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p-block elements

p-block elements. Grade 12. Nitrogen Family. Electronic configuration- ns 2 np 3 Atomic and ionic radii- Increases as we move down the group. But there is small increase in the size from As to Bi due to completely filled d- and f- orbitals.

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p-block elements

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  1. p-block elements Grade 12

  2. Nitrogen Family • Electronic configuration- ns2np3 • Atomic and ionic radii- Increases as we move down the group. But there is small increase in the size from As to Bi due to completely filled d- and f- orbitals. Q. Atomic radius of elements increases in a group, but there is only a small increase from As to Bi. A. This is due to the presence of completely filled d-orbitals and/or f-orbitals in them, which have weak screening effect and more effective nuclear charge called as inert- pair effect. • Ionization Enthalpy- Decreases down the group. Q. I.E. of Group 15 elements is much greater than that of the Group 14 and Group 16 elements in the corresponding periods. A. Because of the extra stability of a half-filled p-orbital configuration. • Electronegativity- Decreases down the group.

  3. Chemical Properties • Oxidation States and Trends in Chemical Reactivity- • Common oxidation states are -3,+3 and +5. Q. Nitrogen does not exhibit covalency greater than 4. A. Due to the absence of d-orbitals in the valence shell of N. 2. Tendency to exhibit -3 oxidation state decreases down the group due to increase in size and metallic character.

  4. The stability of +5 oxidation state decreases down the group but stability of +3 oxidation state increases due to inert pair effect. Q. The stability of +5 state decreases and that of +3 state increases down the group. A. Due to inert pair effect. (explain inert pair effect) Q. Metallic character increases down the group. A. Due to decrease in I.E. and increase in atomic size.

  5. Anomalous properties of Nitrogen • Nitrogen has small size, high electronegativity,high IP and non-availability of d-orbitals. • Form p-p pie bonds with itself. • Nitrogen exists as diatomic with one triple bond. Q. Nitrogen exists as diatomic molecule N2 gas at room tempertaure. A. Due to the ability of the N atom to form pπ-pπ triple bond with another N atom. • Bond enthalpy is very high. • P-P, As-As, Sb-Sb have single bonds whereas Bi forms metallic bond.

  6. Q. Nitrogen shows anomalous properties. A. Due to its small size, high electronegativity, high I.E., non-availability of d-orbitals in its valence shell and its ability to form pπ-pπ multiple bonds with itself, and with other elements like C and O.

  7. Weak catenation tendency. Q. Tendency for catenation is less in N as compared to the other members of the group. A. N-N single bond is weaker than those of the other elements. This is due to the high inter-electronic repulsion of the non-bonding electrons, owing to the small N-N bond length. • Non-availability of d- orbitals. • Reactivity towards hydrogen-All elements form hydrides of EH3 type. Stability of Hydrides decreases from NH3 to BiH3, while the reducing character increases. Basicity trend: NH3>PH3>AsH3>SbH3>BiH3 Q. Thermal stability of hydrides decreases from NH3 to BiH3. • E-H bond enthalpy (bond strength) decreases down the group. (E  Group 15 element) Q. Reducing character of EH3 increases from NH3 to BiH3. A. E-H bond strength decreases, so H is easily supplied for reduction, on moving down the group.

  8. Q. Basic character decreases down the group for EH3. A. Due to the presence of a lone pair of electrons on the central atom, they behave as Lewis bases. N being the smallest in size, electron-density on N is high. Thus, it is the strongest base. Base strength decreases with increase in the size of the central atom. Q. NH3 is a stronger base than PH3. (phosphine). A. Due to smaller size of N, electron-density on N is higher. Thus, it is a strong Lewis base. Q. NH3 has exceptionally high b.p. A. Due to the high electronegativity of N, intermolecular H bonds exist between NH3 molecules.

  9. Q. Among hydrides of Group 15 elements, BiH3 is the strongest reducing agent. A. BiH3 is the least stable, because Bi-H bond is the weakest (least bond enthalpy) compared to the E-H bond of the other elements of the group. Q. NH3 molecule is triagonal pyramidal in shape. A. Due to the presence of 3 bp and 1 lp of electrons on the central N atom in the molecule.Structure. Q. NH3 is used in the detection of metal ions such as Cu2+, Ag+ etc. A. Due to the presence of a lone pair on the central N atom, NH3 is a Lewis base. Thus, it donates electron pairs to metal ions and hence forms coloured complexes which help in the detection of metal ions. e.g Cu2+(aq) + 4 NH3 → [Cu(NH3)4]2+(aq) deep blue solution

  10. 2. Reactivity towards oxygen- • Two types of oxides : E2O3 and E2O5 type. • The oxide in higher oxidation state are more acidic than the lower ones. Acidic character decreases down the group.N2O3 and P2O3 are acidic,As2O3 and Sb2O3 are amphoteric and Bi2O3 are basic.

