P block elements

By Mr.Vijaykumar Nazare
email = [email protected]

1. P block elements Mr. Vijaykumar Nazare

2. The p- Block Elements p -Block Elements ( Group 13 to 18 ) s- Block Elements (group 1 and 2 ) s and p- block Representative Elements or Main Group Elements . 27-Oct-19 3 Vijaykumar Nazare The p- Block Elements

3. The p- Block Elements Outermost electronic configuration varies from ns 2 np 1 to ns 2 np 6 Group 13 elements--- ns 2 np 1 Group 14 elements--- ns 2 np 2 27-Oct-19 4 Vijaykumar Nazare The p- Block Elements

4. The p- Block Elements   Most of p-Block elements are non-metals.     They have variable oxidation states.     They form acidic oxides     They impart no characteristic colour to the flame      Generally they form covalent compounds. Halogens form salts with alkali metals      Main points ( properties) 27-Oct-19 5 Vijaykumar Nazare The p- Block Elements

5. The p- Block Elements        They have high ionization potentials.      They have very large electron gain enthalpies.      They are solids/liquids/gases at room temperature (Br is liquid)      The aqueous solutions their oxides are acidic in nature. Main points (properties ) cont…d 27-Oct-19 6 Vijaykumar Nazare The p- Block Elements

6. THE p -BLOCK ELEMENTS why p-block elements consist of only six groups ? The number of p orbitals is three therefore, the maximum number of electrons that can be accommodated in a set of p orbitals is six. Therefore, there are six groups of p–block elements in the periodic table numbering from 13 to 18. 27-Oct-19 7 Vijaykumar Nazare The p- Block Elements

7. Boron, carbon , nitrogen , oxygen , fluorine and helium head the groups. Their valence shell electronic configu ration is ns 2 np 1-6 (except for He). 27-Oct-19 8 Vijaykumar Nazare The p- Block Elements

8. The important oxidation states exhibited by p-block elements are shown in Tab le 27-Oct-19 9 Vijaykumar Nazare

9. Property N P As Sb Bi Atomic number 7 15 33 51 83 Atomic mass/g mol -1 14.01 30.97 74.92 121.75 208.98 Electronic configuration [He]2S 2 2p 3 [Ne]3S 2 2p 3 [Ar]3d 10 4s 2 4p 3 [Kr]4d 10 5s 2 5p 3 [ Xe ]4f 14 5d 10 6s 2 6p 3 Ionisation       I enthalpy      II (Δ i H/(kj      III mol -1 ) 1402 2856 4577 1012 1903 2910 947 1798 2736 834 1595 1610 703 1610 2466 Electronegetivity 3.0 2.1 2.0 1.9 1.9 Covalent radius/pm a 70 110 121 141 148 Ionic radius/pm 171 b 212 b 222 b 76 c 103 c Melting point/K 63* 317 d 1089 e 904 544 Boiling point/K 77.2* 554 d 888 f 1860 1837 Density/[g cm -3 (298 K)] 0.879 g 1.823 5.778 h 6.697 9.808 Table 7.1: Atomic and Physical Properties of Group 15 Elements 27-Oct-19 Vijaykumar Nazare 10

10. Group 15 elements Electronic Configuration The valence shell electronic configuration ns 2 np 3 . The s orbital is completely filled and p orbitals are half-filled , making their electronic configuration extra stable . +3 and +5 oxidation state . 27-Oct-19 Vijaykumar Nazare 11

11. 7.1.3 Atomic and Ionic Radii Covalent and ionic (in a particular state) radii increase in size down the group . There is a considerable increase in covalent radius from N to P . As to Bi only a small increase in covalent radius is observed due to the presence of completely filled d orbitals and/or f orbitals in heavier members. 27-Oct-19 Vijaykumar Nazare 12

12. 7.1.4 Ionisation Enthalpy Ionisation enthalpy : decreases down the group due to gradual increase in atomic size. Ionisation enthalpy of group 15 elements greater than group 14 elements: Because of the extra stable half-filled p orbitals electronic configuration and smaller size of group 15 elements . Increase in magnitude of effective nuclear charge. 27-Oct-19 Vijaykumar Nazare 13

13. 7.1.5 Electronegativity The electronegativity value, in general, decreases down the group with increasing atomic size . However, amongst the heavier elements, the difference is not that much pronounced. 27-Oct-19 Vijaykumar Nazare 14

14. 7.1.6 Physical Properties Polyatomic nature : Dinitrogen diatomic gas while all others are solids (Polyatomic P 4 ). Metallic character : increases down the group. Nitrogen and phosphorus are non-metals, arsenic and antimony metalloids bismuth is a metal. This is due to decrease in ionisation enthalpy and increase in atomic size . The boiling points, increase from top to bottom in the group . The melting point increases upto arsenic and then decreases upto bismuth. 27-Oct-19 Vijaykumar Nazare 15

15. Anomalous properties of nitrogen Anamalous property is due to its small size High electronegativity High ionisation enthalpy Non-availability of d orbitals. 27-Oct-19 Vijaykumar Nazare 16

16. Anomalous property Nitrogen form p π -p π multiple bonds . Bond enthalpy (941.4 kJ mol –1 ) is very high. Heavier elements do not form p π -pπ bonds as their atomic orbitals are so large and diffuse that they cannot have effective overlapping. phosphorus (P–P), arsenic(As–As) and antimony ( Sb – Sb )form single bonds and bismuth forms metallic bonds in elemental state. 27-Oct-19 Vijaykumar Nazare 17

17. Anamalous property N-N single bond is weaker than P-P single bond . Because Bond length is short in N-N . High interelectronic repulsion of the non-bonding electrons. Therefore catenation is weak in nitrogen . 27-Oct-19 Vijaykumar Nazare 18

18. Nitrogen cannot form bond with transition elements : A bsence of d orbitals in its valence shell. Nitrogen cannot form dπ –pπ bond as the heavier elements can e.g., R 3 P = O or R 3 P = CH 2 (R = alkyl group). Phosphorus and arsenic can form dπ –dπ bond with transition metals when their compounds like P(C 2 H 5 ) 3 and As(C 6 H 5 ) 3 act as ligands. 27-Oct-19 Vijaykumar Nazare 19

19. (i) Reactivity towards hydrogen Hydride formation : Group 15 form EH 3 ( E = N, P, As, Sb or Bi ) The hydrides show regular gradation in their properties . Stability : decreases from NH 3 to BiH 3 due to increase in atomic size , decrease in bond dissociation enthalpy . Reducing character :Increases ,due to small bond dissociation enthalpy ,covalent character decreases. Basicity :decreases NH 3 > PH 3 > AsH 3 > SbH 3 > BiH 3 . NH 3 Is strong base :Small size and high electron density, has lone pair . 27-Oct-19 Vijaykumar Nazare 20

