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CHEMISTRY         

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.

 

 

 

 

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

 

 

 

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          

AgCl =White

[Ag (NH₃)₂] Cl = Colourless

Ammonia is used for production of fertilisers, nitric acid, liquid ammonia (used as refrigerant)

 

 

 

 

 

Laboratory preparation:

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

Zn+4HNO₃→Zn (NO₃)₂+2H₂O+4NO₂

It also oxidises iodine and carbon

            I₂+10H₂O→ 2HIO+10NO₂+4H₂O

            C+4HNO₃→CO₂+2H₂O+4NO₂

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.

            NO₃^-+3Fe²⁺+4H⁺→NO+3Fe⁺+2H₂O

            [Fe (H₂O) ₆]²⁺+NO→ [Fe (H₂O) ₅ (NO)] ²⁺+H₂O

                                                            Brown

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.

PHOSPHINE:
Preparation:

It is prepared by the reaction of calcium phosphide with water

          Ca₃P₂+6H₂O→3Ca (OH)₂+2PH₃

Laboratory: It is prepared by heating white phosphorus with con NaOH solution in an inert atmosphere.

            P₄+3NaOH+3H₂O→PH₃+3NaH₂PO₂

Purification of PH₃:

Impure PH₃ combines with HI to form Phosphonium iodide which on treating with KOH gives phosphine.

            PH₄I+KOH→KI+H₂O+PH₃

Properties (Physical):

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.

Chemical Properties:

It is absorbed by CuSO₄ solution and gives Copper phosphides.

            3CuSO₄+2PH₃→Cu₃P₂+3H₂SO₄

Mercuric chloride

3HgCl₂+2PH₃→3Hg₃P₂+6HCl

It is technically used in Holme’s signal. And also used in smoke screens.

 

 

 

 

 

 

 

 

 

Preparation:

1.     It is prepared by passing dry chlorine over heated white phosphorous.

P₄+6Cl₂→ 4PCl₃

2.     Action of Thionyl Chloride with white phosphorous

P₄+8SOCl₂→4PCl₃+4SO₂+2S₂Cl₂

Properties:

Colourless oily liquid

Hydrolysis: In the presence of moisture it gives phosphorous acid and HCl.

                        PCl₃+3H₂O→H₃PO₃+3HCl

Structue: Triagonal pyramidal.

Phosphorous is SP³ hybridised.

Refer page 177 for structure

  Preparation:

1.     It is prepared by reaction of white phosphorous with excess dry chlorine

P₄+10Cl₂→4PCl₅

2.     From SO₂Cl₂

P₄+10 SO₂Cl₂→4PCl₅+10 SO₂

Properties:

Yellowish white powder

Hydrolysis: In moist it gives phosphoric acid

                        PCl₅+H₂O→POCl₃+2HCl

                        POCl₃+3H₂O→ H₃PO₄ + 3HCl

With silver:

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)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

OXYGEN FAMILY

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, EX_4, 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.

2SeCl₂→SeCl₄+3Se

 

 

 

 

Note: Down the group acidic character is increases

Oxygen is prepared by decomposition of hydrogen peroxide

2H₂O₂→2H₂O+O₂

 

 

 

 

    

 

 

 

 

 

Preparation:

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.

                        3O₂→2O₃

Properties:

It is a pale blue gas, dark blue liquid and violet black solid

Chemical Properties:

Ozone liberates nascent oxygen and it acts as a powerful oxidising agent.

                        PbS+4O₃→PbSO₄+4O₂

 

SULPHUR

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.

Laboratory: Treating a sulphite with dil.H₂SO₄

SO₃^2-+2H⁺→H₂O+SO₂

Industrially: It is produced as a by-product of the roasting of sulphide ores.

            4FeS₂+11O₂→2Fe₂O₃+8SO₂

Properties:

Colourless gas with pungent smell, highly soluble in water

When passed through water, forms a solution of Sulphurous acid.
                        SO₂+H₂O→H₂SO₃

With NaOH
it reacts with NaOH solution, forming sodium sulphite, which then reacts with more sulphur dioxide to form sodium hydrogen sulphite.

            2NaOH+SO₂→Na₂SO₃+H₂O

            Na₂SO₃+H₂O+SO₂→2NaHSO₃

Note: It reacts with chlorine in the presence of charcoal to give sulphuryl chloride.

            SO₂+Cl₂→SO₂Cl₂

In refining petroleum and sugar, in bleaching wool and silk, as an anti-chlor

 

Refer

Oxoacids of Sulphur – page 189

Sulphuric Acid – page 189 (contact process)