Group 15 includes Nitrogen, Phosphorus, Arsenic, Antimony and Bismuth.

Among these Nitrogen and Phosphorus are non metals, Arsenic and Antimony are metalloids and Bismuth is a typical metal. Nitrogen is the most abundant element in the atmosphere. Nitrogen is also present in the earth’s crust in the form nitrates. Phosphorus occurs in minerals of the apatite family, which are the main components of phosphate rocks. Phosphorus is an essential constituent of animal and plant matter. It is present in bones as well as in living cells. Phosphoproteins are present in milk and eggs. Arsenic, antimony and bismuth are found mainly as Sulphide minerals.

Valence shell electronic configuration of these elements is ns2 np3. The atomic radii of these elements is in the order Bi>Sb>As>P>N. The ionization enthalpy of group 15 elements is more than that of group 14 because they have half-filled electronic configuration. The order of the ionization enthalpies is N>P>As>Sb>Bi. The order of electronegativity is N>P>As>Sb=Bi. All the elements except Nitrogen exhibit allotropy.

The common oxidation states are -3,+3,+5. The tendency to exhibit -3 oxidation state decreases down the group due to increase in size and metallic character. The stability of +5 oxidation state decreases down the group and that of +3 oxidation state increases down the group. Nitrogen shows +1,+2,+4 and Phosphorus shows +1,+4. Nitrogen has a maximum covalency of 4.

Nitrogen differs from the rest of the members of this group due to its small size, high electronegativity, high ionization enthalpy and non-availability of d orbitals.

Nitrogen has the ability to form pπ-pπ bonds with itself and other elements like Carbon, Oxygen. Nitrogen exists as a diatomic molecule with triple bond whereas P, As, Sb, Bi only form single bonds with themselves.

Hydrides of Group 15 elements:

Stability order: NH3> PH3> AsH3> SbH3> BiH3

NH3 is a mild reducing agent whereas BiH3 is a strong reducing agent

Basicity: NH3 > PH3 > AsH3 > SbH3 > BiH3

Oxides of Group 15 elements:

The form two types of oxides which are X2O3, X205. Oxide (X2O3) of nitrogen and phosphorus are acidic, Arsenic and Antimony are metalloids, Bismuth is basic.

Halides of Group 15 elements:

Group 15 halides form trihalides and pentahalides where pentahalides are more covalent than trihalides. Nitrogen only forms trihalides because of the non-availability of d-orbitals and NF3 is the only stable compound.

Preparation of N2:

Dinitrogen is produced commercially by the liquefaction and fractional distillation of air.

In the laboratory, it is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.

Very pure N2 can be obtained by the thermal decomposition of sodium or barium azide.

The main use of dinitrogen is in the manufacture of ammonia and other industrial chemicals containing nitrogen.

Preparation of NH3:

On a small scale ammonia is obtained from ammonium salts which decompose when treated with caustic soda or calcium hydroxide.

On a large scale, ammonia is manufactured by Haber’s process. N2 (g) + 3H2 (g)→ 2NH3 (g).

Ammonia is a colorless gas with a pungent odor. And is used to produce various nitrogenous fertilizers.

Preparation of HNO3:

In the laboratory, nitric acid is prepared by heating KNO3 or NaNO3 and concentrated H2SO4 in a glass retort.

On a large scale it is prepared mainly by Ostwald’s process.

It is a colorless liquid and is used in the pickling of stainless steel, etching of metals and as an oxidizer in rocket fuels.

Now let us learn about few phosphorous compounds.

Phosphorous is found in different allotropic forms like Red, Black and White phosphorous. White phosphorous is a white translucent solid which is insoluble in h2o but soluble in CS2 and is less stable. Red Phosphorus is obtained by heating white phosphorus at 573K in an inert atmosphere for several days. When red phosphorus is heated under high pressure, a series of phases of black phosphorus is formed.

Black phosphorus has two forms α-black phosphorus and β-black phosphorus. α-Black phosphorus is formed when red phosphorus is heated in a sealed tube at 803K. β-Black phosphorus is prepared by heating white phosphorus at 473 K under high pressure.

Preparation of Phosphine(PH3):

Phosphine is prepared by the reaction of calcium phosphide with water or dilute HCl.

In the laboratory, it is prepared by heating white phosphorus with concentrated NaOH solution in an inert atmosphere of CO2.

It is a colorless gas with rotten fish smell and is highly poisonous and it is mainly used in the Holme’s Signal.

Preparation of PCl3:

It is obtained by passing dry chlorine over heated white phosphorus.

It is also obtained by the action of thionyl chloride (SOCl2) with white phosphorus.

It is a colorless oily liquid and hydrolyses in the presence of moisture. It has sp3 hybridization with pyramidal shape.

Preparation of PCl5:

It is prepared by the reaction of white phosphorus with excess of dry chlorine.

It can also be prepared by the action of SO2Cl2 on phosphorus.

PCl5 is a yellowish white powder and has a trigonal bipyramidal structure in the liquid and gaseous phases whereas in solid state it exists as an ionic solid [PCl4]+ tetrahedral and [PCl6]-