1. CH 124 B ASIC I NORGANIC C HEMISTRY Ms. RIPANDA. A.S asharipanda7@gmail.com 6/29/2020 1

2. C OURSE C ONTENT 10 CREDITS Chemistry of Hydrogen: Properties and uses of Isotopes and isomers of Hydrogen, heavy water and hydrides, hydrogen bonding. For each group of elements (Groups 1, 2, 13, 14, 15, 15, 16, 17, 18): Physical and chemical properties based on electronic configuration, occurrence, extraction and uses. 6/29/2020 2

3. Chemistry of the following in each group of elements: Oxides, hydroxides, halides, salts of oxoacids, hydrides and carbides, solubility and aqueous chemistry, metal-ammonia solutions, chlor - alkali industry (Gps 1,2) Oxides, oxoacids, hydroxides, hydrides, halides, compounds with carbon and nitrogen, electron deficient boranes and carboranes: structure and bonding. 6/29/2020 3

4. C OURSE C ONTENT (Gp 13) Structures of elements and allotropy, oxides, oxoacids, hydroxides, hydride and halides, carbides and silicides, silicones, cyanogin, silicon and tin nitrides, gaseous fuels of carbon, silicate structures and technological applications (Gp 14) Hydrides, halides, oxohalides, nitrides, phosphides, oxides and oxoacids of nitrogen and phosphorous, phosphazenes, urea and phosphate fertilizers (Gp 15) 6/29/2020 4

5. C OURSE C ONTENT Structural aspects of elements and allotropes, Oxides, hydrides, oxoacids, halides, oxohalides, Compounds of sulphur and selenium with Nitrogen (Gp 16) Hydrogen halides, oxides, oxohalides, oxygen fluorides, Inter-halogen compounds(Gp 17) Compounds of Xenon (Gp 18) 6/29/2020 5

6. M ODE OF D ELIVERY AND A SSESSMENT Mode of Delivery: Activity LecturesTutorialsAssignmentsSelf StudyPracticals Hours/week31.50.81.40 Mode of Assessment: 40% Coursework (at least 2 tests); 60% final examination.. Coursework 1.Assignment 10% 2.Test 1 15% 3.Test 2 15% 6/29/2020 6

7. R EFERENCES Housecraft, C.E. and Sharpe, A.G. Inorganic Chemistry, 2 nd Edition, Prentice Hall 2004. Lee, J.D. Concise Inorganic Chemistry, 5 th Edition, Wiley-India, 2010 (Reprint). Greenwood, N.N. and Earnshaw, A. Chemistry of Elements, Elsevier. Cotton, F.A., Wilkinson, G., Murillo, C.A., and Bochmann, M Advanced Inorganic Chemistry, 6 th Edition, Wiley- India, (Second Reprint 2007). 6/29/2020 7

8. H YDROGEN Hydrogen occurs most commonly in the combined state in the form of water, hydrocarbon and carbohydrates. All organic matter contains hydrogen in combination with carbon, nitrogen and oxygen. Position of hydrogen in periodic table It is the first element in periodic table having atomic number 1 and mass number 1.008 amu. The nucleus of hydrogen contain only one proton but no neutron and only one electron present in s orbital of K shell. Hydrogen atom has tendency to lose electron and change into H + ion bear electropositive character like alkali metal and also gain an electron to complete the 1s sub shell, bears electronegative character like halogens. 6/29/2020 8

9. H YDROGEN Resemblance with alkali metals Hydrogen has 1 electron in its outer shell like alkali metals (Group IA). Alkali metals has strong tendency to lose electron from outer shell and change into positive ions (i.e, Li +, Na +, K +, Rb + and Cs + ). Hydrogen also has the same tendency and form H +. Valency of hydrogen and alkali metals are 1. Hydrogen forms stable oxide (H 2 O) and peroxide (H 2 O 2 ) like alkali metals oxide (Na 2 O, K 2 O) and peroxide (Na 2 O 2, K 2 O 2 ) Alkali metals and hydrogen are good reducing agent. Differences Hydrogen has strong ionization energy and very small size as compare to alkali metals. 6/29/2020 9

10. H YDROGEN Resemblance with the halogens Hydrogen can also again one electron to complete 1s sub shell and change into H - like halogens (elements of Group VIIA). The ionization energy of hydrogen is comparable with halogens. Hydrogen molecule is diatomic as like halogens. Hydrogen forms hydrides with carbon (eg, CH 4, C 2 H 6 etc.) whereas halogens form halides with carbon (eg, CCl 4, CHCl 3 etc.). Hydrogen in organic compounds can be substituted by halogens. Hydrogen like halogen forms both ionic and covalent bonds. Differences Electron affinity of halogens is much more than hydrogen. Due to above anomalous behavior of hydrogen with alkali metals and halogens, it placed in periodic table independently. 6/29/2020 10

11. ISOMERS OF HYDROGEN Ortho and Para hydrogen Hydrogen molecule have another different kind of isomer, based on the nuclear spin. As we know, in one hydrogen molecule there are two hydrogen atom and each atom has one proton and one electron. Electron revolves around the positive center, and itself also spin in an axis arising an angular momentum.. 6/29/2020 11

12. I SOMERS OF HYDROGEN ……. As like the spin of electrons, the nuclei of hydrogen molecule also spin in its axis. Such spin can be in two ways, either both nuclei or proton (one from each atom) can spin in same direction, or opposite to each other. If both the nuclei spin in same direction then it is called Ortho Hydrogen and if they spin in opposite direction, it is called Para Hydrogen 6/29/2020 12

13. Isomers of hydrogen 6/29/2020 13

14. Ordinary hydrogen molecule is generally a mixture of Ortho and Para hydrogen in 3:1 ratio in room temperature (75 % Ortho and 25 % Para). As the temperature lowers, Para form increases (ortho form decreases) and as temperature increases, Ortho from increases (para form decreases). 6/29/2020 14

15. O RTHO AND P ARA FORM INTERCONVERTION Based on temperature condition and presence of paramagnetic catalyst Applying catalyst like activated charcoal can help in achieving equilibrium between these two isomeric forms Cooling temperature below 25 k can result in 99% Para form because para form is energetically favored in low temperature. However obtaining pure ortho hydrogen is difficult. 6/29/2020 15

16. Is it possible to separate Ortho and Para forms? Yes, it is possible,Ortho and Para forms slightly differs in their physical properties like melting point, vapour pressure etc. Because they have different vapour pressure, they can be separated by applying Gas chromatography or any such analytical tools. 6/29/2020 16

17. H YDROGEN Preparation of hydrogen Hydrogen gas prepared in industries as follow. 2Na + 2K + 2Ca + 3H 2 O (cold) → Na 2 O + K 2 O + Ca 2 O + 3H 2 ↑ Mg + H 2 O (water gas) → MgO + H 2 ↑ Fe or Zn + superheated steam → H 2 ↑ Al, Sn or Zn + caustic alkalies → H 2 ↑ Fe, Zn or Al + dilute acids → H 2 ↑ On commercial scale, it is prepared by Electrolysis of acidic water. Reduction of steam with carbon or iron. Partial catalytic oxidation of crude naphtha and natural gas. 6/29/2020 17

18. H YDROGEN Properties Hydrogen forms stable hydrides with metals and non metals. It forms covalent hydride with non metals and stability of covalent hydride increases with increasing non metal characteristics of elements. Hydrogen forms electrovalent hydrides with metals and stability of electrovalent hydrides increases with increasing metallic characters of elements. Calcium and Lithium hydride are used in portable hydrogen generator since they evolve large amount of hydrogen when added to water. Isotopes of hydrogen Different atoms with identical atomic number but different atomic mass of the same element are known as isotopes. Hydrogen has three isotopes with mass number 1, 2 and 3 i.e., Protium, Deuterium and Tritium respectively. 6/29/2020 18

19. H YDROGEN Protium or ordinary hydrogen This isotope constitutes 99.984 % of total hydrogen available in nature. Deuterium or heavy hydrogen It constitutes about 0.016 % or 6000 atoms of natural hydrogen contain one atom of deuterium. Molecules are diatomic and its nucleus contains 1 proton and 1 neutron having atomic number 1 and mass number 2. Tritium It is formed in upper atmosphere by certain nuclear reaction. It constitutes only 10-15 % of total natural hydrogen. Molecules are diatomic and its nucleus contains 1 proton and 2 neutrons having atomic number 1 and mass number 3. It is radioactive in character. 6/29/2020 19

20. What is isomerism? Explain existance of isomers of hydrogen /hydrogen molecule giving criteria and pictures to suport your answer where applicable? 6/29/2020 20