  11. 3. Reactivity towards halogens- Two types-EX3 and EX5.Nitrogen do not form pentahalides due to the non-availability of d-orbitals. Pentahalides are more covalent than trihalides. Q. PCl5 exists, but NCl5 does not. A. Due to the absence of d-orbitals in the valence shell of N,N cannot expand its valence shell. Q. Pentahalides of Group 15 elements are more covalent than trihalides. A. Higher the positive oxidation state of the central atom, the more is its polarizing power and, therefore, more the covalent nature of the bond. 4. Reactivity towards metals- Form binary compounds exhibiting -3 oxidation states.e.g. Calcium nitride, Calcium phosphide etc.

  12. Dinitrogen Preparation- • In the laboratory, nitrogen is prepared by heating a mixture of ammonium chloride and sodium nitrite and a small quantity of water. If ammonium nitrite is heated by itself it decomposes to produce nitrogen gas. However, this reaction is very fast and may prove to be explosive.

  13. By thermal decomposition of ammonium dichromate- (NH4)2Cr2O7 N2+4H2O+Cr2O3 3.By thermal decomposition of sodium or barium azide- Ba(N3)2 Ba+3N2

  14. Properties of Dinitrogen • Dinitrogen is inert at room temperature due to the high bond enthalpy of N-N triple bond. Q. N2 gas is chemically inert at room temperature. A. Due to very high bond enthalpy of N≡N. 2. At high temperature reactivity increases and nitrogen form ionic nitrides with metals and covalent nitrides with non-metals. 6Li+N2 2Li3N

  15. 3Mg+N2 Mg3N2 • It reacts with hydrogen at 773 K in the presence of catalyst forms ammonia (Haber`s Process). N2+3H2 2NH3 • It reacts with dioxygen at very high temperature and forms nitric oxide NO. N2+O2 2NO

  16. Ammonia Preparation- • By decay of nitrogenous organic matter- NH2CONH2+2H2O (NH4)2CO3 2NH3+CO2

  17. On small scale ammonia can be obtained by decomposition of ammonium salts with caustic soda or lime. NH4Cl+Ca(OH)2 NH3+H2O+CaCl2 • On large scale ammonia can be manufactured by Haber`s process. N2+3H2 2NH3

  18. Properties of ammonia • Has high melting and boiling point due to H2 bonding. • Trigonal pyramidal in shape. • Ammonia is highly soluble in water.Its aqueous solution gives OH- in aqueous solution. NH3+H2O NH4+OH- 4. As a weak base, it precipitates the hydroxides of many metals from their salt solutions.

  19. 2FeCl3+3NH4OH Fe2O3.H2O+3NH4Cl (brown ppt.) 5. Acts as Lewis base due to the presence of lone pair of electron on N2.e.g. Cu+2+4NH3 [Cu(NH3)4] +2 (deep blue)

  20. Oxides of NitrogenN2O IUPAC name Dinitrogen monoxide Other name Laughing gas Structure- NH4NO3 (s) → 2 H2O (g) + N2O (g)

  21. NO • Preparation- 2 NaNO2+2 FeSO4+3 H2SO4 → Fe2(SO4)3+2 NaHSO4 + 2 H2O + 2 NOPreferred IUPAC nameNitric oxide Systematic nameNitrogen monoxide Other names Nitrogen(II) oxide

  22. N2O3 • Dinitrogen trioxide • It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C (−6 °F): • NO + NO2    N2O3

  23. NO2 • Nitrogen dioxide • The thermal decomposition of some metal nitrates also affords NO2: • 2 Pb(NO3)2 → 2 PbO + 4 NO2 + O2

  24. N2O4 • Dinitrogen tetroxide N2O4 ⇌ 2 NO2

  25. Q. NO2 dimerises. A. NO2 contains an odd no. of valence electrons. Thus, it behaves as a typical odd molecule. On dimerisation, it is converted into a more stable N2O4 molecule with an even no. of electrons.