20. (ii) Reactivity towards oxygen Form two types of oxides: E 2 O 3 and E 2 O 5 . The oxide in higher oxidation state is more acidic . Their acidic character decreases down the group . Nitrogen atom has small atomic size ,strong pull of electron pair between O-H bond ,releases the H+ ion . Effect decreases as atomic size increases . The oxides of type E 2 O 3 of nitrogen and phosphorus are purely acidic , arsenic and antimony amphoteric , bismuth predominantly basic . 27-Oct-19 Vijaykumar Nazare 21

21. (iii) Reactivity towards halogens Halides formation: M X 3 and MX 5 . Nitrogen does not form pentahalide due to non-availability of the d orbitals in its valence shell , contains only 1 - s and 3- p orbitals . Pentahalides are more covalent than trihalides . All the trihalides (covalent nature) of these elements except those of nitrogen are stable . In case of nitrogen, only NF 3 is known to be stable. Trihalides except BiF 3 are predominantly covalent in nature. 27-Oct-19 Vijaykumar Nazare 22

22. Reactivity towards metals Form binary compounds (having +3 oxidation) Ca 3 N 2 (Calcium Nitride) ,Ca 3 P 2 (Calcium Phosphide) Na 3 As 2 (Sodium Arsenide ), Zn 3 Sb 2 ( ZincAntimonide ) Mg 3 Bi 2 (Magnesium Bismuthide ) 27-Oct-19 Vijaykumar Nazare 23

23. Though nitrogen exhibits +5 oxidation state, it does not form pentahalide . Give reason . Solution Nitrogen with n = 2, has s and p orbitals only. It does not have d orbitals to expand its covalence beyond four. That is why it does not form pentahalide . PH 3 has lower boiling point than NH 3 . Why? Solution Unlike NH 3 , PH 3 molecules are not associated through hydrogen bonding in liquid state. That is why the boiling point of PH 3 is lower than NH 3 . 27-Oct-19 Vijaykumar Nazare 24

24. 7.2 Dinitrogen Preparation :( NH 4 CI, NaNO 2 / (NH 4 ) 2 Cr 2 O 7 / Ba(N 3 ) 2 ) Laboratory : dinitrogen is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite . NH 4 CI( aq ) + NaNO 2 ( aq ) → N 2 (g) + 2H 2 O(l) + NaCl ( aq ) It can also be obtained by the thermal decomposition of ammonium dichromate. Very pure nitrogen : thermal decomposition of sodium or barium azide . Ba (N 3 ) 2 → Ba + 3N 2 27-Oct-19 Vijaykumar Nazare 25

25. Properties Dinitrogen : colourless , odourless , tasteless and non-toxic gas. Two stable isotopes : 14 N and 15 N. Low Solubility in water , low freezing and boiling points Inert at room temperature because of the high bond enthalpy of N ≡N bond. Reactivity increases rapidly with rise in temperature. At higher temperatures, form ionic nitrides and with non-metals, covalent nitrides. Reaction with hydrogen to form ammonia: Reaction with dioxygen (at about 2000 K) form nitric oxide, NO. 27-Oct-19 Vijaykumar Nazare 26

26. Uses: Manufacture of ammonia and industrial chemicals containing nitrogen, (e.g., calcium cyanamide ). Finds use where an inert atmosphere is required (e.g., in iron and steel industry, inert diluent for reactive chemicals). Refrigerant to preserve biological materials, food items and in cryosurgery etc. 27-Oct-19 Vijaykumar Nazare 27

27. Ammonia Preparation Ammonia : present in air and soil formed by decay of nitrogenous organic matter e.g., urea. NH 2 CONH 2 + 2H 2 O → ( NH 4 ) 2 CO 3 → 2NH 3 + H 2 O + CO 2 On a small scale ammonia is obtained from ammonium salts which decompose when treated with caustic soda or lime. 2NH 4 Cl + Ca(OH) 2 → 2NH 3 + 2H 2 O + CaCl 2 (NH 4 ) 2 SO 4 + 2NaOH → 2NH 3 + 2H 2 O + Na 2 SO 4 On a large scale , ammonia is manufactured by Haber’s process. N 2 (g) + 3H 2 (g) → 2NH 3 (g) Δ f H ° = – 46.1 kJ mol −1 27-Oct-19 Vijaykumar Nazare 28

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29. Properties of Ammonia colourless gas with a pungent odour In the solid and liquid states, it is associated through hydrogen bonds , high melting and boiling points . Structure : trigonal pyramidal . It has three bond pairs and one lone pair of electrons . Ammonia gas : highly soluble in water. Its aqueous solution is weakly basic due to the formation of OH − ions. NH 3 (g) + H 2 O(l) → NH 4 + ( aq ) + OH − ( aq ) Lewis base : The presence of lone pair of electrons on nitrogen atom. donates the electron pair and forms complex with metal ions . Applications :detection of metal ions such as Cu 2+ , Ag + 27-Oct-19 Vijaykumar Nazare 30

30. Applications Cu 2+ ( aq ) + 4NH 3 ( aq ) → [Cu(NH 3 ) 4 ] 2+ ( aq ) (blue)                                 (deep blue) Ag + ( aq ) + Cl − ( aq ) → AgCl ( s ) ( colourless )                (white ppt ) AgCl ( s ) + 2NH 3 ( aq ) → Ag ( NH 3 ) 2 Cl ( aq ) (white ppt )                 ( colourless ) 27-Oct-19 Vijaykumar Nazare 31

31. Uses: Produce nitrogenous fertilisers (ammonium nitrate, urea, ammonium phosphate and ammonium sulphate ) Manufacture of some inorganic nitrogen compounds , eg . nitric acid. Liquid ammonia is also used as a refrigerant. 27-Oct-19 Vijaykumar Nazare 32

32. Oxides of Nitrogen 27-Oct-19 Vijaykumar Nazare 33

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34. Nitric Acid Nitrogen forms oxoacids : H 2 N 2 O 2 ( hyponitrous acid) HNO 2 (nitrous acid) and HNO 3 (nitric acid). HNO 3 is the most important. Preparation: Laboratory :heating KNO 3 or NaNO 3 and concentrated H 2 SO 4 in a glass retort. NaNO 3 + H 2 SO 4 → NaHSO 4 + HNO 3 Large scale : Ostwald’s process. catalytic oxidation of NH 3 by atmospheric oxygen. Nitric oxide thus formed combines with oxygen giving NO 2 . 2NO ( g ) + O 2 ( g )→2NO 2 ( g ) Nitrogen dioxide so formed, dissolves in water to give HNO 3 . 3NO 2 ( g ) + H 2 O ( l ) → 2HNO 3 ( aq ) + NO ( g ) 27-Oct-19 Vijaykumar Nazare 35

