Sunday, May 27, 2018

Chemistry: p-Block Elements

Revision Notes on p-Block Elements:

 Boron Family (Group 13 Elements )

  • Members: B, Al, Ga, In & Tl
  • Melting Point: Decreases from B to Ga and then increases up to Tl.
  • Ionization Energies: 1st <<< 2nd < 3rd
  • Metallic Character:  Increases from B to Tl. B is non-metal

Boron

Preparation of Boron:
  • From Boric Acid: B2O3(s) + 3Mg(s) →  2B(s) +3 MgO(s)
  • From Boron Trichloride
    • (at 1270 k): 2BCl3+ 3H2 (g) →  2B(s) + 6HCl (g)
    • (at 900 0C): 2BCl3(g) + 3Zn (s) →  2B(s) + 3 ZnCl2 (s)
  • By electrolysis of fused mixture of boric anhydride (B2O3) and magnesium oxide (MgO) & Magnesium fluoride at 1100 0C
    • 2 MgO- →  2Mg + O2(g)
    • B2O3 + 3Mg →  2B + 3MgO
  • By thermal decomposition of Boron hydrides & halides: B2H(g) + Δ →  2B(s) + 3H(g)

Compounds of Boron:

Orthoboric acid (H3BO3)
Preparation of Orthoboric acid
  • From borax : Na2B4O7 + H2SO4 + 5H2O →  Na2SO4 + 4H3BO3
  • From colemanite Ca2B6O11 + 2SO2 + 11H2O →  2Ca(HSO3)2 + 6H3BO3
Properties of Orthoboric acid
  • Action of Heat:    
  • Weak monobasic acidic behavior:  B(OH)3 ↔ H3BO3 ↔ H+ + H2O +
Thus on titration with NaOH, it gives sodium metaborate salt
H3BO3 + NaOH ↔ NaBO2  + 2H2
  • Reaction with Metaloxide: 
  • Reaction with Ammonium boro fluoride: 
Borax (sodium tetraborate) Na2B4O7. 10H2
Preparation from Boric Acid
4H3BO3 + Na2CO3 --> Na2B4O7 + 6H2O + CO2
Properties of Borax
  • Basic Nature:-
Aqueous solution of borax  is alkaline in nature due to its hydrolysis
Na2B4O7 + 3H2O →  NaBO2 + 3H3BO3
NaBO2 + 2H2O → NaOH + H3BO3
  • Action of heat: 
 
Diborabe( B2H6)
Preparation of Diborane:
Reduction of Boron Trifluoride:
BF3 + 3LiAlH4 →  2B2H6 + 3 LiAl F4
From NaBH4:
2NaBH4 + H2SO  B2H+ 2H+ Na2SO4 2NaBH4 + H3PO→  B2H+ 2H+ NaH2PO4
Properties of Diborane:
  • Reaction with water: B2H6 + H2O -->2H3BO3 + 6H2
  • Combustion: B2H6 +2O2 --? B2O3 + 3H2O  ΔH =  -2615 kJ/mol

Compounds of Aluminium:

Aluminium Oxide or Alumina (Al2O3)
2Al(OH)3 +Heat →   Al2O3 + 2H2O
2Al(SO4)3 +Heat →   Al2O3 + 2SO3
(NH4)2Al2(SO4)3·24H2O --> 2NH3 +Al2O3 + 4SO3 + 25 H2O
Aluminum Chloride AlCl3:
Structure of Aluminium Chloride:
 Aluminium Chloride
Properties of Aluminium Chloride
  • White, hygroscopic solid
  • Sublimes at 183 0C
  • Forms addition compounds with NH3, PH3, COCl2 etc.
  • Hydrolysis: AlCl3 + 3H2O --> Al(OH)3 + 3HCl + 3H2O 
  • Action of Heat: 2AlCl3 .6H2O --> 2Al(OH)3à Al2O3+ 6HCl + 3H2O

Carbon Family (Group 14 Elements):