21. P REPARATION OF DEUTERIUM By chemical methods: Deuterium is obtained from heavy water by the action of sodium metal. However, In this method a part of heavy water changes into sodium deuteroxide and, therefore, complete recovery is not possible. Deuterium can also be obtained by passing vapour of heavy water over heated metal such as zinc or tungsten. 6/29/2020 21

22. C HEMICAL P ROPERTIES Burning in oxygen Like hydrogen, deuterium is combustible and burns in air or oxygen forming deuterium oxide, D2O, which is commonly known as heavy water. Action with halogens It combines with halogens under suitable conditions forming their deuterides which are analogous to the halogen hydra acids. 6/29/2020 22

23. C HEMICAL P ROPERTIES Combination with nitrogen Deuterium combines with nitrogen in presence of a catalyst and forms nitrogen deuterides (ND3), which is similar to ammonia and known as deuteron ammonia. Combination with metals Deuterium combines with alkali metals at high temperature (3630C) forming deuterides which closely ressemble metallic hydride in their chemical properties as well as crystalline structures. 6/29/2020 23

24. C HEMICAL P ROPERTIES Addition reaction with unsaturated hydrocarbon Deuterium gives addition reaction with unsaturated hydrocarbon, when a mixture of deuterium and ethylene is passed over heated nickel, ethylene deuteride is formed which is saturated hydrocarbon like ethane. Exchange reaction Deuterium reacts with H2, NH3, H2O and CH4, at high temperatures and exchanges its hydrogen partially or completely. These reations are catalysed by finely divided Ni or Cr. 6/29/2020 24

25. H EAVY W ATER (D 2 O) I T WAS DISCOVERED BY U REY (1932). H E SHOWED THAT ORDINARY WATER CONTAINS SMALL PROPORTIONS ( ABOUT 1 PARTS IN 5000) OF THE OXIDE OF HEAVY HYDROGEN, D 2 O. Preparation of heavy water The main source of heavy water is the ordinary water from which it is isolated. Generally it is prepared by prolonged electrolysis or fractional distillation. Prolonged electrolysis of ordinary water This method is involved in multistage electrolysis of ordinary water containing alkali. ( eg. NaOH ). The cylindrical vessels made of steel which act as cathode. The cylindrical sheet of nickel which act as anode with a number of holes punched in it. The electrolysis carried out in different stages. In these stage large number of electrolytic cells are used. 6/29/2020 25

26. E LECTROLYTIC CELL 6/29/2020 26

27. S TAGES IN E LECTROLYSIS OF ORDINARY WATER First Stage Thirty electrolytic cells are used in this stage. Each cell is filled with 3% of NaOH solution. The electrolysis is carried out at 72 hrs, in the presence of current at 110 volts. The volume is reduced to 1/6 th of original volume taken. Some hydrogen and oxygen gases are evolved and discarded. The volume left contains about 2.5 % of heavy water. Second Stage In this stage 6 electrolytic cells are used. This stage involves the residue left from the first stage. The gases evolved are burnt and water formed return to the first stage cell. The residual liquids contain 12% of heavy water. 6/29/2020 27

28. Third Stage This stage involves the residue left from the second stage. The gases are burnt and water formed return to the second stage cell. The content of heavy water is raised to about 60%. Fourth Stage This stage involves the residue left from the third stage. The gases are evolved are burnt as usual and sent to third stage cell. Here nearly 99% of heavy water is obtained. Fifth Stage 99% of heavy water is made free from alkali and other impurities by distillation. Here the gases evolved are D2 and O2 are burnt to get 100% pure heavy water. 6/29/2020 28

29. P ROPERTIES OF H EAVY W ATER Physical properties of water and heavy water at 298 K Heavy water is colourless, tasteless and odourless liquid 6/29/2020 29

30. C HEMICAL P ROPERTIES OF H EAVY W ATER A LTHOUGH HEAVY WATER IS CHEMICALLY SIMILAR TO ORDINARY WATER, CHEMICAL REACTIONS OF HEAVY WATER ARE SLOWER THAN THOSE OF ORDINARY WATER. Reaction with metals Alkali metals and alkaline Earth metals react with heavy water to form heavy hydrogen (D 2 ). 6/29/2020 30

31. C HEMICAL P ROPERTIES OF H EAVY W ATER Reaction with metal oxides D 2 O reacts slowly with metal oxides to form corresponding deuteroxides. Reaction with non-metallic oxides Non-metallic oxides react with D 2 O to form corresponding deutero acid. 6/29/2020 31

32. C HEMICAL P ROPERTIES OF H EAVY W ATER Exchange reactions Compounds having labile hydrogen react with heavy water when hydrogen is exchanged by deuterium partially or completely. Reaction with carbides, nitrides, phosphides, arsenides etc. 6/29/2020 32

33. C HEMICAL P ROPERTIES OF H EAVY W ATER Electrolysis A solution of heavy water containing Na2CO3, when electrolysed evolve heavy hydrogen at cathode. Deutero-hydrates Heavy water like ordinary water may be associated with salts as water of crystallization, giving deutero hydrates, e.g., NaSO4.10D2O, CuSO4.5D2O, MgSO4.D2O, etc. Deuterolysis Water brings hydrolysis of certain inorganic salts. D2O gives similar reactions, which are termed deuterolysis. 6/29/2020 33

34. E FFECT OF H EAVY W ATER Biological and physiological effects Heavy water of high concentration retards the growth of plants and animals. For example, tobacco seeds do not grow in heavy water. Pure heavy water kills small fishes, tadpoles and mice when fed. Heavy water has germicide and bactericide properties too. Water containing small quantity of D 2 O acts as a tonic and stimulates vegetable growth. Certain moulds have been found to develop better in heavy water in comparison to ordinary water. 6/29/2020 34

35. U SES OF H EAVY W ATER ► As a neutron moderator ► Fission in uranium-235 is brought by slow speed neutron. Heavy water is used for this purpose in nuclear reactors as moderators. ► For the preparation of deuterium Heavy water produces deuterium on electrolysis or by its decomposition with metals. ► As a tracer compound Heavy water is used as a tracer compound for studying various reaction mechanisms. It has also been used for studying the structure of some oxyacids of phosphorus such as H 3 PO 2 and H 3 PO 3, to determine the number of ionizable hydrogen atoms. 6/29/2020 35

36. END OF LECTURE ONE 6/29/2020 36

37. H YDRIDES The term hydride is commonly named after binary compounds that hydrogen forms with other elements of the periodic table. Hydride compounds form with almost any element, except a few noble gases. The trends and properties vary according to the type of intermolecular force that bonds the elements together, the temperature, its molecular masses, and other components. 6/29/2020 37

38. Hydrides are classified into three major groups, depending on what elements the hydrogen bonds to. The three major groups are covalent, ionic, and metallic hydrides. Formally, hydride is known as the negative ion of a hydrogen, H-, also called a hydride ion. Because of this negative charge, hydrides have reducing, or basic properties. 6/29/2020 38

39. C OVALENT H YDRIDES Covalent hydrides are formed when a hydrogen atom and one or more non-metals form compounds. This occurs when hydrogen covalently bonds to a more electropositive element by sharing electron pairs. These hydrides can be volatile or non-volatile. (Volatile simply means being readily able to be vaporized at low temperatures) 6/29/2020 39

40. Example of a covalent hydride is when hydrogen bonds with chlorine and forms hydrochloric acid ( HCl ). H2(g)+Cl2(g)→2HCl(g)(1) 3H2(g)+N2(g)→2NH3(g)(2) The hydrides of nonmetals on the periodic table become more electronegative as you move from group 13 to 17. This means that they are less capable of donating an electron, and want to keep them because their electron orbital becomes fuller. Instead of donating a H−, they would instead donate a H+ because they are more acidic. 6/29/2020 40

41. 6/29/2020 41

42. ELECTRON DEFICIENT Gp 13 Boron family Boron in Borane (BH 3 ) is 2e- short to complete octet,unstable and exist as dimer. 6/29/2020 42

43. E LECTRON PRECISE Gp 14 C-family Carbon in Methane No lone pair / complete octet 6/29/2020 43

44. E LECTRON RICH Formed by elements of group 15,16,17 Ammonia – one lone pair Water – two lone pair Hydrogen fluoride -three lone 6/29/2020 44

45. 6/29/2020 45

46. I ONIC H YDRIDES Ionic hydrides (also known as saline hydrides or pseudohalides ). Compounds formed between hydrogen and the most active metals, especially with the alkali and alkaline-earth metals of group IA or IIA elements. In this group, the hydrogen acts as the hydride ion ( H− ). Bond with more electropositive metal atoms. Ionic hydrides are usually binary compounds (i.e., only two elements in the compound) and are also insoluble in solutions. 6/29/2020 46

47. 2A(s)+H2(g)→2AH(s) (3) with A as any group 1 metal. A(s)+H2(g)→AH 2 (s) (4) with A as any group 2 metal. Ionic hydrides combine vigorously with water to produce hydrogen gas. 6/29/2020 47