35. Properties It is a colourless liquid, Structure : planar molecule . Nitric acid behaves as a strong acid giving hydronium and nitrate ions. HNO 3 ( aq ) + H 2 O(l) → H 3 O + ( aq ) + NO 3 - ( aq ) Strong oxidising agent and attacks most metals except noble metals such as gold and platinum. 3Cu + 8 HNO 3 (dilute) → 3Cu(NO 3 ) 2 + 2NO + 4H 2 O Cu + 4HNO 3 ( conc. ) → Cu(NO 3 ) 2 + 2 NO 2 + 2H 2 O Zinc reacts with dilute nitric acid to give N 2 O and with concentrated acid to give NO 2 . 4Zn + 10HNO 3 (dilute) → 4 Zn (NO 3 ) 2 + 5H 2 O + N 2 O Zn + 4HNO 3 ( conc. ) → Zn (NO 3 ) 2 + 2H 2 O + 2 NO 2 Some metals (e.g., Cr, Al) do not dissolve in concentrated nitric acid because of the formation of a passive film of oxide on the surface. 27-Oct-19 Vijaykumar Nazare 36

36. Properties Reaction with Non- metals: Iodine is oxidised to iodic acid, carbon to carbon dioxide, sulphur to H 2 SO 4 , and phosphorus to phosphoric acid. I 2 + 10HNO 3 → 2HIO 3 + 10NO 2 + 4H 2 O C + 4HNO 3 → CO 2 + 2H 2 O + 4NO 2 S 8 + 48HNO 3 → 8H 2 SO 4 + 48NO 2 + 16H 2 O P 4 + 20HNO 3 → 4H 3 PO 4 + 20NO 2 + 4H 2 O 27-Oct-19 Vijaykumar Nazare 37

37. Uses: Manufacture of ammonium nitrate for fertilisers and other nitrates for use in explosives and pyrotechnics. Preparation of organic nitro compounds nitroglycerin, trinitrotoluene and other. Other major uses are in the pickling of stainless steel, etching of metals and an oxidiser in rocket fuels. 27-Oct-19 Vijaykumar Nazare 38

38. 27-Oct-19 Vijaykumar Nazare 39 Sr. no White Phosphorus Red Phosphorus Black phosphorus 1 Transparent , waxy solid ,poisonous . Odourless ,non-poisonous white P 4 + 573 K → Red P 4 iron grey lustre Red P 4 + 803 K → α -black P 4 white P 4 + 4373 K → β -black P 4 Two forms α and β 2 insoluble in water but soluble in CS 2 insoluble in water and CS 2 Sublime,opaque,monoclinic 3 Glows in dark Does not Glow in dark Does not glow in dark 4 Burns in air P 4 + 5O 2 → P 4 O 10 β -black P 4 Does not burn in air 5 Less stable ,reactive due to angular strain Less reactive Less reactive 6 tetrahedral P 4 molecule polymeric, chains of P 4 tetrahedra linked together . Layered structure

39. Phosphine PH 3 Preparation : R eaction of calcium phosphide with water or dilute HCl . Ca 3 P 2 + 6 H 2 O → 3Ca(OH) 2 + 2PH 3 Ca 3 P 2 + 6 HCl → 3CaCl 2 + 2PH 3 Laboratory : H eating white phosphorus with concentrated NaOH solution in an inert atmosphere of CO 2 . P 4 + 3NaOH + 3H 2 O → PH 3 + 3NaH 2 PO 2 (sodium hypophosphite) When pure, it is non inflammable but becomes inflammable owing to the presence of P 2 H 4 or P 4 vapours . To purify PH 4 I + KOH → KI + H 2 O + PH 3 27-Oct-19 Vijaykumar Nazare 40

40. Properties Colourless gas with rotten fish smell and highly poisonous . It explodes in contact with oxidising agents like HNO 3 , Cl 2 and Br 2 vapours . Slightly soluble in water. The solution of PH 3 in water decomposes in presence of light giving red phosphorus and H 2 . When absorbed in copper sulphate or mercuric chloride solution, phosphides are obtained. 3CuSO 4 + 2PH 3 → Cu 3 P 2 + 3H 2 SO 4 3HgCl 2 + 2PH 3 → Hg 3 P 2 + 6HCl Phosphine is weakly basic and like ammonia, gives phosphonium compounds with acids e.g., PH 3 + HBr → PH 4 Br 27-Oct-19 Vijaykumar Nazare 41

41. Uses: The spontaneous combustion of phosphine is technically used in Holme’s signals. Containers containing calcium carbide and calcium phosphide are pierced and thrown in the sea when the gases evolved burn and serve as a signal. It is also used in smoke screens. 27-Oct-19 Vijaykumar Nazare 42

42. Phosphorus Halides T wo types of halides, PX 3 (X = F, Cl , Br, I) and PX 5 (X = F, Cl , Br). Phosphorus Trichloride Preparation : The reaction of white phosphorus with excess of dry chlorine. P 4 + 6Cl 2 → 4PCl 3 Action of thionyl chloride with white phosphorus. P 4 + 8SOCl 2 → 4PCl 3 + 4SO 2 + 2S 2 Cl 2 27-Oct-19 Vijaykumar Nazare 43 Phosphorus Pentachloride Preparation : The reaction of white phosphorus with excess of dry chlorine. P 4 + 10Cl 2 → 4PCl 5 A ction of SO 2 Cl 2 on phosphorus. P 4 + 10SO 2 Cl 2 → 4PCl 5 + 10SO 2

43. Properties Phosphorus Trichloride Colourless oily liquid hydrolysed in presence of moisture. PCl 3 + 3H 2 O →H 3 PO 3 + 3HCl Reacts with organic compounds containing – OH group. 3CH 3 CO OH + P Cl 3 → 3CH 3 COCl +H 3 PO 3 3C 2 H 5 OH + P Cl 3 → 3C 2 H 5 Cl + H 3 PO 3 4. It has a pyramidal shape sp3 . 27-Oct-19 Vijaykumar Nazare 44 Phosphorus Pentachloride Yellowish white powder Hydrolyses in presence of moisture . PCl 5 + H 2 O → POCl 3 + 2HCl POCl 3 + 3H 2 O → H 3 PO 4 + 3HCl Reacts with organic compounds containing –OH group . C 2 H 5 OH + PCl 5 → C 2 H 5 Cl + POCl 3 + HCl CH 3 CO OH + PCl 5 → CH 3 COCl + POCl 3 + HCl 5. Trigonal bipyramidal sp3d

44. Metals on heating with PCl 5 . 2Ag + PCl 5 → 2AgCl + PCl 3 Sn + 2PCl 5 → SnCl 4 + 2PCl 3 Trigonal bipyramidal structure .Two axial bonds are longer than equatorial bonds. This is due to the fact that the axial bond pairs suffer more repulsion as compared to equatorial bond pairs. [PCl 4 ]+ is tetrahedral and the anion, [PCl 6 ]- octahedral 27-Oct-19 Vijaykumar Nazare 45