  • Members: C, Si, Ge, Sn, & Pb
  • Ionization Energies: Decreases from C to Sn and then increases up to Pb.
  • Metallic Character:  C and Si are non metals, Ge is metalloid and Sn and Pb are metals
  • Catenation:  C and Si show a tendency to combine with its own atoms to form long chain polymers

Compounds of Carbon:

Carbon Monoxide
Preparation  of Carbon Monoxide
  • By heating carbon in limited supply of oxygen: C + 1/2O2 --> CO.
  • By heating oxides of heavy metals e.g. iron, zinc etc with carbon.
    • Fe2O3 + 3C →  2Fe + 3CO
    • ZnO + C →  Zn + CO
  • By passing steam over hot coke: C + H2O →  CO + H(water gas)
  • By passing air over hot coke: 2C + O2 + 4N→  2CO + 4N2 (Producer gas)
?Properties of Carbon Monoxide:
  • A powerful reducing agent : Fe2O3 + 3CO →  2Fe + 3CO2 CuO + CO →  Cu + CO2
  • Burns in air to give heat and carbon dioxide: CO + 1/2O2 →  CO2 + heat.
Tests For Carbon Monoxide:
  • Burns with blue flame
  • Turns the filter paper soaked in platinum or palladium chloride to pink or green.
Carbon di-oxide
Preparation of Carbon di-oxide
  • By action of acids on carbonates: CaCO3+ 2HCl →  CaCl2 + H2O + CO2
  • By combustion of carbon: C + O2 →  CO2
Properties of Carbon di-oxide
  • It turns lime water milky Ca(OH)2 + CO2→  CaCO3 ¯ + H2O,
  • Milkiness disappears when CO2 is passed in excess CaCO3 + H2O + CO2 →  Ca(HCO3)2
  • Solid carbon dioxide or dry ice is obtained by cooling CO2 under pressure. It passes from the soild state straight to gaseous state without liquefying (hence dry ice).
Carbides:
  • Salt like Carbides : These are the ionic salts containing either C22- (acetylide ion) or C4- (methanide ion)e.g. CaC2, Al4C3, Be2C.
  • Covalent Carbides : These are the carbides of non-metals such as silicon and boron. In such carbides, the atoms of two elements are bonded to each other through covalent bonds. SiC also known as Carborundum.
  • Interstitial Carbides : They are formed by transition elements and consist of metallic lattices with carbon atoms in the interstices. e.g. tungsten carbide WC, vanadium  carbide VC.

Compounds of Silicon:

Sodium Silicate (Na2SiO3):
?Prepared by fusing soda ash with pure sand at high temperature: Na2CO3+ SiO3 →  Na2SiO3 +CO2
Silicones:  Silicon polymers containing Si – O – Si linkages formed by the hydrolysis of alkyl or aryl substituted chlorosilanes and their subsequent polymerisation.
Silicates:
Salts of silicic acid, H4SiO4 comprised of SiO44- units having tetrahedral structure formed as result of sp3 hybridization.

Nitrogen Family (Group 15 Elements)

  • Members: N, P, As, Sb & Bi
  • Atomic Radii: Increases down the group. Only a small increases from As to Bi.
  • Oxidation state: +3, +4 & +5.Stability of +3 oxidation state increases down the group.
  • Ionization energy: Increases from N to Bi.

Nitrogen

Preparation of Nitrogen:
  • 3CuO + 2NH3 + Heat --> N2 + Cu + 3H2O
  • CaOCl+ 2NH3 + Heat --> CaCl2+ 3H2O + N2
  • NH4NO2 +Heat --> 3H2O + N+Cr2O3
 Properties of Dinitrogen:
  • Formation of Nitrides (with Li, Mg, Ca & Al):  Ca + N2 +Heat →  Ca3N2
  • Oxidation: N2 + O  2NO
  • Reaction with carbide (at 1273 K): CaC2 + N2 →  CaCN2 + C

Oxides of Nitrogen


Oxy -Acids of Nitrogen :