48. M ETALLIC H YDRIDES Metallic hydrides ( interstitial hydrides ) which are formed when Hydrogen bonds with transition metals. One interesting and unique characteristic of these hydrides are that they can be nonstoichiometric, meaning basically that the fraction of H atoms to the metals are not fixed. Nonstoichiometric compounds have a variable composition. 6/29/2020 48

49. The idea and basis for this is that with metal and hydrogen bonding there is a crystal lattice that H atoms can and may fill in between the lattice while some might, and is not a definite ordered filling. Thus it is not a fixed ratio of H atoms to the metals. Even so, metallic hydrides consist of more basic stoichiometric compounds as well. 6/29/2020 49

50. B RØNSTED C ONCEPT OF A CIDS AND B ASES Brønsted-Lowry theory of acid and bases took the Arrhenius definition one step further, as a substance no longer needed to be composed of hydrogen (H + ) or hydroxide (OH - ) ions in order to be classified as an acid or base. For exmaple, consider the following chemical equation: HCl(aq)+NH3(aq)→NH+4(aq)+Cl−(aq)(1) 6/29/2020 50

51. Therefore, HCl is a Brønsted-Lowry acid (donates a proton) while the ammonia is a Brønsted-Lowry base (accepts a proton). Also, Cl - is called the conjugate base of the acid HCl and NH 4 + is called the conjugate acid of the base NH 3. A Brønsted-Lowry acid is a proton (hydrogen ion) donor. A Brønsted-Lowry base is a proton (hydrogen ion) acceptor. 6/29/2020 51

52. In this theory, an acid is a substance that can release a proton (like in the Arrhenius theory) and a base is a substance that can accept a proton. A basic salt, such as Na + F -, generates OH - ions in water by taking protons from water itself (to make HF): F−(aq)+H2O(l) ⇌ HF(aq)+OH−(2) When a Brønsted acid dissociates, it increases the concentration of hydrogen ions in the solution,[H+]; conversely, Brønsted bases dissociate by taking a proton from the solvent (water) to generate [OH−]. 6/29/2020 52

53. Lewis Concept of Acids and Bases In the Lewis theory of acid-base reactions, bases donate pairs of electrons and acids accept pairs of electrons. A Lewis acid is therefore any substance, such as the H + ion, that can accept a pair of nonbonding electrons. In other words, a Lewis acid is an electron-pair acceptor. A Lewis base is any substance, such as the OH - ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor. 6/29/2020 53

54. One advantage of the Lewis theory is the way it complements the model of oxidation-reduction reactions. Oxidation-reduction reactions involve a transfer of electrons from one atom to another, with a net change in the oxidation number of one or more atoms. The Lewis theory suggests that acids react with bases to share a pair of electrons, with no change in the oxidation numbers of any atoms. In many chemical reactions either electrons are transferred from one atom to another, or the atoms come together to share a pair of electrons. 6/29/2020 54

55. P ROPERTIES OF HYDRIDES Some metal nitrides react with hydrogen to produce the metal hydride. o The most important characteristic of ionic hydrides is that they are strong Bronsted bases. o The hydride ion will react with most molecules that contain a hydrogen atom bound to an atom of high electronegativity. 6/29/2020 55

56. H YDRIDES Such molecules include water, alcohols, and ammonia, as illustrated by the following equations: 6/29/2020 56

57. H YDRIDES Because the hydride is a soft Lewis base, most of the complexes contain metal atoms or ions of low charge, and in many cases they are from the second or third transition series. Other complexes containing hydride ligands are the AlH 4 - and BH 4 - ions that are usually contained in compounds such as LiAlH 4 (lithium aluminum hydride) and NaBH 4 (sodium borohydride), these compounds are versatile reducing agents that are frequently used in synthetic organic chemistry. 6/29/2020 57

58. H YDRIDES Although beryllium and magnesium are found in group IIA of the periodic table, they have higher ionization potentials and higher electronegativities than other elements in this group. Because of this, the hydrides of beryllium and magnesium are polymeric covalent materials that have a chain structure in which there are hydrogen bridges between metal atoms: The bonding arrangement of the four H atoms around each Be is approximately tetrahedral 6/29/2020 58

59. H YDRIDES The reaction of magnesium with boron produces a boride Mg 3 B 2. As we shall see later, borides (as well as oxides, nitrides, carbides, etc.) react with water to produce a hydrogen compound of the nonmetal. Thus, the reaction of magnesium boride with water might be expected to produce BH 3, borane, but instead the product is B 2 H 6, This interesting covalent hydride has the structure Each boron atom is surrounded by four hydrogen atoms in an arrangement that is approximately tetrahedral 6/29/2020 59

60. H YDRIDES Diborane can also be prepared by the reaction of BF 3 with NaBH 4. Boron and hydrogen form many compounds and they exhibit unusual structural forms. Covalent hydrides are generally compounds that have low boiling points. Consequently, they are often referred to as volatile hydrides. 6/29/2020 60

61. In some cases, elements having electronegativities too low to give ionic bonding with hydrogen also tend to be unreactive, so that direct combination of the elements is not feasible. 6/29/2020 61

62. In such cases, the procedure just described can be used to prepare the hydride. For example, silicon hydride, SiH 4 (known as silane), can be produced by the reactions. 6/29/2020 62

63. H YDRIDES Silicon forms numerous hydrides that have counterparts in the hydrocarbon series. However, the silanes are named with respect to the number of silicon atoms present. For example, Si 2 H 6 is known as disilane, Si 3 H 8 is trisilane, and so on. The situation is similar for the germanium hydrides. When a metal phosphide undergoes hydrolysis, the product is PH 3, phosphine. For example, However, PH 3 is not the only hydride of phosphorus, and it is not the only product of this reaction. 6/29/2020 63

64. H YDRIDES The other hydride of phosphorus is diphosphine, P 2 H 4, which is produced in the reaction just shown. This compound is spontaneously flammable in air, and it ignites phosphine, which is also flammable. The boron hydrides, silanes, phosphines, and most other covalent hydrides burn readily, some even being spontaneously flammable. 6/29/2020 64

65. There are numerous similarities between ammonia and phosphine, but the latter is a much weaker base. In fact, phosphonium salts are stabilized by large anions that are also the conjugates of strong acids. Accordingly, the most common phosphonium salts are the iodides, bromides, tetrafluoroborates. Phosphine and substituted phosphines are good Lewis bases toward soft Lewis acids, and many coordination compounds of this type are known. 6/29/2020 65

66. H YDRIDES Although active metals form ionic hydrides, many other metals do not. They react when placed in an atmosphere of hydrogen, but the products contain hydrogen atoms in interstitial positions in the lattice. Hydrides of this type are known as the interstitial hydrides. Because the number of interstitial positions that contain hydrogen atoms is not determined by a definite number of chemical bonds, hydrides of this type may not have simple formulas. Typical compositions are represented as CuH 0.96, LaH 2.78, TiH 1.21, TiH 1.7, or PdH 0.62. Hydrides of this type are often called nonstoichiometric hydrides. 6/29/2020 66

67. Although the formation of ionic hydrides is usually exothermic, the formation of interstitial hydrides may have positive enthalpy values. Physical characteristics of interstitial hydrides are determined by the fact that hydrogen atoms in interstitial positions cause some expansion of the lattice but contribute very little mass. 6/29/2020 67

68. Consequently, the interstitial hydrides always have lower densities than the metal itself, even though the crystal structure is normally the same. When interstitial positions contain hydrogen atoms, the flow of electrons in conduction bands within the metal is impeded, so the conductivity is lower than that of the pure metal. Metals are generally malleable and ductile because of the mobility of atoms within the structure. When the interstitial positions contain hydrogen atoms, the ability of the metals to move in the lattice is constrained so the metal hydride is less malleable and ductile. Typically, the hydrides are harder than the metal alone. 6/29/2020 68

69. H YDRIDES A hydride of a transition metal that has an electronegativity of about 1.4 to 1.7 is not ionic, and bonds between the metal atoms and hydrogen atoms in interstitial positions are not really covalent. Causing the hydrogen to enter the interstitial positions requires the separation of H2 molecules that have a bond energy of 432.6 kJ/mol, and that energy is not compensated by forming either ionic or covalent bonds between the hydrogen and the metal 6/29/2020 69

70. As a result, the heat of formation of interstitial hydrides is often positive. For some purposes, it is appropriate to consider interstitial hydrides as being solutions of atomic hydrogen in the metal. Dissolving the hydrogen usually involves separating H 2 molecules, so the metals often function as effective catalysts for hydrogenation reactions. 6/29/2020 70