45. Name Formula Oxidation state of phosphorus Characteristics bonds and their number Preparation Hypophosphorus ( phosphinic ) H 3 PO 2 +1 One P – OH Two P – OH One P = O white P 4 + alkali Orthophosphorous ( phosphonic ) H 3 PO 3 +3 Two P – OH One P – OH One P = O P 2 O 3 Pyrophosphorous H 4 P 2 O 5 +3 Two P – OH two P – OH Two P = O PCl 3 + H 3 PO 3 Hypophosphoric H 4 P 2 O 6 +4 Four P – OH two P – OH One P = O red P 4 + alkali Orthophosphoric H 3 PO 4 +5 Three P – OH One P – OH P 4 O 10 +H 2 O Pyrophosphoric H 4 P 2 O 7 +5 Two P – OH Two P – OH One P-O-P heat phosphoric acid Metaphosphoric (HPO 3 ) n +5 Three P – OH Three P – OH Three P-O-P phosphorus acid + Br 2 , heat in a sealed tube Table 7.5: Oxoacids of Phosphorus 27-Oct-19 Vijaykumar Nazare 46

46. Oxoacids of Phosphorus 27-Oct-19 Vijaykumar Nazare 47

47. Acids having P–H bond have strong reducing properties. Thus, hypophosphorous acid H 3 PO 2 is a good reducing agent as it contains two P–H bonds and reduces. 4 AgNO 3 + 2H 2 O + H 3 PO 2 → 4Ag + 4HNO 3 + H 3 PO 4 These P–H bonds are not ionisable to give H + and do not play any role in basicity. H atoms which attached with oxygen in P–OH form are ionisable and cause the basicity. Thus, H 3 PO 3 and H 3 PO 4 are dibasic and tribasic , respectively as the structure of H 3 PO 3 has two P–OH bonds and H 3 PO 4 three. 27-Oct-19 Vijaykumar Nazare 48

48. Group 16 Elements Oxygen, sulphur , selenium, tellurium and polonium(radioactive) .( chalcogens – ore forming ) Derived from Greek word for brass and points to the association of sulphur and its congeners with copper. C opper minerals contain oxygen or sulphur and other members of the group. Present I earth crust , gypsum,epsum,pyrite,zinc blend ,H2S in volcanoes,protein,garlic,onion,hair . 27-Oct-19 Vijaykumar Nazare 49

49. Electronic Configuration : ns 2 np 4 Atomic and Ionic Radii : Increases Due to increase in the number of shells Ionisation Enthalpy : Decreases due to increase in size . Grop16 has lower I.E than Group15 . due to the fact that Group 15 elements have extra stable half- filled p orbitals electronic configurations. 27-Oct-19 Vijaykumar Nazare 50

50. Electron Gain Enthalpy : Because of the compact nature of oxygen atom (small size) e-e repulsion , it has less negative electron gain enthalpy than sulphur . However, from sulphur onwards the value again becomes less negative upto polonium due to increase in size. Electronegativity : F >O >N electronegativity decreases with an increase in atomic number or size . Metallic character increases from oxygen to polonium. 27-Oct-19 Vijaykumar Nazare 51

51. Peoperty O S Se Te Po Atomic number 8 16 34 52 84 Atomic mass/g mol -1 16.00 32.06 78.96 127.60 210.00 Electronic configuration [He]2s 2 2p 4 [Ne]3s 2 3p 4 [Ar]3d 10 4s 2 4p 4 [Kr]4d 10 5s 2 5p 4 [Ar]4f 14 5d 10 6s 2 6p 4 Covalent radius/(pm) a 66 104 117 137 146 Ionic radius, E 2- /pm 140 184 198 221 230 b Electron gain enthalpy,/ Δ eg H kJ mol -1 -141 -200 -195 -190 -174 Ionisation enthalpy ( Δ i H i )/kJ mol -1 1314 1000 941 869 813 Electronegetivity 3.50 2.44 2.48 2.01 1.76 Density /g cm -3 (298 K) 1.32 c 2.06 d 4.19 e 6.25 - Melting point/K 55 393 f 490 725 520 Boiling point/K 90 718 958 1260 1235 Oxidation states -2,-1,1,2 -2,2,4,6 -2,2,4,6 -2,2,4,6 2,4 Table 7.6: Some Physical Properties of Group 16 Elements 27-Oct-19 Vijaykumar Nazare 52

52. Physical Properties Radioactive Exhibit allotropy Melting and boiling point increases due to increase in atomic mass . 27-Oct-19 Vijaykumar Nazare 53

53. Chemical Properties Oxidation state : -2 ,-1 ,+2 ,+4 ,+6 +2 OF 2 Oxygen does not show +4 and +6 O.S due to lack of d-orbitals . Stability of +6 oxidation state in higher elements due to inner pair effect . 27-Oct-19 Vijaykumar Nazare 54

54. Anomalous behaviour of oxygen Small size ,high I.E. and high electronegativity. The absence of d orbitals in oxygen limits its covalency to four ,rarely exceeds two. On the other hand, in case of other elements of the group, the valence shells can be expanded and covalence exceeds four. 27-Oct-19 Vijaykumar Nazare 55

55. Reactivity with hydrogen Hydrides of the type H 2 E (E = O, S, Se, Te, Po). acidic character: increases from H 2 O to H 2 Te. Due to decrease in bond (H–E) dissociation enthalpy . Thermal stability : decrease bond (H–E) dissociation enthalpy decreases. Reducing property : character increases from H 2 S to H 2 Te. Bond length increases . 27-Oct-19 Vijaykumar Nazare 56

56. Reactivity with oxygen Oxides : EO 2 and EO 3 ( E = S, Se, Te , Po ) Ozone (O 3 ) and sulphur dioxide (SO 2 ) and ( SO 3 ) are gases while selenium dioxide (SeO 2 ) is solid. Reducing property : of dioxide decreases from SO 2 to TeO 2 . Besides EO 2 type, sulphur , selenium and tellurium also form EO 3 type oxides (SO 3 , SeO 3 , TeO 3 ). Both types of oxides are acidic in nature. 27-Oct-19 Vijaykumar Nazare 57

57. Reactivity towards the halogens Type : EX 6 , EX 4 and EX 2 . Stability : decreases in the order F − > Cl − > Br − > I − . Hexahalides : hexafluorides are only stable halides. gaseous in nature, octahedral structure sp 3 d 2 . Eg.SF 6 . Tetrafluorides : SF 4 - gas, SeF 4 -liquid and TeF 4 - solid. Sp 3 d hybridisation ,have trigonal bipyramidal ,having lone pair of electrons at equitorial position. All elements except selenium form dichlorides and dibromides . sp 3 hybridisation , tetrahedral structure. 27-Oct-19 Vijaykumar Nazare 58

58. Acidic nature H 2 S is less acidic than H 2 Te. Why? Solution Due to the decrease in bond (E–H) dissociation enthalpy down the group, acidic character increases. 27-Oct-19 Vijaykumar Nazare 59