Oxy Acids
Name of oxy – acid
1.   H2N2O2
Hyponitrous acid
2.   H2 NO2
Hydronitrous acid
3.   HNO2
Nitrous acid
4.   HNO3
Nitric acid
5.   HNO4
Per nitric acid

Ammonia (NH3):

Preparation of Ammonia:
  • By heating an ammonium salt with a strong alkali ;NH4Cl + NaOH --> NH3­ + NaCl + H2O
  • By the hydrolysis of magnesium nitride: Mg3N2 + 6H2O --> 3Mg(OH)2 + 2NH3.
  • Haber's process :  N2(g) + 3H2(g) --> 2NH3(g).
Properties of Ammonia:
  • Basic nature : Its aq. solution is basic in nature and turns red litmus blue. NH3 + H2O  ↔  NH4+ + OH-
  • Reaction with halogens :
    • 8NH3 + 3Cl2 --> 6NH4Cl + N2
    • NH3 + 3Cl2 (in excess) → NCl3 + 3HCl
    • 8NH3 + 3Br→  6NH4Br + N2
    •  NH3 + 3Br(in excess) →  NBr3 + 3HBr
    • 2NH3 + 3I2 →  NH3.NI3 + 3HI
    • 8NH3.NI3 →  6NH4I + 9I2 + 6N2
  • Complex formation :
    • Ag+ + NH3 →  [Ag(NH3)2]+
    • Cu2+ + 4NH3  [Cu(NH3)4]2+
    • Cd2+ + 4NH3  [Cd(NH3)4]2+
Precipitation of heavy metal ions from the aq. solution of their salts :
  •  FeCl3 + 3NH4OH →  Fe(OH)3 + 3NH4Cl                               Brown ppt.
  • AlCl3 + 3NH4OH →  Al(OH)3 + 3NH4Cl                      White ppt.
  • CrCl3 + 3NH4OH →  Cr(OH)3 + 3NH4Cl                               Green ppt.

Phosphorus:

Allotropy of Phosphorus:
a) White phosphorus: 
White phosphorus
  • Translucent white waxy solid
  • Extremely reactive
  • Poisonous and insoluble in water
b) Red Phosphorus:
  • Formed by heating white phosphorus in absence of air.
  • Does not burn spontaneously at room temperature. Red Phosphorus
c) Black Phosphorus:  Formed by further heating of red phosphorus. 
Compounds of Phosphorus:
a) Phosphine, PH3:
Preparation of Phosphine
  • Ca3P2 + 6H2O →  2 PH3 + 3 Ca(OH)2
  • 4H3PO3 +Heat →  PH3+ 3 H3PO4
  • PH4I +KOH →  PH3+KI + H2O
  • P4 + 3KOH + 3H2O →  PH3 +3KH3PO2
Properties of Phosphine:
  • Formation of Phosphonic Iodide: PH+ HI  à PH4I
  • Combustion: PH+ 2O2  à H3PO4
b) Phosphorous Halides:
Preparation:
  • P4+ 6Cl→  4PCl3
  • P4+ 10Cl2 →  4PCl5
  • P4+ 8SOCl2 →  4PCl3 + 4SO2+ 2S2Cl2
  • P4+ 10SOCl2 →  4PCl5 + 10SO2
Properties:
  • PCl3 + 3H2O → H3PO3 + 3HCl
  • PCl5 + 4H2O →  POCl3 à H3PO4 +5HCl
  • PCl3 + 3CH3COOH →  3 CH3COCl +H3PO3
  • PCl5 + CH3COOH →   CH3COCl + POCl3+ HCl
  • 2Ag + PCl5  →  2AgCl + PCl3
  • 2Sn + PCl5 → SnCl4 + 2PCl3
  • PCl5 + Heat →  PCl3 + Cl2
?C) Oxides of Phosphorus:
Oxides of Phosphorus
d) Oxy – Acids of Phosphorus:
Oxo acid
Name 
      H3PO2
Hypophosphorus acid
      H3PO3
Phosphorus acid
      H4P2O6
Hypophosphoric acid
      H3PO4
Orthophosphoric acid
      H4P2O7
Pyrophosphoric acid
      HPO3
Metaphosphoric acid