71. Because hydrogen molecules must become attached to the surface of the metal, the prior treatment of the metal has a great influence on the formation of a hydride. Cracks, pores, and other defects that aid in the adsorption of hydrogen may have been removed by heating and cooling or by the influence of radiation. 6/29/2020 71

72. Active sites may have been generated by mechanical changes in the surface. All of these factors affect the ease with which the formation of the hydride is accomplished. Because the adsorption of a gas on a solid is related to the partial pressure of the gas and the temperature, these factors influence the fraction of the available sites that are occupied by hydrogen. In other words, the stoichiometry of the hydride may depend on the conditions under which it is formed. 6/29/2020 72

73. H YDRIDES The bond angles in NH 3 are approximately 107°, which indicates sp3 hybridization with a small reduction in bond angle arising from the effect of the unshared pair of electrons on the nitrogen atom. In PH3, the bond angle is only about 93°, so the indication is that the phosphorus orbitals are not sp3 hybrids. 6/29/2020 73

74. Although sp3 hybridization should reduce repulsion between electron pairs, the p orbitals on phosphorus are large enough that increasing their size by hybridization reduces the effectiveness of the overlap with hydrogen 1s orbitals. 6/29/2020 74

75. Bond angles in AsH 3 and SbH 3 are slightly smaller than those in PH 3, which would be expected if p orbitals on the central atoms are used in bonding. Thus, the bond angles indicate that although it is appropriate to assume sp3 hybridization in NH 3, it is not the case for the hydrides of the heavier members of group VA. The hydrogen compounds of group VIA follow this trend in bond angles. 6/29/2020 75

76. H YDRIDES 6/29/2020 76

77. Generally heat of formation of hydride decreases down the group, from Li to Cs, but there is slight increase from Na to K why? 6/29/2020 77

78. H YDRIDES 6/29/2020 78

79. H YDROGEN BOND is the electromagnetic attractive interaction between polar molecules, in which hydrogen is bound to a highly electronegative atom, such as nitrogen, oxygen or fluorine. It is not a true bond but a particularly strong dipole-dipole attraction. 6/29/2020 79

80. D ONORS AND A CCEPTORS In order for a hydrogen bond to occur there must be both a hydrogen donor and an acceptor present. The donor in a hydrogen bond is the atom to which the hydrogen atom participating in the hydrogen bond is covalently bonded, and is usually a strongly electronegative atom such as N,O, or F. The hydrogen acceptor is the neighboring electronegative ion or molecule, and must posses a lone electron pair in order to form a hydrogen bond. 6/29/2020 80

81. H YDROGEN BOND 6/29/2020 81

82. W HY DOES A HYDROGEN BOND OCCUR ? Since the hydrogen donor is strongly electronegative, it pulls the covalently bonded electron pair closer to its nucleus, and away from the hydrogen atom. The hydrogen atom is then left with a partial positive charge, creating a dipole-dipole attraction between the hydrogen atom bonded to the donor, and the lone electron pair on the accepton. This results in a hydrogen bond. 6/29/2020 82

83. 6/29/2020 83

84. H YDROGEN BOND It is off two types: Intermolecular hydrogen bonding: Hydrogen-bond attractions occur between two molecules. Intermolecular hydrogen bonding is responsible for the high boiling point of water (100°C) compared to the other group 16 hydrides that have no hydrogen bonds. 6/29/2020 84

85. Intramolecular hydrogen bonding: Hydrogen bond attractions occur in different parts of a single molecule. Intramolecular hydrogen bonding is partly responsible for the secondary and tertiary structure of proteins and nucleic acids. It also plays an important role in the structure of polymers, both synthetic and natural. 6/29/2020 85

86. H YDROGEN B ONDING S TRUCTURE The hydrogen bond (5 to 30 kJ/mole) is stronger than a van der waals interaction, but weaker than covalent or ionic bonds. This type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins. 6/29/2020 86

87. H YDROGEN BOND DONORS AND ACCEPTORS In an intramolecular hydrogen bonding, hydrogen atom acts as hydrogen bond donor whereas other electronegative atom acts as hydrogen bond acceptor. In an intermolecular hydrogen bonding, the molecule contributes hydrogen acts as hydrogen bond donor and those contributes electronegative atom acts as hydrogen bond acceptor. 6/29/2020 87

88. END OF LECTURE TWO 6/29/2020 88

89. B OND STRENGTH Hydrogen bonds can vary in strength from weak (1–2 kJ mol−1) to strong (161.5 kJ mol−1). The strength of intermolecular hydrogen bonds is most often evaluated by measurements of equilibria between molecules containing donor and/or acceptor units, most often in solution The strength of intramolecular hydrogen bonds can be studied with equilibria between conformers with and without hydrogen bonds. 6/29/2020 89

90. T YPICAL ENTHALPIES OF HYDROGEN BONDING IN VAPOR STAGE. F−H…:F (161.5 kJ/mol or 38.6 kcal/mol) O−H…:N (29 kJ/mol or 6.9 kcal/mol) O−H…:O (21 kJ/mol or 5.0 kcal/mol) N−H…:N (13 kJ/mol or 3.1 kcal/mol) N−H…:O (8 kJ/mol or 1.9 kcal/mol) HO−H…:OH (18 kJ/mol or 4.3 kcal/mol) 6/29/2020 90

91. S TRUCTURAL DETAILS The X−H distance is typically ≈110 pm, whereas the H···Y distance is ≈160 to 200 pm. The typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor. 6/29/2020 91

92. S PECTROSCOPY Strong hydrogen bonds are revealed by downfield shifts in the 1 H NMR spectrum. For example, the acidic proton in the enol tautomer of acetylacetone appears at δ H 15.5, which is about 10 ppm downfield of a conventional alcohol. In the IR spectrum, hydrogen bonding shifts the X-H stretching frequency to lower energy (i.e. the vibration frequency decreases). This shift reflects a weakening of the X-H bond. Certain hydrogen bonds - improper hydrogen bonds - show a blue shift of the X-H stretching frequency and a decrease in the bond length. 6/29/2020 92

93. MANIFESTATIONS OF SOLVENT HYDROGEN BONDING Increase in the melting point, boiling point, solubility, and viscosity of many compounds can be explained by the concept of hydrogen bonding. Negative azeotropy of mixtures of HF and water The fact that ice is less dense than liquid water is due to a crystal structure stabilized by hydrogen bonds. 6/29/2020 93

94. Dramatically higher boiling points of NH 3, H 2 O, and HF compared to the heavier analogues PH 3, H 2 S, and HCl, where hydrogen-bonding is absent. Viscosity of anhydrous phosphoric acid and of glycerol Dimer formation in carboxylic acids and hexamer formation in hydrogen fluoride, which occur even in the gas phase, resulting in gross deviations from the ideal gas law. Pentamer formation of water and alcohols in apolar solvents. 6/29/2020 94

95. S PECIAL CASE OF HYDROGEN BONDING Hydrogen attached to carbon can also participate in hydrogen bonding when the carbon atom is bound to electronegative atoms, as is the case in chloroform, CHCl 3. The electronegative atom attracts the electron cloud from around the hydrogen nucleus causes high partial positive charge density on hydrogen which attracts lone pair electrons from other electronegative atom results hydrogen bonding. 6/29/2020 95

96. The hydrogen bond also has some features of covalent bonding, it is strong, directional and produces inter atomic distances shorter than sum of van der Waals radii. These covalent features are more substantial when acceptors bind hydrogen from more electronegative donors. The length of hydrogen bonds depends on bond strength, temperature, and pressure. The bond strength itself is dependent on temperature, pressure, bond angle, and environment 6/29/2020 96

97. Liquid water's high boiling point is due to the high number of hydrogen bonds each molecule can form, relative to its low molecular mass. Owing to the difficulty of breaking these bonds, water has a very high boiling point, melting point, and viscosity compared to otherwise similar liquids not conjoined by hydrogen bonds. Water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of bonds of a water molecule is up to four. 6/29/2020 97

98. H YDROGEN BONDS IN WATER Due to high number of hydrogen bonds in liquid water causes difficulty of breaking these bonds and very high boiling point, melting point, and viscosity compared to similar liquids without hydrogen bonds. Hydrogen fluoride has three lone pairs on the F atom but only one H atom can form only two hydrogen bonds. H−F…H−F…H−F 6/29/2020 98

99. An example of a hydrogen bond is found between water molecules. In a discrete water molecule, there are two hydrogen atoms and one oxygen atom. Two molecules of water can form a hydrogen bond between them that is to say oxygen- hydrogen bonding; the simplest case, when only two molecules are present, is called the water dimer and is often used as a model system. 6/29/2020 99

100. When more molecules are present, as is the case with liquid water, more bonds are possible because the oxygen of one water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with a hydrogen on another water molecule. This can repeat such that every water molecule is H-bonded with up to four other molecules two through its two lone pairs, and two through its two hydrogen atoms 6/29/2020 100