59. Dioxygen Preparation : Laboratory: heating oxygen containing salts such as chlorates, nitrates and permanganates. (ii) Thermal decomposition : 2Ag 2 O(s) → 4Ag(s) + O 2 (g)       2Pb 3 O4(s) → 6PbO(s) + O 2 (g) 2HgO(s) → 2Hg(l) + O 2 (g)     2PbO 2 (s) → 2PbO(s) + O 2 (g) (iii) Decomposition of H 2 O 2 using manganese dioxide. 2H 2 O 2 ( aq ) → 2H 2 O(l) + O 2 (g) large scale: Electrolysis of water ,release of hydrogen at the cathode and oxygen at the anode. Industrially : from air by first removing carbon dioxide and water vapour and then, the remaining gases are liquefied and fractionally distilled to give dinitrogen and dioxygen . 27-Oct-19 Vijaykumar Nazare 60

60. Properties Colourless and odourless gas, soluble in water. 3 isotopes: 16 O , 17 O and 18 O. Paramanetic Dioxygen reacts with metals and non-metals except some metals ( e.g., Au, Pt) and some noble gases. Reactions : 2Ca + O 2 → 2CaO C + O 2 → CO 2 4Al + 3O 2 → 2Al 2 O 3 2ZnS + 3O 2 → 2ZnO + 2SO 2 P 4 + 5O 2 → P 4 O 10 CH 4 + 2O 2 → CO 2 + 2H 2 O Exothermic reaction ,to initiate the reaction, some external heating is required as bond dissociation enthalpy of oxgyen -oxygen double bond is high (493.4 kJ mol –1 ). 27-Oct-19 Vijaykumar Nazare 61

61. Uses Respiration and combustion processes, oxy acetylene welding (manufacture of steel) Oxygen cylinders in hospitals, high altitude flying and in mountaineering. The combustion of fuels, e.g., hydrazines in liquid oxygen, provides tremendous thrust in rockets.(L.O as oxidiser in rocket fuel) 27-Oct-19 Vijaykumar Nazare 62

62. Simple Oxides Classification : acidic, basic or amphoteric character. An acidic oxide: oxide combines with water give acid. (e.g., SO 2 , Cl 2 O 7 , CO 2 , N 2 O 5 ). SO 2 + H 2 O → H 2 SO 3 (only non-metal oxides are acidic) M etals in high oxidation state have acidic character (e.g.Mn 2 O 7 , CrO 3 , V 2 O 5 ). basic oxides : The oxides which give base with water (e.g., Na 2 O, CaO , BaO ) CaO + H 2 O → Ca (OH) 2 ( metallic oxides are basic) amphoteric oxides : shows both acidic as well as basic character. Eg . Al 2 O 3 Al 2 O 3 (s)+ 6HCl ( aq ) + 9H 2 O ( l ) → 2[ Al(H 2 O) 6 ] 3+ ( aq )+6Cl − ( aq ) Al 2 O 3 ( s ) + 6NaOH ( aq ) + 3H 2 O ( l ) → 2Na 3 [Al(OH) 6 ]( aq ) neutral oxides : neither acidic nor basic. Eg . CO, NO and N 2 O. 27-Oct-19 Vijaykumar Nazare 63

63. Ozone allotropic form of oxygen. Formation : from atmospheric oxygen in the presence of sunlight . ozone layer protects the earth’s surface from excessive concentration of ultraviolet (UV) radiations. Preparation : Stream of oxygen passed through silent electrical discharge, conversion of oxygen to ozone (10%) occurs. 3O 2 → 2O 3 Ozonised oxygen ΔH V (298 K) = +142 kJ mol −1 Endothermic process . 27-Oct-19 Vijaykumar Nazare 64

64. Properties pale blue gas , dark blue liquid and violet-black solid. characteristic smell small concentrations harmless ,higher concentration headache and nausea. Thermodynamically unstable. Strong oxidising agent . decomposition into oxygen results in liberation of heat (ΔH is negative) and increase in entropy (ΔS is positive). large negative Gibbs energy change (ΔG) for its conversion into oxygen. 27-Oct-19 Vijaykumar Nazare 65

65. Nitrogen oxides emitted from supersonic jet aeroplanes depletes ozone layer . NO ( g ) + O 3 ( g ) → NO 2 ( g ) + O 2 ( g ) Use of freons which are used in aerosol sprays and as refrigerants depletes ozone. high concentrations of ozone is explosive. 27-Oct-19 Vijaykumar Nazare 66

66. Uses germicide , disinfectant and for sterilising water . bleaching oils, ivory, flour, starch, etc. oxidising agent in manufacture of potassium permanganate. 27-Oct-19 Vijaykumar Nazare 67

67. Sulphur – Alltropic Forms Rhombic sulphur (α- sulphur ) yellow in colour , m.p . 385.8 K and specific gravity 2.06. formed on evaporating solution of sulphur in CS 2 . Insoluble in water , soluble in CS 2 . stable below 369 K and transforms into β- sulphur above this temperature . Monoclinic sulphur (β- sulphur ) Its m.p . is 393 K and specific gravity 1.98. formed by melting rhombic sulphur in a dish and cooling. It is soluble in CS 2 . stable above 369 K and transforms into α- sulphur below it. At 369 K both the forms are stable. This temperature is called transition temperature. 27-Oct-19 Vijaykumar Nazare 68

68. Both have S 8 molecule , S 8 ring is puckered and has a crown shape . In cyclo-S 6 , the ring adopts the chair form . 27-Oct-19 Vijaykumar Nazare 69

69. Sulphur Dioxide Preparation : Sulphur is burnt in air or oxygen: S(s) + O 2 (g) → SO 2 (g) Laboratory : treating sulphite with dilute sulphuric acid. SO 3 ( aq ) + 2H ( aq ) → H 2 O(l) + SO 2 (g) Industrially : roasting of sulphide ores. 4FeS 2 (s ) + 11O 2 ( g ) → 2Fe 2 O3 ( s ) + 8SO 2 ( g ) 27-Oct-19 Vijaykumar Nazare 70

70. Properties Colourless gas, pungent smell and highly soluble in water , reducing agent. Sulphur dioxide reacting with water, forms sulphurous acid. SO 2 (g) + H 2 O(l) → H 2 SO 3 ( aq ) Sodium hydroxide solution, forming sodium sulphite ,reacts with more sulphur dioxide to form sodium hydrogen sulphite . 2NaOH + SO 2 → Na 2 SO 3 + H 2 O Na 2 SO 3 + H 2 O + SO 2 → 2NaHSO 3 Sulphur dioxide reacts with chlorine in presence of charcoal (catalyst) gives sulphuryl chloride, SO 2 Cl 2 . It is oxidised to sulphur trioxide by oxygen in the presence of vanadium(V) oxide catalyst. SO 2 (g) + Cl 2 (g) → SO 2 Cl 2 (l) 27-Oct-19 Vijaykumar Nazare 71