Oxygen Family (Group 16 Elements) :

Sr. No.
Property
Oxygen
Sulfur
Selenium
Tellurium
Polonium
1.
Configuration
[He]2s22p4
[Ne]3s23p4
[Ar]4s24p4
[Kr]5s25p4
[Xe]6s26p4
2.
Common oxidation state
-2
-2, +4, +6
+4, +6
+4, +6

3.
Atomic radius (pm)
66
104
116
143
167
4.
First ionization energy (KJ/mol)
1314
1000
941
869
812
5.
Electronegativity
3.5
2.5
2.4
2.1
2.0

Chemical Properties of Group 16:

Formation of volatile Hydrides:
            
 Formation of Halides:
Formation of Oxide:
a) All elements (except Se) forms monoxide.
b) All elements form dioxide with formula MO2, SO2 is a gas, SeO2 is volatile solid. While TeO2 and PoO2 are non – volatile crystalline solids.
c) Ozone: It is unstable and easily decomposes into oxygen. It acts as a strong oxidising agent due to the case with which it can liberate nascent oxygen.
Oxyacids:
    Sulphur
    Selenium
    Tellurium
    Sulphurous acid H2SO3.
    Sulphuric acid H2SO4
    Peroxomonosulphuric acid H2SO5(Caro’s acid)
    Peroxodisulphuric acid
    H2S2O8 (Marshell’s acid)
    Thio sulphuric acid H2S2O3
    Dithiconic acid H2S2O6
    Pyrosulphuric acid H2S2O7
    Selenious acid H2SeO3
    Selnenic acid H2SeO4
    Tellurous acid H2TeO3.
    Telluric acid H2TeO4.

    Allotropes of Sulphur :

    Rhombic sulphur:
    • It has bright yellow colour.
    • It is insoluble in water and carbon disulphide. Its density is 2.07 gm cm-3and exists as S8 molecules. The 8 sulphur atoms in S8­ molecule forms a puckered ring.
    Monoclinic Sulphur :
    • Stable only above 369 K. It is dull yellow coloured solid, also called b - sulphur. It is soluble in CS2 but insoluble in H2O.
    • It slowly changes into rhombic sulphur. It also exist as S8 molecules which have puckered ring structure. It however, differs from the rhombic sulphur in the symmetry of the crystals
    Plastic Sulphur: 
      • It is obtained by pouring molten sulphur to cold water.
      • It is amorphous form of sulphur.
      • It is insoluble in water as well as CS2.

      Sulphuric Acid:

      •  Due to strong affinity for water, H2SO4 acts as a powerful dehydrating agent. 
      • Concentrated H2SO4 reacts with sugar, wood, paper etc to form black mass of carbon. This phenomenon is called charring.
      • It is moderately strong oxidizing agent. 
      • Decomposes carbonates, bicarbonates, sulphides, sulphites, thiosulphates and nitrites at room temperatures.
      • Salts like chlorides, fluorides, nitrates, acetates, oxalates are decomposed by hot conc. H2SO4 liberating their corresponding acids. ?

      Halogen Family ( Group 17 Elements)

      Inter halogen compounds:
        Type XX’1 (n = 1) (with linear shape)
        Type XX’3 (n = 3) (with T-shape)
        XX’5 (n = 5) (with square pyramidal shape)
        XX’7 (n = 7) with pentagonal bipyramidal shape)
        CIF
        ClF3
        ClF5

        BrF BrCl
        BrF3
        BrF5

        ICl, IBr, IF
        ICl3, IF3
        IF5
        IF7
        Hydrogen Halides:
        Properties of Hydrogen Halides:
        • All the three acids are reducing agents  HCl is not attacked by H2SO4.
          • 2HBr + H2SO4 →  2H2O + SO2 + Br2 ­
          • 2HI + H2SO4   2H2O + SO2 + I2
        • All the three react with KMnO4 and K2Cr2O7
          • 2KMnO4 + 16HCl  2KCl + 2MnCl2 + 8H2O + 5Cl2
          •  K2Cr2O7 + 14HBr  2KBr + 2CrBr3 + 7H2O + 3Br2­
        • Other reactions are similar.
          • Dipole moment : HI < HBr < HCl < HF
          • Bond length: HF < HCl < HBr < HI
          • Bond strength: HI < HBr < HCl < HF
          • Thermal stability: HI < HBr < HCl < HF
          • Acid strength: HF < HCl < HBr < BI
          • Reducing power: HF < HCl < HBr < HI
        Pseudohalide ions and pseudohalogens:
        Ions which consist of two or more atoms of which at least one is nitrogen and have properties similar to those of halide ions are called pseudohalide ions. Some of these pseudohalide ions can be oxidised to form covalent dimers comparable to halogens (X­2). Such covalent dimers of pseudohalide ions are called pseudohalogens.
        The best known psuedohalide ion is CN
        Pseudohalide ions     
        Name
        CN
        Cyanide ion   
        OCN
        Cyanate ion  
        SCN
        Thiocyante ion
        SeCN
        Selenocyanate ion
        NCN2– 
        Cyanamide ion
        N3– 
        Azide ion
        OMC 
        Fulminate ion
        Pseudohalogen
        • (CN)2 cyanogen
        • (SCM)2 thiocyanogen
        Some important stable compound of Xenon
        • XeO3            Pyramidal
        • XeO4            Tetrahedral
        • XeOF4          Square pyramidal
        • XeO2F2           Distorted octahedral
        First rare gas compound discovered was Xe+(PtF6] by Bartlett.
        Oxyacids of Chlorine
          Formula
          Name
          Corresponding Salt
          HOCl
                  Hypochlorous acid
          Hypochlorites
          HClO2
                  Chlorous acid
          Chlorites
          HClO3
                  Chloric acid
          Chlorates
          HClO4
                  Perchloric acid
          Perchlorates
          Acidic Character: Acidic character of the same halogen increases with the increase  in oxidation number of the halogen: HClO4> HClO3 > HClO2 > HOCl
          Preparation
          HOCl :     
          • Ca(OCl)2 + 2HNO3 →  Ca(NO3)2 + 2HOCl
          HClO2 :    
          • BaO2 + 2ClO2 →  Ba(ClO2)2 (liquid) + O2
          • Ba(ClO2)2 + H2SO4(dil.) →  BaSO4 ¯ + 2HClO2
          HClO3 :    
          • 6Ba(OH)2 + 6Cl2 →  5BaCl2 + Ba(ClO3)2 + 6H2O
          • Ba(ClO3)2 + H2SO4(dil.) →  BaSO4 ¯ + 2HClO3
          HClO4 :    
          • KClO4 + H2SO4 →  KHSO4 + HClO4
          • 3HClO3 →  HClO4 + 2ClO2 + H2O

          The Noble Gases (Group 18 Elements):

          The noble gases are inert in nature. They do not participate in the reactions easily because they have
          • stable electronic configuration i.e. complete octet.
          • high ionization energies.
          • low electron affinity.
          Compounds of Xenon
          Molecule
          Total electron pairs (BP + LP)
          Hybridisation
          Shape
          XeF2
          5
          Sp3d
          Linear
          XeF4
          6
          Sp3d2
          Square planar
          XeF6
          7
          sp3d3
          Distorted octahedral

          Uses of Nobles gas

          The noble gases are used in following ways:
          (A) Helium
          • It is used to fill airships and observation balloons.
          • In the oxygen mixture of deep sea divers.
          • In treatment of asthma.
          • Used in inflating aeroplane tyres.
          • Used to provide inert atmosphere in melting and welding of easily oxidizable metals.
          (B)  Neon
          • It is used for filling discharge tubes, which have different characteristic colours and are used in advertising purposes.
          • Also used in beacon lights for safety of air navigators as the light possesses fog and stram perpetrating power.
          (C)  Argon
          Along with nitrogen it is used in gas – filled electric lamps because argon is more inert than nitrogen.

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