  26. N2O5 • Dinitrogen pentoxide P4O10 + 12 HNO3 → 4 H3PO4 + 6 N2O5

  27. Nitric Acid 1. Nitric acid is made by reacting nitrogen dioxide (NO2) with water. 3 NO2 + H2O → 2 HNO3 +NO 2. Almost pure nitric acid can be made by adding sulfuric acid to a nitrate salt, and heating the mixture with an oil bath. A condenser is used to condense the nitric acid fumes that bubble out of the solution. 2NaNO3 + H2SO4 2HNO3+Na2SO4

  28. On a large scale it can be manufactured by Ostwald`s method.By catalytic (Pt/Rh gauge) oxidation of ammonia with atmospheric oxygen. 4NH3+5O2 4NO+6H2O 2NO+O2 2NO2 3NO2+H2O 2HNO3+NO

  29. Properties of HNO3 • Nitric acid

  30. Chemical Properties of HNO3 • Nitric acid is a strong oxidizing agent. When it undergoes thermal decomposition it yields nascent oxygen as follows: 2HNO3 H2O+2NO2+[O] • Remember:- • The nascent oxygen so formed oxidizes non-metals, metals, inorganic as well as organic compounds etc.

  31. a) With Non-Metals • With hot concentrated nitric acid, non-metals are oxidized to their oxide while the acid itself gets reduced to nitrogen dioxide. • In all the reactions described below, the nascent oxygen is released during the thermal decomposition of the acid, which oxidizes the non-metals.  2HNO3 H2O+2NO2+[O] i) With carbon • Nascent oxygen reacts with carbon to form carbon dioxide. C+2[O] CO2 • The overall reaction is 4HNO3+C 2H2O+4NO2+CO2

  32. ii) With sulphur • Nascent oxygen reacts with sulphur to form sulphur trioxide. S+3[O] SO3 • Sulphur trioxide in turn reacts with water to form sulphuric acid H2O+SO3 H2SO4 • The overall reactions is: S+6HNO3 2H2O+H2SO4+6NO2

  33. iii) With phosphorous • Nascent oxygen reacts with phosphorous to form phosphorous (V) oxide. P4+10[O] P4O10 • Phosphorous (V) oxide in turn reacts with water to form phosphoric acid. 6H20+P4O10 4H3PO4 • The overall reaction is: P4+20HNO3 4H2O+4H3PO4+20NO2

  34. b) With Metals • Nitric acid behaves differently with different metals at different concentrations. i) With sodium, potassium and calcium the reaction is highly explosive. ii) With magnesium and manganese With magnesium and manganese, cold and extremely dilute (1%) nitric acid, reacts to yield hydrogen.

  35. iii) With Copper • With cold dilute nitric acid: Copper reacts with cold and dilute nitric acid to yield copper nitrate, water and nitric oxide. 3Cu+8HNO3 3Cu(NO3)2+4H2O+2NO The formed nitric oxide combines with the oxygen of air to give brown fumes of NO2. 2NO+O2 2NO2 • With concentrated nitric acid (cold or hot): Copper reacts with cold or hot concentrated nitric acid to yield copper nitrate, water and nitrogen dioxide. Cu+4HNO3 Cu(NO3)2+2H2O+2NO2

  36. iv) With Zinc • With cold dilute nitric acid: Zinc reacts with cold and dilute nitric acid to yield zinc nitrate, water and nitric oxide.   3Zn+8HNO3 3Zn(NO3)2+4H2O+2N2O • With concentrated nitric acid (cold or hot): Zinc reacts with cold or hot concentrated nitric acid to yield zinc nitrate, water and nitrogen dioxide. Zn+4HNO3 Zn(NO3)2+2H2O+2NO2

  37. Some metals like Cr, Al do not oxidise in conc. Nitric acid because of the formation of a thin film of oxide on its surface. • Conc. Nitric acid also oxidises non-metals. I2+10 HNO3 2HIO3+10NO2+4H2O C+4HNO3 CO2+2H2O+2NO2 S8+48HNO3 8H2SO4+48NO2+16H2O P4+20HNO3 4H3PO4+20NO2+4H2O

  38. Q. Conc. nitric acid is a strong oxidizing agent and oxidises metals like Cu and Zn. However, metals like Cr and Al do not dissolve in conc. HNO3. A. Due to the formation of passive oxide films on the surface of Cr and Al.