71. Uses of SO 2 (i) refining petroleum and sugar (ii) bleaching wool and silk and (iii) as an anti- chlor , disinfectant and preservative. To prepare Sulphuric acid, sodium hydrogen sulphite and calcium hydrogen sulphite (industrial chemicals) Liquid SO 2 used as solvent . 27-Oct-19 Vijaykumar Nazare 72

72. Oxoacid of Sulphur +4 +6 +7 +6 27-Oct-19 Vijaykumar Nazare 73

73. Sulphuric Acid Manufacture : ( Contact Process ) (i) burning of sulphur or sulphide ores in air to generate SO 2 . S → SO 2 (ii) conversion of SO 2 to SO 3 by the reaction with oxygen in the presence of a catalyst (V 2 O 5 ) (iii) absorption of SO 3 in H 2 SO 4 to give Oleum (H 2 S 2 O 7 ). exothermic, reversible and the forward reaction low temperature and high pressure . SO 3 + H 2 SO 4 → H 2 S 2 O 7 ( Oleum ) 27-Oct-19 Vijaykumar Nazare 74

74. Flow diagram for H 2 SO 4 27-Oct-19 Vijaykumar Nazare 75

75. Properties of H 2 SO 4 colourless , dense, oily liquid . The chemical reactions due following characteristics: (a) low volatility (b) strong acidic character (c) strong affinity for water (d) ability to act as an oxidising agent. Ionisation of acid in water. H 2 SO 4 ( aq ) + H 2 O(l) → H 3 O + ( aq ) + HSO 4 − ( aq ); K a1 = very large ( K a1 >10) HSO 4 ( aq ) + H 2 O(l) → H 3 O + ( aq ) + SO 4 2− ( aq ) ; K a2 > = 1.2 × 10 −2 Greater value of( K a ), the stronger is the acid. 27-Oct-19 Vijaykumar Nazare 76

76. Properties of H 2 SO 4 because of low volatility used to manufacture more volatile acids . 2 MX + H 2 SO 4 → 2HX + M 2 SO 4 (X = F, Cl , NO 3 ) ( M = Metal) Strong dehydrating agent. Strong oxidising agent. Cu + 2 H 2 SO 4 (conc.) → CuSO 4 + SO 2 + 2H 2 O 3S + 2H 2 SO 4 (conc.) → 3SO 2 + 2H 2 O C + 2H 2 SO 4 (conc.) → CO 2 + 2 SO 2 + 2 H 2 O 27-Oct-19 Vijaykumar Nazare 77

77. Uses of H 2 SO 4 fertilisers (ammonium sulphate , superphosphate). (a) petroleum refining. (b) pigments, paints and dyestuff intermediates . (c) detergent industry . (d) metallurgical applications (e.g., cleansing metals before enameling, electroplating and galvanising . (e) storage batteries . (f) manufacture of nitrocellulose products . (g) a laboratory reagent. 27-Oct-19 Vijaykumar Nazare 78

78. Group 17 Elements Fluorine, chlorine, bromine, iodine and astatine (radioactive). halogens (salt forming or salt producers ). Highly reactive , non-metallic elements . Occurance : Fluorine :Fluorspar CaF 2 , Cryolite Na 3 AlF 6 Cl ,Br ,I :Sea water as salt of Na , K,Mg , Ca , 27-Oct-19 Vijaykumar Nazare 79

79. Electronic Configuration : (ns 2 np 5 ) Atomic and Ionic Radii : smallest atomic radii due to maximum effective nuclear charge. Atomic and ionic radii increase due to increasing number of quantum shells. Ionisation Enthalpy : L ittle tendency to lose electron due to very high ionisation enthalpy. Due to increase in atomic size, ionisation enthalpy decreases down the group. 27-Oct-19 Vijaykumar Nazare 80

80. Electron Gain Enthalpy : Maximum :only one electron less than stable noble gas configurations. N egative electron gain enthalpy of fluorine is less than that of chlorine due to small size of fluorine atom ,strong interelectronic repulsions in 2p orbitals of fluorine , experience less attraction. Electronegativity : Very high due to increase nuclear charge. Decreases down the group due to increase atomic radia . 27-Oct-19 Vijaykumar Nazare 81

81. Peoperty F Cl Br I At a Atomic number 9 17 35 53 85 Atomic mass/g mol -1 19.00 35.42 79.90 126.90 210 Electronic configuration [He]2s 2 2p 5 [Ne]3s 2 3p 5 [ Ar ]3d 10 4s 2 4p 5 [Kr]4d 10 5s 2 5p 5 [Ar]4f 14 5d 10 6s 2 6p 5 Covalent radius/(pm) a 64 99 114 133 - Ionic radius, X - /pm 133 184 196 220 - Ionisation enthalpy ( Δ i H i )/kJ mol -1 1680 1256 1142 1008 - Electron gain enthalpy/kJ mol -1 -333 -349 -325 -296 - Electronegetivity 4 3.2 3.0 2.7 2.2 Δ Hyd H (X - )/kJ mol -1 515 381 347 305 - F 2 Cl 2 Br 2 I 2 - Melting point/K 54.4 172.0 265.8 386.6 - Boiling point/K 84.9 239.0 332.5 458.2 - Density/g cm -3 1.5 (85) c 1.66(203) c 3.19(273) c 4.49(293)d - Distance X- X/pm -3 143 199 228 266 - Bond dissociation enthalpy/(kJ mol -1 158.8 242.2 192.8 151.1 - E V / V e 2.87 1.36 1.09 0.54 - 27-Oct-19 Vijaykumar Nazare 82

82. Physical Properties F,Cl - gases, Br - liquid ,I - solid. melting and boiling points increase with atomic number. C oloured : Due to absorption of radiations in visible region which results in the excitation of outer electrons to higher energy level. By absorbing different quanta of radiation, they display different colours . Eg . F 2 – yellow, Cl 2 - greenish yellow, Br 2 - red and I 2 -violet colour . Bond dissociation enthalpy : F 2 < Cl 2 >Br 2 > I 2 F2 has smaller bond dissociation enthalpy than Cl 2 Due to large electron-electron repulsion among the lone pairs in F 2 Much closer to each other than Cl 2 . 27-Oct-19 Vijaykumar Nazare 83

83. Chemical Properties Oxidation states ,All the halogens exhibit –1 oxidation state. However, chlorine, bromine and iodine exhibit + 1, + 3, + 5 and + 7 oxidation states 27-Oct-19 Vijaykumar Nazare 84

84. Anomalous behaviour of fluorine Small size ionisation enthalpy, electronegativity, and electrode potentials are higher. Non availability of d orbitals in valence shell. ionic and covalent radii, m.p . and b.p . ,low F-F bond dissociation enthalpy and electron gain enthalpy are quite lower than expected. 27-Oct-19 Vijaykumar Nazare 85