101. Hydrogen bonding strongly affects the crystal structure of ice, helping to create an open hexagonal lattice. The density of ice is less than the density of water at the same temperature ; thus, the solid phase of water floats on the liquid, unlike most other substances. 6/29/2020 101

102. W HY ICE IS LESS DENSER THAN LIQUID WATER AT SAME TEMPERATURE ? Ice floats on water The most energetically favorable configuration of H2O molecules is one in which each molecule is hydrogen-bonded to four neighboring molecules. Owing to the thermal motions, this ideal is never achieved in the liquid, but when water freezes to ice, the molecules settle into exactly this kind of an arrangement in the ice crystal. 6/29/2020 102

103. This arrangement requires that the molecules be somewhat farther apart than would otherwise be the case; as a consequence, ice, in which hydrogen bonding is at its maximum, has a more open structure, and thus a lower density than water. 6/29/2020 103

104. QNS Why water is in liquid form while hydrogen sulphide in gaseous form? Why water is more viscous than hydrogen sulphide? With aid of example differentiate with example intermolecular from Intramolecular hydrogen bond donation. 6/29/2020 104

105. QNS Why Ortho nitro phenol is more volatile than para-nitro phenol? Why ammonia is soluble in water whereas phosphine is less soluble in water? Why ammonia have lower BP than phosphine? Explain the following terms: Hydrogen bond donor Hydrogen bond acceptor 6/29/2020 105

106. C HEMISTRY OF G ROUP IA ( ALKALI METALS ) AND IIA ( ALKALINE EARTH METALS ) General Characteristics  The metals in the first two groups of the periodic table are characterized as “s block” elements because of their outer shells having one and two electrons in an s orbital.  It has valence shell configurations of ns1 and ns 2, respectively. Consequently, the expected pattern for the group IA and IIA elements is the formation of +1 and +2 ions, respectively. 6/29/2020 106

107.  All naturally occurring compounds of these elements contain the atoms are in positive ionic forms.  Charge on the ion divided by its radius, and it gives the so-called charge density of the ion, gives an idea about the salvation of ion and measures of the hardness of ion. 6/29/2020 107

108. General Characteristics A large number of compounds of the group IA and IIA metals occur naturally (NaCl, Na 2 CO 3, CaCO 3, etc.). Lime is produced by heating limestone in enormous quantity. As a result of the decrease in ionization potential, the reactivity of the metals in groups IA and IIA increase in progressing down in the group. 6/29/2020 108

109. The electro negativities of these metals range from about 0.8 to slightly over 1.0 (except for beryllium, which has an electro negativity of 1.6). All are very strong reducing agents that form binary compounds with most nonmetallic elements and even some other metals that have higher electro negativity. These are soluble in liquid ammonia and amines, and the solutions have many interesting characteristics. 6/29/2020 109

110. QNSQNS Explain characteristics of IA and IIA elements in ammonia solution with aid of reactions. By use of charge density of the ion, discuss salvation and hardness of ions of IA and IIA elements. 6/29/2020 110

111. General Characteristics Because the group IA metals are such strong reducing agents and so reactive, they are generally prepared by electrolysis reactions. For example, sodium is produced by the electrolysis of a molten mixture that contains NaCl and CaCl 2. Lithium is produced by the electrolysis of a mixture of LiCl and KCl. The production of potassium is carried out by using sodium as a reducing agent at 850°C. Under these conditions, potassium is more volatile, so the equilibrium is drawn to the right as potassium is removed. Therefore, even though potassium is normally a stronger reducing agent than sodium, removal of the potassium allows the reaction to be carried out efficiently. 6/29/2020 111

112. E LECTRONIC CONFIGURATION Group IA (Alkali metals)Group IIA (Alkaline earth metals) ElementAtomic No.Electronic Configuration ElementAtomic No.Electronic Configuration Li Na K Rb Cs 3 11 19 37 55 [He] 2S 1 [Ne] 3S 1 [Ar] 4S 1 [Kr] 5S 1 [Xe] 6S 1 Be Mg Ca Sr Ba 4 12 20 38 56 [He] 2S 2 [Ne] 3S 2 [Ar] 4S 2 [Kr] 5S 2 [Xe] 6S 2 6/29/2020 112

113. R ELEVANT DATA FOR G ROUP IA AND G ROUP IIA ELEMENTS 6/29/2020 113

114. P HYSICAL P ROPERTIES OF IA GROUP ELEMENTS Physical appearance All the alkali metals are silvery-white, soft and light metals. Density All the elements have close packing of metal atoms in their lattices and because of the comparatively large size of these atoms, they have low densities and gradually increases in moving down the group from Li to Cs. Molar Volumes The ratio of molar mass (g/mol) and densities (g/cm 3 ) is known as molar volume (cm 3 /mol) of the elements. It increases as we move down the group from Li to Cs. 6/29/2020 114

115. P HYSICAL P ROPERTIES OF IA GROUP ELEMENTS Melting points and Boiling points All the alkali metals are soft and having low melting point due to only one valance electron per metal atom. Melting point decreases down the group as volume and size increases. The boiling point also decreases in same order. Atomic and Ionic Radii Both increases progressively down the group and atomic size always greater than the ionic size of same metal atom. Ions of alkali metals are diamagnetic and colorless in nature. Heat of atomization It measures the strength of metal-metal bond in the lattice of an element. It is maximum in the case of Li where as minimum in case of Cs. 6/29/2020 115

116. P HYSICAL P ROPERTIES OF IA GROUP ELEMENTS Ionization energies Amount of energy required to remove an electron from an isolated gaseous atom in its ground state is called ionization energy. As the atomic radius increases on moving down the group from Li to Cs, the outer electron get farther and farther away from the nucleus and therefore ionization energy decreases. Electropositive character The ease of lose valence electron and change in to positive ion is known as electropositive character of metal. As we move down the group, electropositive character increases because of decrease in ionization energy. K and Cs are very highly electropositive elements, they emit electrons even when exposed to light (Photoelectric effect), therefore these elements used in photoelectric cells. 6/29/2020 116

117. P HYSICAL P ROPERTIES OF IA GROUP ELEMENTS Hydration of ions The alkali metals are univalent and forms ionic compounds, ions are extensively hydrated. The smaller the size of the ion, the greater is the degree of hydration. Li ion which is smallest in size and has the highest charge/size ratio among the alkali metal ions, get much more hydrated (holds more water molecule in its hydration sphere). The degree of hydration decreases down the group. The ion having smallest size becomes largest in aqueous medium, therefore the order of ionic size of alkali metal ions in aqueous medium are as under. Li + > Na + > K + > Rb + > Cs + 6/29/2020 117

118. P HYSICAL P ROPERTIES OF IA GROUP ELEMENTS Oxidation states All the alkali metals exhibit an oxidation state of +1 because these metals can loose their outermost electron easily. The second ionization energy is so high that the second electron is very rarely lost. Electronegativities Electropositive character increases down the group therefore electronegativity decreases in the same order. Lattice energy Salts of alkali metals consists of cations and anions only, therefore called ionic solids. The lattice energy of an ionic solid is defined as the energy released when cations and anions in gaseous state brought from infinity to their respective crystal sites to form one mole of ionic crystal. Lattice energies of salt of alkali metals having a given anion decreases with increase in size. 6/29/2020 118

119. P HYSICAL P ROPERTIES OF IA GROUP ELEMENTS Flame colouration On heating an alkali metal or its salt (especially chlorides due to its more volatile nature in a flame), the electrons are excited easily to higher energy levels because of absorption of energy. When these electrons return to their ground states, they emit extra energy in form of radiations which fall in the visible region thereby imparting a characteristic colour to the flame as illustrated below. 6/29/2020 119

120. P HYSICAL P ROPERTIES OF IA GROUP ELEMENTS Flame colouration Alkali metalsFlame colour LiCrimson red NaGolden yellow KPale violet RbViolet CsSky blue 6/29/2020 120

121. P HYSICAL PROPERTIES OF G ROUP IIA ELEMENTS Lattice energies It decreases as atomic number of elements increases MOMCO 3 MF 2 Mg-3923-3178-2906 Ca-3517-2986-2610 Sr-3312-2718-2459 Ba-3120-2614-2367 6/29/2020 121

122. P HYSICAL P ROPERTIES OF IIA GROUP ELEMENTS Nature of metallic bonding: The alkaline earth metal two electrons are involved in the metallic bonding. Moreover, sizes of alkaline earth metal ions are smaller than those of alkali metal ions. Consequently, stronger metallic bonds are formed which result in the close packing of the atoms. Due to the presence of stronger metallic bonds, alkaline earth metals have (a) Higher melting points (b) Higher boiling points (c) Higher densities (d) Harder than the corresponding alkali metals. Molar Volumes: The ratio of molar mass (g/mol) and densities (g/cm3) is known as molar volume (cm3/mol) of the elements. It increases as we move down the group from Be to Ba. 6/29/2020 122

