Ch 14The p-Block Elements — Class 12 Chemistry, concept-first.

Group 15 of the periodic table is headed by nitrogen and continues through phosphorus, arsenic, antimony, bismuth, and the synthetic element moscovium.

Molecular nitrogen, , makes up about 78% of the atmosphere by volume, making it by far the largest reservoir of the element.

Every element of Group 15 carries the same valence-shell electronic configuration, . The subshell is completely filled while the three orbitals each hold exactly one electron, giving a symmetrical, ha…

Both the covalent radius and the ionic radius (measured in a given oxidation state) grow larger on descending Group 15, as expected from the addition of successive electron shells.

Ionisation enthalpy falls steadily on moving down Group 15, a direct consequence of the gradual increase in atomic size, which pulls the outermost electron further from the nucleus and makes it easier…

Electronegativity in Group 15 broadly decreases on going down the group, tracking the steady increase in atomic size — a larger atom holds a shared pair of electrons less tightly.

Every element in Group 15 is polyatomic in its elemental form, but dinitrogen is the odd one out — it exists as the diatomic gas , whereas all the other members of the group are solids at room tempera…

The elements of Group 15 most commonly display the oxidation states , and . Descending the group, size and metallic character both increase, and this steadily weakens the tendency to adopt the state —…

Dinitrogen is manufactured on an industrial scale by liquefying air and then separating it by fractional distillation: liquid nitrogen, which boils at the lower temperature of 77.2 K, distils off firs…

Small amounts of ammonia are present naturally in air and soil, produced by the decay of nitrogen-containing organic matter such as urea:

Nitrogen is unusual in forming a whole family of oxides spanning almost every oxidation state from to .

Nitrogen forms a small family of oxoacids — hyponitrous acid (), nitrous acid (), and nitric acid () — of which nitric acid is by far the most important.

Elemental phosphorus does not exist as a single form — it occurs as several allotropes, of which white, red and black phosphorus are the most important.

Phosphine () is the simplest hydride of phosphorus, and both its preparation and its chemistry closely parallel — while also contrasting with — ammonia.

Beyond its hydride, phosphorus forms an extensive series of halides with the halogens. Two general families exist, distinguished by the oxidation state of phosphorus: the trihalides (formed with all f…

Phosphorus trichloride () is the most important of the phosphorus trihalides.

Phosphorus pentachloride () is the best-known phosphorus pentahalide and an important chlorinating agent in the laboratory.

Phosphorus forms a rich family of oxoacids, summarised in Table 7.5 along with their formulas, oxidation states, characteristic bonds, and how each is prepared.

Moving from Group 15 to the next column of the p-block, Group 16 comprises oxygen, sulphur, selenium, tellurium, polonium and the synthetic element livermorium.

Oxygen is the single most abundant element on Earth. It makes up about 46.6% by mass of the earth's crust, and dry air itself is 20.946% oxygen by volume — the element most of terrestrial chemistry an…

Every element of Group 16 has six electrons in its outermost shell, giving the general valence configuration .

As with every group of the periodic table, moving down Group 16 adds successive electron shells, so both the atomic radius and the ionic radius () increase steadily from oxygen to polonium (see Table…

Ionisation enthalpy decreases down Group 16, the expected consequence of increasing atomic size — the outermost electron sits progressively farther from the nucleus and is easier to remove.

Electron gain enthalpy in Group 16 does not fall into a single simple trend. Oxygen, despite being the most electronegative element in the group, has a less negative electron gain enthalpy than sulphu…

Oxygen has the second-highest electronegativity of any element, exceeded only by fluorine. Moving down Group 16, electronegativity decreases steadily with increasing atomic number, from oxygen through…

The physical properties collected in Table 7.6 reveal a clear metal–nonmetal transition running down Group 16: oxygen and sulphur are non-metals, selenium and tellurium are metalloids, and polonium is…

Group 16 elements display a wide range of oxidation states (Table 7.6). The stability of the state falls steadily down the group, and polonium barely shows it at all.