85. Reactivity towards hydrogen Affinity for hydrogen decreases from fluorine to iodine. A cidic strength : HF < HCl < HBr < HI. due to decrease in bond (H–X) dissociation enthalpy Reducing character : HF < HCl < HBr < HI. due to decrease in bond (H–X) dissociation enthalpy Stability :due to decrease in bond (H–X) dissociation enthalpy. H–F > H– Cl > H–Br > H–I. 27-Oct-19 Vijaykumar Nazare 86

86. Reactivity towards oxygen Fluorine : OF 2 and O 2 F 2 . Chlorine, bromine and iodine form oxides in +1 to +7 Chlorine oxides, Cl 2 O, ClO 2 , Cl 2 O 6 and Cl 2 O 7 . ClO 2 used as bleaching agent for paper pulp and textiles and water treatment. B romine oxides , Br 2 O, BrO 2 , BrO 3 . I odine oxides , I 2 O 4 , I 2 O 5 , I 2 O 7 . I 2 O 5 is very good oxidising agent and used in estimation of carbon monoxide. 27-Oct-19 Vijaykumar Nazare 87

87. Reactivity towards metals Metal halides: Mg ( s ) + Br 2 ( l ) → MgBr 2 ( s ) The ionic character decreases: MF > MCl > MBr >MI ( M is a monovalent metal)+1 Halides in higher oxidation state – covalent . Eg . SnCl 4 , PbCl 4 , SbCl 5 and UF 6 are more covalent than SnCl 2 , PbCl 2 , SbCl 3 and UF 4 respt . 27-Oct-19 Vijaykumar Nazare 88

88. Fluorine exhibits only –1 oxidation state whereas other halogens exhibit + 1, + 3, + 5 and + 7 oxidation states also. Explain. Solution Fluorine is the most electronegative element and cannot exhibit any positive oxidation state. Other halogens have d orbitals and therefore, can expand their octets and show + 1, + 3, + 5 and + 7 oxidation states also. 27-Oct-19 Vijaykumar Nazare 89

89. Chlorine Chlorine (Greek, chloros = greenish yellow). Preparation (oxidation by oxidising agent) (i) By heating manganese dioxide with conc. hydrochloric acid. MnO 2 + 4HCl → MnCl 2 + Cl 2 + 2H 2 O mixture of common salt and conc. H 2 SO 4 is used in place of HCl . MnO 2 + 4NaCl + 4H 2 SO 4 → MnCl 2 + 4NaHSO 4 + 2H 2 O + Cl 2 (ii) By the action of HCl on potassium permanganate. 2KMnO 4 + 16HCl → 2KCl + 2MnCl 2 + 8H 2 O + 5Cl 2 Manufacture of chlorine (i) Deacon’s process : oxidation of hydrogen chloride gas by atmospheric oxygen in the presence of CuCl 2 (catalyst) at 723 K. (ii) Electrolytic process: electrolysis of brine (concentrated NaCl solution). Chlorine is liberated at anode. It is also obtained as a by–product in many chemical industries. 27-Oct-19 Vijaykumar Nazare 90

90. Properties greenish yellow gas , pungent and suffocating odour . liquefied into greenish yellow liquid ,soluble in water. Reaction with metals and non-metals form chlorides. 2Al + 3Cl 2 → 2AlCl 3 ;          P 4 + 6Cl 2 → 4PCl 3 2Na + Cl 2 → 2NaCl;         S 8 + 4Cl 2 → 4S 2 Cl 2 2Fe + 3Cl 2 → 2FeCl 3 ; affinity for hydrogen : reacts with compounds containing hydrogen to form HCl . H 2 + Cl 2 → 2HCl H 2 S + Cl 2 → 2HCl + S C 10 H 16 + 8Cl 2 → 16HCl + 10C Excess ammonia , chlorine gives nitrogen and ammonium chloride. 8NH 3 + 3Cl 2 → 6NH 4 Cl + N 2 (excess) Excess chlorine : nitrogen trichloride (explosive) is formed NH 3 + 3Cl 2 → NCl 3 + 3HCl (excess)                   27-Oct-19 Vijaykumar Nazare 91

91. Properties Action on alkalies : With cold and dilute alkalies : chloride and hypochlorite . 2NaOH + Cl 2 → NaCl + NaOCl + H 2 O (cold and dilute) hot and concentrated alkalies : chloride and chlorate 6 NaOH + 3Cl 2 → 5NaCl + NaClO 3 + 3H 2 O (hot and conc.) Dry slaked lime : bleaching powder. 2Ca(OH) 2 + 2Cl 2 → Ca( OCl ) 2 + CaCl 2 + 2H 2 O composition of bleaching powder is Ca( OCl ) 2 .CaCl 2 .Ca(OH) 2 .2H 2 O. 27-Oct-19 Vijaykumar Nazare 92

92. Chlorination Photochemical of hydrocarbon Chlorine reacts with hydrocarbons and gives substitution products with saturated hydrocarbons and addition products with unsaturated hydrocarbons. 27-Oct-19 Vijaykumar Nazare 93

93. Properties of Chlorine Strong oxidising agent : oxidises ferrous to ferric , sulphite to sulphate , sulphur dioxide to sulphuric acid and iodine to iodic acid. 2FeSO 4 + H 2 SO 4 + Cl 2 → Fe 2 (SO 4 ) 3 + 2HCl Na 2 SO 3 + H 2 O + Cl 2 → Na 2 SO 4 + 2HCl SO 2 + 2H 2 O + Cl 2 → H 2 SO 4 + 2HCl I 2 + 6H 2 O + 5Cl 2 → 2HIO 3 + 10HCl powerful bleaching agent :bleaching action is due to oxidation. Cl 2 + H 2 O → 2HCl + O Coloured substance + O → Colourless substance 27-Oct-19 Vijaykumar Nazare 94

94. Uses for bleaching woodpulp (required for the manufacture of paper and rayon), bleaching cotton and textiles . extraction of gold and platinum manufacture of dyes, drugs and organic compounds such as CCl 4 , CHCl 3 , DDT, refrigerants, etc. sterilising drinking water . As disinfectant . preparation of poisonous gases such as phosgene (COCl 2 ), tear gas (CCl 3 NO 2 ), mustard gas (ClCH 2 CH 2 SCH 2 CH 2 Cl). 27-Oct-19 Vijaykumar Nazare 95

95. Hydrogen Chloride Preparation : In laboratory :Heating sodium chloride with concentrated sulphuric acid. HCl gas is dried by passing concentrated sulphuric acid. 27-Oct-19 Vijaykumar Nazare 96

