioxide can be obtained on a large industrial scale by burning elemental sulphur in air, where about 6-8% is further oxidised to sulphur trioxide (S + O2 - SO2; 2S + 3O2 - 2SO3).

Preparation — the Contact process: sulphuric acid can be manufactured by the lead-chamber process, the cascade process or the contact process; the contact process, described here, is the modern indust…

Group 17, the halogen family, comprises fluorine, chlorine, bromine, iodine and the rare radioactive astatine.

Occurrence: the halogens, being highly reactive, are found only in combined form. Fluorine's principal source is fluorspar (fluorite, CaF2), with cryolite and fluorapatite as other ores; chlorine's ma…

Laboratory preparation: hydrochloric acid is prepared by the action of sodium chloride on concentrated sulphuric acid (NaCl + H2SO4 - NaHSO4 + HCl at moderate temperature, and NaHSO4 + NaCl - Na2SO4 +…

Preparation of the hydrogen halides: direct combination of hydrogen with a halogen is a general (though not always practical) route: hydrogen and fluorine react explosively/violently, while hydrogen w…

Each halogen can combine with a different halogen to form a series of binary compounds called interhalogen compounds, generally written AB, AB3, AB5 or AB7, in which the less electronegative (generall…

Fluorine reacts readily and directly with oxygen (unlike the other halogens) to give oxygen fluorides rather than true "oxides" in the conventional sense, since in these compounds fluorine, being more…

Chlorine is the only halogen to form the complete series of four types of oxoacid — hypochlorous acid (HOCl), chlorous acid (HClO2), chloric acid (HClO3) and perchloric acid (HClO4) — spanning oxidati…

Group 18, the noble (inert) gases, comprises helium, neon, argon, krypton, xenon and radon. Because every member has a completely filled outermost electron shell (ns2 np6, except helium which has just…

Occurrence: all the noble gases occur naturally in the atmosphere, generally as trace constituents (with the exception of argon, which at about 0.93% by volume is by far the most abundant of them and…

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