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The p-Block Elements
CHEMISTRY         
The p-Block Elements
Nitrogen Family
Members: Nitrogen, Phosphorus, Arsenic, Antimony, Bismuth
Electronic configuration: ns2, np3 is the common valence shell electron configuration
Group Trend
Top to Bottom
Increasing: Atomic and ionic radii, electro positivity, metallic nature, melting point density
Decreasing: Electro negativity, ionisation energy
Rounded Rectangle: • Nitrogen is Gas. But other elements in the group are solids. Why?
An: Nitrogen is diatomic. But other elements are poly atomic. 
 
 
 
 

 

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.
Rounded Rectangle: • Nitrogen acts as an inert gas. Why?
An: Nitrogen has the ability to form P∏-P∏ multiple bond. So there is a triple bond kept between two nitrogen atoms in nitrogen molecule. 
 
 
 

 

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.
Rounded Rectangle: • Nitrogen not forms pentahalides. Why?
An: Due to non availability of the d orbital in its valance shell. 
 
 
 

 

Dinitrogen – Preparation
In the laboratory, dinitrogen is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.  
Ammonia
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.
 
Haber process
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.
Rounded Rectangle: • In the solid and liquid state ammonia shows high melting and boiling point. Why?
An: Ammonia molecules associated through Hydrogen Bonds. 
 
 
 
 

 

Shape of Ammonia – Triagonal Pyramidal structure (refer page 171)
Note: Ammonia solution precipitates the hydroxides of metals from their salt solution
Rounded Rectangle: • Ammonia acts as Lewis Base. Why?
An: Due to the presence of lone pair electrons in nitrogen atom.  
 
 

 

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          
AgCl =White
[Ag (NH3)2] Cl = Colourless
USES:
Ammonia is used for production of fertilisers, nitric acid, liquid ammonia (used as refrigerant)
Oxides Of Nitrogen
Refer – page 172 and 173 ( table 7.3 and 7.4)
Rounded Rectangle: • Why Does NO2 dimerise?
An: NO2 contains odd number of valence electrons. On dimerisation it is converted to stable N2O4 molecule with even number of electrons.
 
 
 
 
 
Nitric Acid:
Laboratory preparation:
Heating KNO3 or NaNO3 with con.H2SO4
 
Chemical Properties:
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)
USES:
Formation of Fertilizers, T.N.T, Nitro-glycerine, and used as the pickling of stainless steel, etching of metals.
PHOSPHOROUS
Allotropic forms
White phosphorous:
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)
Red phosphorous:
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)
Black Phosphorous:
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
USES:
It is technically used in Holme’s signal. And also used in smoke screens.
Rounded Rectangle: • Prove that PH3 is basic in nature.
An: PH3 reacts with acids like HI to form PH4I
 PH3+HI→PH4I (Phosphonium Iodide) 

 

 
 
 
Rounded Rectangle: • Bond angle of PH4+ is higher than that of PH3. Why?
An: In PH3 one lone pair is exist. But in PH4+ ion there is no lone pair exists.  
 
 
 
 

 

Phosphorous trichloride:
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
Phosphorous Pentachloride:
  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
Rounded Rectangle: • What happens when H3PO3 is heated?
An: On heating it disproportionate to give phosphoric acid and phosphine.                        PCl5→ PCl3 +Cl2
 
 
 
 
Rounded Rectangle: • H3PO3 is dibasic and H3PO4 is tribasic. Why?
An: H3PO3 has two P-OH bonds and H3PO4 has three P-OH bonds. 
 
 

 

For Oxoacids of Phosphorous refer page 179 (table 7.5)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
OXYGEN FAMILY
Members: Oxygen, Sulphur, Selenium, Tellurium, Polonium
Electronic Configuration: ns2, np4
       
  Rounded Rectangle: • The ionisation energy of oxygen family is less than of group 15. Why?
An: Group 15 elements have extra stable half filled P-orbital
 
  Rounded Rectangle: • The large difference between the melting and boiling points of oxygen and sulphur is due to? 
An: Oxygen exists as diatomic molecule but sulphur is poly atomic
 
    Rounded Rectangle: • H2O is liquid but H2S is gas. Why?
An: Due to small atomic size and high electro negativity of oxygen, presence of strong hydrogen bond in oxygen. But it is not found in H2S.
 
 
 
 
 
 
 
 
 
 
 
 
 

 

Hydrides:
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.
Oxides:
All the elements form oxides like EO2 and EO3. Both types of oxides are acidic.
Halides:
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
2SeCl2→SeCl4+3Se
Rounded Rectangle: • H2S is less acidic than H2Te. Why?
An: Due to the decrease in bond (E-H) dissociation energy. 
 
 
 

 

Note: Down the group acidic character is increases
Oxygen:
Oxygen is prepared by decomposition of hydrogen peroxide
Rounded Rectangle: • What is an acidic oxide?
An: the oxides that combines with water to give an acid.
Eg: SO2, CO22H2O2→2H2O+O2
 
 
 
Rounded Rectangle: • What is a basic oxide?
An: the oxide which gives a base with water.
Eg: CaO, BaO 

 

Rounded Rectangle: • Prove that Al2O3 is amphoteric.
An: Al2O3+6HCl+9H2O→2 [Al (H2o) 6]3+ + 6Cl-
 Al2O3+6NaOH+3H2O→2Na3 [Al (OH) 6]    
 
 
 
 
 
Ozone:
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
Allotropic forms:
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.
Sulphur Dioxide
Preparations:
Laboratory: Treating a sulphite with dil.H2SO4
SO32-+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
USES:
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)
 
 
 

Properties of Group 15 Elements

Element/Symbol
Atomic Number
Mass
Electron Configuration
Covalent Radius (pm)
Electronegativity
First Ionizaton Energy (kJ/mol)
Common Physical Form(s)
Nitrogen (N)
7
14.01
1s2 2s2 2p3
75
3.0
1402
Colorless Gas
Phosphorus (P)
15
30.97
[Ne]3s2 3p3
110
2.1
1012
White Solid / Red Solid
Arsenic (As)
33
74.92
[Ar] 3d10 4s2 4p3
121
2.0
947
Yellow Solid / Gray Solid
Antimony (Sb)
51
121.76
[Kr] 4d10 5s2 5p3
140
1.9
834
Yellow Solid / Silver-White Metallic Solid
Bismuth (Bi)
83
208.98
 [Xe] 4f14 5d10 6s2 6p3
155
1.9
703
Pink-White Metallic Solid
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