96. Properties Colourless ,pungent smelling gas . Soluble : HCl (g) + H 2 O (l) → H 3 O + ( aq ) + Cl − ( aq )      K a = 10 7 High ( K a ) value - strong acid . Reaction with NH 3 : white fumes of NH 4 Cl. NH 3 + HCl → NH 4 Cl aqua regia : three parts of conc HCl + one part of conc HNO 3 used : dissolving noble metals, e.g., gold, platinum. Au + 4H + + NO 3 − + 4Cl − → AuCl − 4 + NO + 2H 2 O 3Pt + 16H + + 4NO 3 + 18Cl − → 3PtCl 6 − + 4NO + 8H 2 O Hydrochloric acid decomposes : salts of weaker acids, e.g., carbonates, hydrogencarbonates , sulphites , etc. Na 2 CO 3 + 2HCl → 2NaCl + H 2 O + CO 2 NaHCO 3 + HCl → NaCl + H 2 O + CO 2 Na 2 SO 3 + 2HCl → 2NaCl + H 2 O + SO 2 27-Oct-19 Vijaykumar Nazare 97

97. Uses Manufacture of chlorine, NH 4 Cl and glucose (from corn starch ) extracting glue from bones and purifying bone black In medicine as laboratory reagent. 27-Oct-19 Vijaykumar Nazare 98

98. Halic (I) acid ( Hypohalous acid) HOF(Hypofluorous acid) HOCl ( Hypochlorous acid) HOBr(Hypobromous acid) HOI( Hypoiodous acid) Halic (III) acid( Halous acid) – HOCIO( chlorous acid) – – Halic (V) acid( Halic acid) – HOCIO 2 (chloric acid) HOBrO 2 (bromic acid) HOIO 2 (ionic acid) Halic (VII) acid( Perhalic acid) – HOCIO 3 ( perchloric acid) HOBrO 3 ( perbromic acid) HOIO 3 (periodic acid) 27-Oct-19 Vijaykumar Nazare 99 Oxoacids of halogens

99. Interhalogen Compounds Halogens react with each other due to electronegativity difference. More electronegative (smaller halogen)– anion Less electronegative (higher halogen) - cation Types : XX’ , XX’ 3 , XX’ 5 and XX’ 7 where X - halogen of larger size , more electropositive and X’ – halogen of smaller size . Ratio of X and X’ increases ,number of atoms per molecule also increases . eg . IF 7 Preparation : direct combination of halogen on lower interhalogen compounds. 27-Oct-19 Vijaykumar Nazare 100

100. Type Formula Physical state and color Structure XX’ 1 ClF BrF IF a BrCl b ICl IBr colorless gas pale brown gas detected spectroscopically gas ruby red solid(α-form) brown red solid (β – form) Black solid - - - - - - XX’ 3 ClF 3 BrF 3 IF 3 ICl c 3 colorless gasyellow green liquidyellow powder orange solid Bent T-shaped Bent T-shaped Bent T-shaped(?) Bent T-shaped(?) XX’ 5 IF 5 BrF 5 ClF 5 colorless gas but solid below 77 K colorless liquidsquare pyramidal square pyramidal square pyramidal XX’ 7 IF 7 colorless gas pentagonal bipyramidal 27-Oct-19 Vijaykumar Nazare 101

101. Deduce the molecular shape of BrF 3 on the basis of VSEPR theory. Solution The central atom Br has seven electrons in the valence shell. Three of these will form electron- pair bonds with three fluorine atoms leaving behind four electrons. Thus, there are three bond pairs and two lone pairs. According to VSEPR theory, these will occupy the corners of a trigonal bipyramid . The two lone pairs will occupy the equatorial positions to minimise lone pair-lone pair and the bond pair- lone pair repulsions which are greater than the bond pair-bond pair repulsions. In addition, the axial fluorine atoms will be bent towards the equatorial fluorine in order to minimise the lone-pair-lone pair repulsions. The shape would be that of a slightly bent ‘T’. 27-Oct-19 Vijaykumar Nazare 102

102. Properties of interhalogens Covalent and diamagnetic . Volatile solids or liquids except ClF gas . Inter halogen compounds are more reactive due to week X-X’ bond than X-X bond (F-F) Hydrolysis : XX’ + H2O → HX’ + HOX 27-Oct-19 Vijaykumar Nazare 103

103. Uses non aqueous solvents . fluorinating agents. ClF 3 and BrF 3 are used for the production of UF 6 in the enrichment of 235 U. U(s) + 3ClF 3 (l) → UF 6 (g) + 3ClF(g) 27-Oct-19 Vijaykumar Nazare 104

104. Group 18 Elements helium , neon , argon , krypton , xenon and radon . chemically unreactive. They form very few compounds - noble gases. Why are the elements of Group 18 known as noble gases ? Solution valence shell orbitals completely filled . react with a few elements only under certain conditions. Therefore, they are now known as noble gases. 27-Oct-19 Vijaykumar Nazare 105

105. Electronic Configuration : ns 2 np 6 , helium 1s 2 Ionisation Enthalpy : very high Due to stable electronic configuration. decreases down the group with increase in atomic size. Atomic Radii : increase down the group with increase in atomic number. Larger than group 17 due to e-e repulsion . Electron Gain Enthalpy : large positive values . stable electronic configurations, no tendency to accept the electron . 27-Oct-19 Vijaykumar Nazare 106

106. Physical Properties Monoatomic , colourless , odourless and tasteless. sparingly soluble in water . low melting and boiling points : because interatomic interaction in elements is weak dispersion forces. Helium can diffuse through rubber , glass or plastic . 27-Oct-19 Vijaykumar Nazare 107

107. Chemical Properties Least reactive (inertness to chemical reactivity ) Due to (i) The noble gases except helium (1s 2 ) have completely filled ns 2 np 6 electronic configuration in their valence shell. (ii) high ionisation enthalpy and more positive electron gain enthalpy. (a) Xenon-fluorine compounds Xenon forms three binary fluorides, XeF 2 , XeF 4 and XeF 6 XeF 6 can also be prepared by the interaction of XeF 4 and O 2 F 2 at 143K. XeF 4 + O 2 F 2 → XeF 6 + O 2 XeF 2 , XeF 4 and XeF 6 are colourless crystalline solids. powerful fluorinating agents. Hydrolyses: XeF 2 is hydrolysed to give Xe , HF and O 2 . 2XeF 2 (s) + 2H 2 O(l) → 2Xe (g) + 4 HF( aq ) + O 2 (g) 27-Oct-19 Vijaykumar Nazare 108

108. Structures 27-Oct-19 Vijaykumar Nazare 109

109. Uses Helium: non-inflammable and light gas . filling balloons for meteorological observations. used in gas-cooled nuclear reactors . Liquid He : cryogenic agent . produce and sustain powerful superconducting magnets for NMR and MRI . diluent for oxygen in modern diving apparatus because of its very low solubility in blood.(scuba divers) Neon: discharge tubes and fluorescent bulbs for advertisement display purposes. Neon bulbs :botanical gardens and green houses. Argon: inert atmosphere for metallurgical processes (arc welding of metals or alloys) and for filling electric bulbs. laboratory :handling substances that are air-sensitive. Xenon and Krypton : light bulbs designed for special purposes. 27-Oct-19 Vijaykumar Nazare 110