Dioxygen () is the elemental, molecular form in which oxygen is normally encountered, and it is central both to laboratory chemistry and to industrial gas production.

When oxygen combines with any other element, the resulting binary compound is called an oxide. Because oxygen forms compounds with almost every element in the periodic table, oxides are extremely nume…

Ozone, , is an allotropic form of dioxygen that is far more reactive than and therefore does not persist for long once formed at ground level.

Sulphur exhibits numerous allotropes — different structural forms of the same element — of which the yellow rhombic (-sulphur) and monoclinic (-sulphur) forms are by far the most important.

Burning sulphur in air or oxygen produces sulphur dioxide along with a small amount (6–8%) of sulphur trioxide as a by-product: In the laboratory, is conveniently generated by treating a sulphite salt…

Sulphur forms a remarkably wide range of oxoacids, including (sulphurous acid), (thiosulphuric acid), , , the family (with to ), (sulphuric acid), (pyrosulphuric acid, i.e.

Sulphuric acid ranks among the most important industrial chemicals produced anywhere in the world — a nation's industrial strength is sometimes judged by how much sulphuric acid it manufactures and co…

Group 17 of the periodic table brings together fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine (At) and tennessine (Ts).

Fluorine and chlorine occur fairly abundantly in nature, while bromine and iodine are comparatively scarce.

All noble gases have completely filled valence shells — helium is and every other member has the general configuration (e.g. neon , argon ).

Within their respective periods, the halogens have the smallest atomic radii of any group, a consequence of the maximum effective nuclear charge they experience relative to other elements in the same…

Because the halogens sit only one electron short of a stable noble-gas configuration, they show very little inclination to give up an electron of their own — and this shows up as a very high ionisatio…

Halogens record the most negative electron gain enthalpies of any elements in their respective periods — unsurprising, since accepting one more electron completes their octet and gives them a noble-ga…

Since the noble gases have a complete octet and essentially no tendency to attract a shared pair of electrons, electronegativity is not normally defined for most of them — a value is only meaningful f…

The halogens show textbook-smooth trends in their physical behaviour. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid — and both melting and boiling po…

Every halogen shows the –1 oxidation state, simply by picking up the one electron it needs to complete its octet.

Chlorine was first isolated in 1774 by Scheele, who obtained it by reacting hydrochloric acid with manganese dioxide.

Hydrogen chloride was first prepared by Glauber in 1648, who heated common salt with concentrated sulphuric acid.

Because of its high electronegativity and small atomic size, fluorine forms only a single oxoacid: HOF, known as fluoric(I) acid or hypofluorous acid.

When two different halogens combine directly, they produce an interhalogen compound. Because halogens differ in size and electronegativity, these compounds always pair a larger, more electropositive h…

Group 18 of the periodic table brings together helium, neon, argon, krypton, xenon, radon and oganesson.

With the exception of radon and the synthetic element oganesson, every noble gas occurs naturally in the atmosphere.

Every noble gas except helium shares the same valence-shell pattern, — a completely filled outer and subshell.

Because their electronic configuration is so stable, noble gas atoms hold onto their electrons unusually tightly, giving the group very high ionisation enthalpies — among the highest of any elements i…

Moving down Group 18, from helium to radon, atomic radius increases steadily — visible directly in Table 7.12, where the radius grows from 120 pm for He to 220 pm for Xe.

Since a noble gas atom already has a completely filled, exceptionally stable electronic configuration, it has essentially no inclination to accept an additional electron — doing so would force that ex…

All members of Group 18 exist as single, uncombined atoms (monoatomic gases) rather than as diatomic or polyatomic molecules — a direct consequence of their filled-shell inertness, since there is no d…

Noble gases are, as a rule, the least chemically reactive elements in the periodic table. Two structural reasons explain this inertness: