1:02 AMThe p-Block Elements
The p-Block Elements
Members: Nitrogen, Phosphorus, Arsenic, Antimony, Bismuth
Electronic configuration: ns2, np3 is the common valence shell electron configuration
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Increasing: Atomic and ionic radii, electro positivity, metallic nature, melting point density
Decreasing: Electro negativity, ionisation energy
Note: The common oxidation state of these elements = -3, +3, +5
In the case of nitrogen all oxidation states from +1 to +4 tend to
disproportionate in acid solution.
Oxide: The members in nitrogen family form two types of oxides E2O3 and E2O5. The oxides in the higher oxidation state of the element are more acidic than that of lower oxidation state.
Dinitrogen – Preparation
In the laboratory, dinitrogen is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.
Due to decay of nitrogenous organic matter ammonia is present in air and soil
Ammonia salt which decomposes when treated with calcium hydroxide gives ammonia.
Optimum conditions for the production of ammonia are the presence of 200 atm pressure, 700 K temperature, and the use of a catalyst such as iron oxide with small amounts of K2O and Al2O3.
Shape of Ammonia – Triagonal Pyramidal structure (refer page 171)
Note: Ammonia solution precipitates the hydroxides of metals from their salt solution
Detection of metal ions by ammonia
Ammonia forms linkages with metal ions and forms complex compounds. This helps in detection of metal ions.
Cu2++4NH3 → [Cu (NH3)4]2+
Ag++Cl- → AgCl+2NH3 → [Ag (NH3)2] Cl
Ag++Cl- = Colourless
[Ag (NH3)2] Cl = Colourless
Ammonia is used for production of fertilisers, nitric acid, liquid ammonia (used as refrigerant)
Heating KNO3 or NaNO3 with con.H2SO4
It is a strong oxidising agent
3Cu+8HNO3 → 3Cu (NO3)2 +2NO+ 4H2O
Cu+ 4HNO3→ Cu (NO3)2 + 3H2O+2NO2
4Zn+ 10HNO3→4Zn (NO3)2+5H2O+N2O
It also oxidises iodine and carbon
Brown Ring Test:
Adding dilute ferrous sulphate solution to an aqueous solution containing nitrate ion, and then adding con.H2SO4 along the sides of the test tube. A brown ring forms between the solution and sulphuric acid layers indicates the presence of nitrate ion.
[Fe (H2O) 6]2++NO→ [Fe (H2O) 5 (NO)] 2++H2O
Note: HNO3, in the gaseous state exists as planar molecule (for structure – refer page 174)
Formation of Fertilizers, T.N.T, Nitro-glycerine, and used as the pickling of stainless steel, etching of metals.
It is a white waxy solid, poisonous, Insoluble in water but soluble in Carbon di Sulphide and glows in dark. One molecule has tetrahedral structure. (For structure refer page 175)
It is obtained by heating white phosphorous at 573K in an inert atmosphere for several days. It possesses iron gray lustre. It is non-poisonous and insoluble in water and CS2. (For structure refer page 176)
α Black Phosphorus– Red phosphorous is heated in a sealed tube at 803K.
β Black Phosphorous- Heating white phosphorous at 473K under high pressure.
It is prepared by the reaction of calcium phosphide with water
Laboratory: It is prepared by heating white phosphorus with con NaOH solution in an inert atmosphere.
Purification of PH3:
Impure PH3 combines with HI to form Phosphonium iodide which on treating with KOH gives phosphine.
It is a colourless gas with rotten fish smell and highly poisonous. It is slightly soluble in water. The PH3 solution decomposes in presence of light giving red phosphorous and H2.
It is absorbed by CuSO4 solution and gives Copper phosphides.
It is technically used in Holme’s signal. And also used in smoke screens.
1. It is prepared by passing dry chlorine over heated white phosphorous.
2. Action of Thionyl Chloride with white phosphorous
Colourless oily liquid
Hydrolysis: In the presence of moisture it gives phosphorous acid and HCl.
Structue: Triagonal pyramidal.
Phosphorous is SP3 hybridised.
Refer page 177 for structure
1. It is prepared by reaction of white phosphorous with excess dry chlorine
2. From SO2Cl2
P4+10 SO2Cl2→4PCl5+10 SO2
Yellowish white powder
Hydrolysis: In moist it gives phosphoric acid
POCl3+3H2O→ H3PO4 + 3HCl
Metals react with PCl5 gives corresponding chlorides. It has trigonal bipyramidal structure. Three equatorial bonds are equivalent. But two axial bonds are longer than equatorial bonds. Bond angles 120 degree and 90 degree.
Note: When PCl5 is heated we get PCl3 and Cl2
PCl5→ PCl3 +Cl2
For Oxoacids of Phosphorous refer page 179 (table 7.5)
Members: Oxygen, Sulphur, Selenium, Tellurium, Polonium
Electronic Configuration: ns2, np4
All the elements form hydrides, type H2E (E= O,S,Se,Te,Po)
The acidic character increases down the group and all the hydrides except H2O posses reducing property.
All the elements form oxides like EO2 and EO3. Both types of oxides are acidic.
Elements of oxygen family forms halides of the type EX6, EX4, EX2
Hexa fluorides have SP3d hybridisation and trigonal bipyramidal structure. Due to the presence of lone pair electrons this shape is also called see saw.
Dimeric halides undergo disproportionation
Note: Down the group acidic character is increases
Oxygen is prepared by decomposition of hydrogen peroxide
When a slow dry stream of oxygen is passed through a silent electrical discharge, conversion of oxygen to ozone occurs. The product is called ozonised oxygen.
It is a pale blue gas, dark blue liquid and violet black solid
Ozone liberates nascent oxygen and it acts as a powerful oxidising agent.
Rhombic sulphur (α- Sulphur):
It is yellow in colour. It is formed by evaporating the solution of roll sulphur in CS2. It is insoluble in water but soluble in CS2 and benzene.
Monoclinic Sulphur (β – Sulphur):
This form of sulphur is prepared by melting rhombic sulphur in a dish and cooling, till crust is formed. Two holes are made in the crust and the remaining liquid poured out. On removing the crust, colour less needle shaped crystals of β – Sulphur are formed. It is stable above 369K. And below 369K it forms Sulphur.
Both rhombic sulphur and mono clinic sulphur have S8 molecules. The shape is called puckered ring. It also kept in cyclo S6, the chair form. At high temperature S2 is the dominant species and is paramagnetic like O2.
Laboratory: Treating a sulphite with dil.H2SO4
Industrially: It is produced as a by-product of the roasting of sulphide ores.
Colourless gas with pungent smell, highly soluble in water
When passed through water, forms a solution of Sulphurous acid.
it reacts with NaOH solution, forming sodium sulphite, which then reacts with more sulphur dioxide to form sodium hydrogen sulphite.
Note: It reacts with chlorine in the presence of charcoal to give sulphuryl chloride.
In refining petroleum and sugar, in bleaching wool and silk, as an anti-chlor
Oxoacids of Sulphur – page 189
Sulphuric Acid – page 189 (contact process)
Properties of Group 15 Elements
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