123. P HYSICAL P ROPERTIES OF IIA GROUP ELEMENTS Melting points and Boiling points: All the alkaline earth metals are more harder than alkali metals due to presence of two valance electrons per metal atom. Melting point decreases down the group as volume and size increases. The boiling point also decreases in same order. Atomic and Ionic Radii: Both increases progressively down the group and atomic size always greater than the ionic size of same metal atom. Ions of alkaline earth metals are diamagnetic and colorless in nature. Heat of atomization: It measures the strength of metal- metal bond in the lattice of an element. It is maximum in the case of Be where as minimum in case of Ba. Density: The alkaline earth metals are denser and harder than the corresponding alkali metals. The atoms of alkaline earth metals have smaller size and are hence held by stronger metallic bonds, as compared to alkali metals. Therefore, they are more closely packed in their crystal lattice which accounts for high density and increased hardness of these elements. 6/29/2020 123

124. P HYSICAL P ROPERTIES OF IIA GROUP ELEMENTS Ionization energies: Amount of energy required to remove an electron from an isolated gaseous atom in its ground state is called ionization energy. As the atomic radius increases on moving down the group from Be to Ba, the outer electron get farther and farther away from the nucleus and therefore ionization energy decreases. All the alkaline earth metals has two successive ionization energies i.e, First inonization energy (IE I) and second ionization energy (IE II) upon removal of one and two electrons respectively. IE I are always less than IE II. Oxidation states: All the alkaline earth metals exhibit an oxidation state of +2 because these metals can loose their outermost electrons easily. Electronegativities: Electropositive character increases down the group therefore electronegativity decreases in the same order. 6/29/2020 124

125. P HYSICAL P ROPERTIES OF IIA GROUP ELEMENTS Characteristic flame colouration: Except Be & Mg (due to high ionization energy), the alkaline earth metals impart characteristic colour when introduced into flame of a burner. This property is due to the ease of excitation of their valence electrons. When elements or their compounds are introduced to flame, the electron absorbs energy from the flame and gets excited to higher energy levels. When these electrons return to their ground state, they emit absorbed energy in form of visible light having characteristic wavelengths. Depending upon the wavelength of light emitted, different colours are impart to the flame. Salts (generally chlorides) impart characteristic colours to the Bunsen flame.. IonColour Ca 2+ Brick-red Sr 2+ Crimson Ba 2+ Apple green Ra 2+ Carmine-red 6/29/2020 125

126. P HYSICAL P ROPERTIES OF IIA GROUP ELEMENTS Electropositive or Metallic Character: The alkaline earth metals are highly electropositive and hence metallic and their electropositive or metallic character increases down the group. However they are less electropositive or metallic than the alkali metals. It is due to smaller size and higher ionization energies as compared to alkali metals hence have fewer tendencies to lose electron than those of alkali metals (group I). Like the alkali metals they also form predominantly ionic compounds but tendency of covalency is greater, particularly with Be and Mg because of their smaller atomic and ionic radii. Be forms compounds which are essentially covalent. All the elements show good metallic lusture and high electrical and thermal conductivity. Question: Mg forms Mg 2+, but Na 2+ does not exist. Explain. Solution: Na metal after the loss of one electron attains a noble gas configuration of neon. Therefore, the removal of second electron is energetically unfavourable. Hence, Na 2+ does not exist. 6/29/2020 126

127. E ND OF LECTERE THREE O8.06.2020 6/29/2020 127

128. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Hydrides Most of the group IA and IIA metals form compounds with hydrogen that contain H -, Because they have the characteristics of ionic compounds, known as the saltlike hydrides. However, the hydrides of beryllium and magnesium are quite different because of their being much more covalent. The most important characteristic of the ionic hydrides is the very strong basicity of the hydride ion. Ionic hydrides will remove protons from almost any molecule that contains an OH bond including water, alcohols, and so on, as illustrated by the following equations: 6/29/2020 128

129. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS The H - ion is such a strong base that it will deprotonate NH 3 to generate the amide ion. Ionic hydrides such as NaH and CaH 2 can be used as drying agents because they will remove hydrogen from the traces of water present in many solvents. Lithium aluminum hydride, LiAlH 4, is a versatile reducing agent that is used to carry out many types of reactions in organic chemistry. 6/29/2020 129

130. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Oxides and Hydroxides The group IA metals react with oxygen, but the products are not always the “normal” oxides. Lithium reacts with oxygen in the expected way, However, sodium reacts with oxygen with the product being predominantly the peroxide. The O 2 -- ion is known as the superoxide ion, and it is produced when oxygen reacts with potassium, rubidium, and cesium. 6/29/2020 130

131. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Presumably, the formation of oxides of the larger atoms in group IA is favored when they contain larger anions. It is generally more favorable when crystal lattices are formed from cations and anions of similar size and magnitude of charge. In reactions with oxygen, the lighter members of the group IIA metals give normal oxides, but barium and radium give peroxides. When the oxygen compounds of group IA and IIA metals react with water, strongly basic solutions are produced regardless of whether an oxide, peroxide, or superoxide is involved. 6/29/2020 131

132. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Sodium hydroxide, sometimes referred to as caustic soda or simply caustic, is produced in enormous quantities by the electrolysis of an aqueous solution of sodium chloride. The fact that this is also the reaction used to prepare chlorine makes it especially important. However, sodium hydroxide will react with chlorine as shown in the equation 6/29/2020 132

133. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS In order to prevent this reaction, the products must be kept separated during the electrolysis. Billions of pounds of NaOH are produced annually, and it is used in many processes that require a strong base. Potassium hydroxide is produced by electrolysis of aqueous KCl. Because it is more soluble than NaOH in organic solvents, KOH is widely used in certain types of processes. For example, KOH is used in the production of many types of soaps and detergents. The hydroxides of rubidium and cesium are of little importance compared to those of sodium and potassium, but they are even stronger bases. 6/29/2020 133

134. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS The oxides of the group IIA metals are ionic, so they react with water to produce the hydroxides. However, beryllium oxide is quite different, and it exhibits amphoteric behavior. Magnesium hydroxide is a weak, almost insoluble base that is used as a suspension known as “milk of magnesia” that is a common antacid. 6/29/2020 134

135. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS The utility of the hydroxides of the group IIA metals is limited somewhat because they are only slightly soluble (only about 0.12 grams of Ca(OH) 2 dissolves in 100 grams of water, although it is a strong base). Calcium hydroxide is produced in enormous quantities by the decomposition of limestone, which is followed by the reaction of CaO (lime) with water. Calcium hydroxide is known as hydrated lime or slaked lime, and it is used extensively in some applications because it is less expensive than NaOH or KOH. It reacts with CO 2 to form CaCO 3, which binds particles of sand and gravel together in mortar and cement. 6/29/2020 135

136. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Halides ► Sodium chloride is found in salt beds, salt brines, and sea water throughout the world which is the source of other sodium compounds. A large portion of the sodium chloride consumed in the production of sodium hydroxide. The production of sodium metal involves the electrolysis of the molten chloride, usually in the form of a eutectic mixture with calcium chloride. ► Sodium carbonate is an important material that is used in many ways such as making glass. It was formerly produced from NaCl by means of the Solvay process, in which the overall reaction is ► Solid product (NaHCO 3 ) decomposes when heated to give sodium carbonate. ► Although the Solvay process is still in use in some parts of the world, the chief source of sodium carbonate is the mineral trona, Na 2 CO 3 NaHCO 3 2H 2 O. 6/29/2020 136

137. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Sulfides, Nitrides, Carbides, and Phosphides The sulfides of the group IIA metals generally have the sodium chloride structure, but those of the group IA metals have the antifluorite structure because the ratio of anions to cations is 2. Solutions of the sulfides are basic as a result of the hydrolysis reaction. One preparation of the group IA and IIA sulfides involves the reaction of H 2 S with the metal hydroxides. Sulfides of the group IA and IIA metals can also be produced by reducing the sulfates with carbon at high temperature. 6/29/2020 137

138. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Lithopone, a commonly used pigment containing barium sulfate and zinc sulfide, is produced by the following reaction: Because Ca(OH) 2 is a base and H 2 S is an acid, the following reaction can be used to prepare CaS. Most nonmetallic elements will react with the group IA and IIA metals to give binary compounds. Heating the metals with nitrogen or phosphorus gives nitrides and phosphides of the metals. 6/29/2020 138

139. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS When the binary nitrides or phosphides react with water, basic solutions result because the anions undergo solvolysis reactions such as those represented by the equations Binary carbides are formed when the metals are heated strongly with carbon. The most important carbide of the group IIA metals is calcium carbide, CaC 2. This carbide is actually an acetylide because it contains the C 2 2-- ion and it reacts with water to produce acetylene 6/29/2020 139

140. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS The reaction between CaO and carbon (coke) at very high temperature produces CaC 2. Calcium acetylide is used in the manufacture of calcium cyanamide, CaCN 2, by the reaction of CaC 2 with N 2 at high temperature. Like the Haber process for the synthesis of ammonia, this reaction represents a way of converting elemental nitrogen into a compound (nitrogen fixation). Moreover, calcium cyanamide reacts with steam at high temperature to yield ammonia, 6/29/2020 140

141. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Calcium cyanamide is a constituent of fertilizers. Another cyanamide compound that has a number of significant uses is sodium cyanamide, which is prepared as shown below. Sodium amide is obtained by the reaction of ammonia with Na at 400°C. The reaction between sodium amide and carbon produces sodium cyanamide, which reacts with carbon to produce sodium cyanide. The major use of sodium cyanamide is in the production of sodium cyanide, a compound that is used extensively in preparing solutions for the electroplating of metals. Another use for NaCN is in extraction processes employed to separate gold and silver from ores as a result of their forming complexes with CN -. Sodium cyanide, an extremely toxic compound, is also used in the process known as casehardening of steel. In this process, the object to be hardened is heated and allowed to react with the cyanide to form a layer of metal carbide on the surface. 6/29/2020 141

142. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Carbonates, Nitrates, Sulfates, and Phosphates Some of the important compounds containing the group IA and IIA metals are the carbonates, nitrates, sulfates, and phosphates. Mineral trona as the source of sodium carbonate. Calcium carbonate is found in many forms that include chalk, calcite, aragonite, and marble, as well as in egg shells, coral, and seashells. In addition to its use as a building material, calcium phosphate is converted into fertilizers in enormous quantities. The carbonates, sulfates, nitrates, and phosphates of the group IA and IIA metals are important materials in inorganic chemistry. Some of the most important compounds of the group IA and IIA elements are organometallic compounds. 6/29/2020 142

143. C HEMICAL P ROPERTIES OF G ROUP IA AND G ROUP IIA E LEMENTS Carbonates, Nitrates, Sulfates, and Phosphates Magnesium is found as the carbonate in the mineral magnesite and as the silicate in the mineral olivine. Magnesium is also found as Epsom salts, MgSO 4.7H 2 O, which is used in solution for medicinal purposes. A mixed carbonate containing calcium and magnesium is dolomite, CaCO 3.MgCO 3, which is used in construction and in antacid tablets. Calcium is also found as CaSO 4.2H 2 O, gypsum. Beryl, which has the composition Be 3 Al 2 (SiO 3 ) 6, is one mineral that contains beryllium. If traces of chromium are present, the result is the green gemstone emerald. Among other sources, sodium and potassium are found as the nitrates, and a method for preparing nitric acid involves heating a nitrate with sulfuric acid. 6/29/2020 143

144. C HLORALKALI PROCESS It is an industrial process for the electrolysis of sodium chloride solution (brine). Depending on the method, several products produced along with hydrogen. If the products are separated, chlorine and sodium hydroxide (caustic soda) are the products; by mixing, sodium hypochlorite or sodium chlorate are produced, depending on the temperature. Higher temperatures are needed for the production of sodium chlorate instead of sodium hypochlorite. Industrial scale production began in 1892. When using calcium chloride or potassium chloride, the products contain calcium or potassium instead of sodium. Procedure There are three production methods; membrane, mercury and diaphragm cell. Chlorine and sodium hydroxide produced via the mercury-cell chloralkali process are contaminated with trace amounts of mercury. The membrane and diaphragm method use no mercury, but the sodium hydroxide contains chlorine, which must be removed. 6/29/2020 144

145. C HLORALKALI PROCESS Membrane cell method 6/29/2020 145

146. M EMBRANE CELL METHOD The most common chloralkali process involves the electrolysis of aqueous sodium chloride (a brine) in a membrane cell. Saturated brine is passed into the first chamber of the cell where the chloride ions are oxidised at the anode, losing electrons to become chlorine gas (A in figure): 2Cl – → Cl 2 + 2e – At the cathode, positive hydrogen ions pulled from water molecules are reduced by the electrons provided by the electrolytic current, to hydrogen gas, releasing hydroxide ions into the solution (C in figure): 2H 2 O + 2e – → H 2 + 2OH – The ion-permeable ion exchange membrane at the center of the cell allows the sodium ions (Na + ) to pass to the second chamber where they react with the hydroxide ions to produce caustic soda (NaOH) (B in figure). The overall reaction for the electrolysis of brine is thus: 2NaCl + 2H 2 O → Cl 2 + H 2 + 2NaOH 6/29/2020 146

147. M EMBRANE CELL METHOD At the cathode (C), water is reduced to hydroxide and hydrogen gas. The net process is the electrolysis of an aqueous solution of NaCl into industrially useful products sodium hydroxide (NaOH) and chlorine gas. A membrane cell is used to prevent the reaction between the chlorine and hydroxide ions. If this reaction were to occur the chlorine would be disproportionated to form chloride and hypochlorite ions: Cl 2 + 2OH – → Cl – + ClO – + H 2 O Above about 60 °C, chlorate can be formed: 3Cl 2 + 6OH – → 5Cl – + ClO 3 – + 3H 2 O 6/29/2020 147

148. M EMBRANE CELL METHOD Because of the corrosive nature of chlorine production, the anode (where the chlorine is formed) must be made from a non-reactive metal such as titanium, whereas the cathode (where hydroxide forms) can be made from a more easily oxidized metal such as nickel. In the membrane cell, the anode and cathode are separated by an ion-permeable membrane. Saturated brine is fed to the compartment with the anode (the anolyte). A DC current is passed through the cell and the NaCl splits into its constituent components. The membrane passes Na+ ions to the cathode compartment (catholyte), where it forms sodium hydroxide in solution. The membrane allows only positive ions to pass through to prevent the chlorine from mixing with the sodium hydroxide. The chloride ions are oxidised to chlorine gas at the anode, which is collected, purified and stored. Hydrogen gas and hydroxide ions are formed at the cathode. 6/29/2020 148

149. C HLORALKALI PROCESS Mercury cell (Castner–Kellner process) 6/29/2020 149

150. M ERCURY CELL (C ASTNER –K ELLNER PROCESS ) The apparatus shown is divided into two types of cells separated by slate walls. The first type, shown on the right and left of the diagram, uses an electrolyte of sodium chloride solution, a graphite anode (A), and a mercury cathode (M). The other type of cell, shown in the center of the diagram, uses an electrolyte of sodium hydroxide solution, a mercury anode (M), and an iron cathode (D). Note that the mercury electrode is shared between the three cells. This is achieved by having the walls separating the cells dip below the level of the electrolytes but still allow the mercury to flow beneath them. The reaction at anode (A) is: 2Cl – → Cl 2 + 2e – The chlorine gas that results vents at the top of the outside cells where it is collected as a byproduct of the process. The reaction at the mercury cathode in the outer cells is 2Na + + 2e – → 2Na 6/29/2020 150

151. M ERCURY CELL (C ASTNER –K ELLNER PROCESS ) The sodium metal formed by this reaction dissolves in the mercury to form an amalgam. The mercury conducts the current from the outside cells to the center cell. In addition, a rocking mechanism (B shown by fulcrum on the left and rotating eccentric on the right) agitates the mercury to transport the dissolved sodium metal from the outside cells to the center cell. The anode reaction in the center cell takes place at the interface between the mercury and the sodium hydroxide solution. 2Na (amalgam) → 2Na + + 2e – Finally at the iron cathode (D) of the center cell the reaction is 2H 2 O + 2e – → 2OH – + H 2 The net effect is that the concentration of sodium chloride in the outside cells decreases and the concentration of sodium hydroxide in the center cell increases. As the process commences some sodium hydroxide solution is withdrawn from center cell as output product and is replaced with water. Sodium chloride is added to the outside cells to replace what has been electrolyzed. 6/29/2020 151

152. C HLORALKALI PROCESS Diaphragm cell 6/29/2020 152

153. D IAPHRAGM CELL In the diaphragm cell process, there are two compartments separated by a permeable diaphragm, often made of asbestos fibers. Brine is introduced into the anode compartment and flows into the cathode compartment. Similarly to the Membrane Cell, chloride ions are oxidized at the anode to produce chlorine, and at the cathode, water is split into caustic soda and hydrogen. The diaphragm prevents the reaction of the caustic soda with the chlorine. Diluted caustic brine leaves the cell. The caustic soda must usually be concentrated to 50% and the salt removed. This is done using an evaporative process with about three tonnes of steam per tonne of caustic soda. The salt separated from the caustic brine can be used to saturate diluted brine. The chlorine contains oxygen and must often be purified by liquefaction and evaporation. 6/29/2020 153