  39. Phosphorus-Allotropic FormsWhite Phosphorus • Translucent, white, waxy solid. • Insoluble in water but soluble in CS2. • Dissolves in boiling NaOH solution. P4+3NaOH+3H2O PH3+3NaH2PO2 • It ignites spontaneously in air at about 50C and at much lower temp. if finely divided. This combustion gives phosphorus (V) oxide:P4+5O2 P4O10

  40. Red Phosphorus It is prepared by heating white phosphorus to about 540 K in an inert atmosphere of nitrogen for several hours which on heating and under high pressure gives black phosphorus. (i) It is a hard crystalline solid without any smell and is poisonous in nature. (ii) It is insoluble in water as well as in carbon disulphide. (iii) It is more stable and relatively less reactive. (iv) It consists of tetrahedral units of P4 linked to one another to constitute linear chains.

  41. Black Phosphorus • It is prepared by heating white phosphorus to about 470 K under high pressure of 1200 atmospheres in inert atmosphere.  (i) It has metallic lustre. (ii) It is most inactive form of phosphorus. (iii) It has a layer type structure in which each layer consists of phosphorus atoms.

  42. Phosphine • Preparation- • Reaction of Calcium phosphide with water or dil. acid. Ca3P2+6H2O 3Ca(OH)2+2PH3 Ca3P2+6HCl 3CaCl2+2PH3 2. Lab. Method- Heating white phosphorus with conc. NaOH in inert atmosphere of CO2.

  43. P4+3NaOH+3H2O PH3+3NaH2PO2 3. From impure phosphine- PH3+HI PH4I (+KOH) KI+H2O+PH3 • Properties- • Slightly soluble in water. • Aqueous solution of phosphine decomposes in light and gives red phosphorus and hydrogen.

  44. 3CuSO4+2PH3 Cu3P2+3H2SO4 • 3HgCl2+2PH3 Hg3P2+3HCl • PH3+HBr PH4Br Q. PH3 is a Lewis base. A. Due to the presence of a lone pair of electrons on the P atom. Q. Bond angle in PH4+ is higher than that of PH3. A. In PH4+, there are 4 bond pairs on the central P atom. Thus, it has a tetrahedral shape with a bond angle of 109.5. However, in PH3, there is a lone pair on the central P atom. Due to lp-bp repulsion, bond angle in PH3 is slightly less than 109.5.

  45. Phosphorus Trichloride Preparation- • Lab method-Heat white phosphorus in current of dry chlorine. P4+6Cl2 4PCl3 2. P4+8SOCl2 4PCl3+4SO2+2S2Cl2

  46. Properties- • PCl3+3H2O H3PO3+3HCl • PCl3+3CH3COOH H3PO3+CH3COCl • PCl3+3C2H5OH H3PO3+C2H5Cl Structure- sp3 hybridisation. Pyramidal structure.

  47. Phosphorus Pentachloride Preparation- • Reaction of white phosphorus with excess of dry chlorine. P4+10Cl2 4PCl5 • P4+10SO2Cl2 4PCl5+10SO2 Properties- • PCl5+H2O POCl3+2HCl POCl3+3H2O H3PO4+3HCl

  48. 2. On heating PCl5 PCl3+Cl2 3. C2H5OH+PCl5 C2H5Cl+POCl3+HCl 4. 2Ag+PCl5 2AgCl+PCl3 5. Sn+2PCl5 SnCl4+2PCl3 Structure- In gaseous and liquid phases, it has a trigonal bipyramidal structure. 3 equatorial P-Cl bonds are equivalent while 2 axial bonds are longer than equatorial bonds.

  49. Q. PCl3 fumes in the presence of moisture. A. This is due to the formation of HCl. PCl3 + 3H2O  H3PO4 + 3HCl Q. All the 5 P-Cl bonds in PCl5 are not equivalent. A. PCl5 molecule is trigonal bipyramidal in shape. The 3 equatorial bonds are of the same length but the 2 axial bonds are longer due to repulsion between bond pairs of the axial and equatorial bonds. Q. PCl5 in the gaseous and solid states, respectively, do not have the same geometry. A. PCl5 (g) is trigonal bipyramidal in shape. In the solid state, PCl5 is ionic with tetrahedral [PCl4]+ cation and octahedral [PCl6]- anion.

  50. Oxoacids of Phosphorus Oxidation State/ Formula /Name/ Acidic Protons/Compounds +1/H3PO2 /hypophosphorous acid /1/ acid, salts +3/H3PO3/(ortho)phosphorous acid/ 2/ acid, salts +5/(HPO3)n/metaphosphoric acids/ n /salts (n=3,4) +5/H5P3O10/triphosphoric acid /3/ salts +5/H4P2O7/pyrophosphoric acid /4/ acid, salts +5/H3PO4/(ortho)phosphoric acid/ 3/ acid, salts

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