154. D IAPHRAGM CELL Production of the chlorine Chlorine is produced at the titanium anode according to the equation: It is contaminated with some oxygen because of the reaction: The chlorine is purified by liquifying it under pressure. The oxygen stays as a gas when it is compressed at ordinary temperatures. Production of the hydrogen The hydrogen is produced at the steel cathode: Production of the sodium hydroxide A dilute solution of sodium hydroxide solution is also produced at the cathode (see above for the explanation of what happens at the cathode). It is highly contaminated with unchanged sodium chloride solution. The sodium hydroxide solution leaving the cell is concentrated by evaporation. During this process, most of the sodium chloride crystallizes out as solid salt. The salt can be separated, dissolved in water, and passed through the cell again. Even after concentration, the sodium hydroxide will still contain a small percentage of sodium chloride. 6/29/2020 154

155. E XTRACTION OF S ODIUM On industrial scale sodium metal is extracted by "Down's Process" which is based on the electrolysis of fused NaCl. Constructions of Down’s Cell: It consists of a rectangular container of steel, inner wall lined with firebricks. Anode is a graphite rod which projects centrally up through the base of the cell. Cathode is a ring of iron, which surrounds the anode. The anode and cathode are separated from each other by a cylindrical steel gauze diaphragm so that Na and Cl2 are kept apart. A bell like hood is submerged over the anode. Draw backs of Down’s method: Melting point of NaCl is 801 0 C. At this temperature molten NaCl and Na form a metallic fog in the container which is impossible to separate. Steps to overcome this difficulty: In order to over come this difficulty instead of only NaCl, a mixture of NaCl and CaCl2 is electrolyzed in down's cell. The melting point of this mixture is 600 0 C at which no metallic fog is formed. Composition of charge: NaCl = 42% and CaCl2 = 58% 6/29/2020 155

156. E XTRACTION OF S ODIUM Process: When an electric current is passed through the molten mixture of NaCl and CaCl 2, NaCl decomposes in to Na + and Cl - ion. Na + ions migrate towards cathode while Cl - ions towards the anode. The molten sodium collects in the cathode compartment where it rises to the top and is tapped off by a pipe. Chlorine is collected at the anode. 6/29/2020 156

157. E XTRACTION OF S ODIUM Electrochemical changes: Fused NaCl contains sodium and chloride ions. At cathode: Na + ions migrate to cathode where they are reduced to Na. 2Na + + 2e - ----------  2Na (Reduction) At anode: Cl - ions migrate to anode and oxidised to form chlorine gas. 2Cl - ---------------> Cl 2 + 2e - (Oxidation) Overall Reaction 2Na + + 2e - ---------  2Na 2Cl - -------  Cl 2 + 2e - __________________ 2Na + + 2Cl - -------  2Na + Cl 2 Question: During electrolysis Calcium is also obtained but it does not mix with Sodium. Explain. Answer: During electrolysis calcium is also obtained at cathode but sodium and calcium are separated from each other due difference in density. Density of Na is 0.67gm/cc and the density of Ca is much higher than that of Na i.e. 2.54gm/cc. That's why they do not mix with each other. 6/29/2020 157

158. E XTRACTION OF L ITHIUM Followings are the minerals of lithium. (i) Spodumene, LiAl(SiO 3 ) 2 – 6% Lithium (ii) Triphylite, (Li, Na) 2 PO 4 (Fe, Mn) 3 (PO 4 ) 2 – 4% Lithium (iii) Petalite, LiAl(Si 2 O 5 ) 4 – 2.7 – 3.7% Lithium (iv) Lepidolite, (Li, Na, K) 2 (SiO 3 ) 3 (FOH) 2 – 1.5% Lithium It involves the following steps: Preparation of Lithium chloride: The minerals are first of all converted into lithium chloride by any one of the following methods: i. Acid treatment method: The finely powdered silicate ore is first heated to about 1373 K to make it more friable and then with H 2 SO 4 at 523 K. The Li 2 SO 4 H 2 O thus formed is cooled, leached with water and then filtered to remove silica (SiO 2 ). The filtrate thus obtained is treated with a calculated amount of Na 2 CO 3 to precipitate aluminium and iron as carbonates which are filtered off. Excess of Na 2 CO 3 is then added to the filtrate to precipitate Li 2 CO 3. This is filtered and dissolved in HCl to obtain LiCl which is purified by extraction with alcohol. 6/29/2020 158

159. E XTRACTION OF L ITHIUM ii. Fusion method: The powdered silicate mineral is fused with CaCO 3 and the fused mass is extracted with HCl and filtered. The filtrate contains chlorides of Li, Al, Ca, Na and K whereas silicon is removed as insoluble residue. The filtrate is evaporated to dryness and the residue is extracted with pyridine in which only LiCl dissolves. Pyridine is distilled off while LiCl is left behind. The method discussed above may be summed up in the following flow-sheet. 6/29/2020 159

160. E XTRACTION OF L ITHIUM Electrolysis of Lithium chloride: A mixture of dry lithium chloride (55%) and potassium chloride (45%) is fused and electrolyzed in an electrolytic cell shown in the figure. 6/29/2020 160

161. E XTRACTION OF L ITHIUM Electrolysis of Lithium chloride: Potassium chloride is added to increase the conductivity of lithium chloride and to lower the fusion temperature. The cell is operated at a temperature of about 723 K and voltage of 8-9 volts is applied. As a result of electrolysis, the following reactions take place: LiCl ----------  Li + + Cl - At cathode: Li + + e - → Li At anode: 2Cl - - 2e - → Cl 2 Chlorine gas, a valuable by product liberated at the anode leaves the cell through the exit while molten lithium rises to the surface of the fused electrolytes and collects in the cast iron enclosure surrounding the cathode. The metal thus obtained is 99% pure and is preserved by keeping it wrapped in paraffin wax. It may be noted here that lithium being the lightest metal known (density = 0.534 g ) can not be stored in kerosene oil since it floats on the surface. 6/29/2020 161

162. S OLVAY (S ODA -A MMONIA ) P ROCESS The Solvay process results in soda ash (Na 2 CO 3 ) from brine (NaCl) and limestone (CaCO 3 ). The overall process is: 2NaCl + CaCO 3 → Na 2 CO 3 + CaCl 2 A simplified description can be given using the four stages of chemical reactions. In the first step, carbon dioxide (CO 2 ) passes through a concentrated aqueous solution of sodium chloride (NaCl) and ammonia (NH 3 ). NaCl + CO 2 + NH 3 + H 2 O → NaHCO 3 + NH 4 Cl (I) The carbon dioxide required for reaction (I) is produced by heating of the limestone at 950 - 1100 °C. The calcium carbonate (CaCO 3 ) in the limestone is partially converted to quicklime (calcium oxide (CaO)) and carbon dioxide: CaCO 3 → CO 2 + CaO (II) The sodium bicarbonate (NaHCO 3 ) that precipitates out in reaction (I) is filtered out from the hot ammonium chloride (NH 4 Cl) solution, and the solution is then reacted with the quicklime (calcium oxide (CaO)) left over from heating the limestone in step (II). 2NH 4 Cl + CaO → 2NH 3 + CaCl 2 + H 2 O (III) 6/29/2020 162

163. S OLVAY (S ODA -A MMONIA ) P ROCESS CaO makes a strong basic solution. The ammonia from reaction (III) is recycled back to the initial brine solution of reaction (I). The sodium bicarbonate (NaHCO3) precipitate from reaction (I) is then converted to the final product, sodium carbonate (washing soda: Na2CO3), by calcination (160-230 C), producing water and carbon dioxide as byproducts: 2 NaHCO3 → Na2CO3 + H2O + CO2 (IV) The carbon dioxide from step (IV) is recovered for re-use in step (I). When properly designed and operated, a Solvay plant can reclaim almost all its ammonia, and consumes only small amounts of additional ammonia to make up for losses. The only major inputs to the Solvay process are salt, limestone and thermal energy, and its only major byproduct is calcium chloride, which is sold as road salt. 6/29/2020 163

164. QNSQNS Discuss the cyclic nature of solvay process In what ways extraction of sodium differs from that of lithium. 6/29/2020 164

165. END OF LECTURE FOUR 11.06.2020 6/29/2020 165

166. TEST 1 WILL BE UP TO LECTURE FOUR IT WILL BE ON 25.06.2020, 06:00-07:30 AM ; AT CBSL CT 1 ANY CHANGES WILL BE COMMUNICATED 6/29/2020 166