The s-Block Elements

صفحه 1:
The s-Block Elements Chapter 39 

صفحه 2:
Members of the s-Block Elements ۲ IA Alkali metals IIA Alkaline Earth metals 

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Chapter summary * Characteristic properties of the s- block elements ¢ Variation in properties of the s-block elements * Variation in properties of the s-block compounds * Uses of compounds of the s-block elements 

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Characteristic properties of s-block elements * Metallic character * Low electronegativity * Basic oxides, hydroxides ¢ Ionic bond with fixed oxidation states * Characteristic flame colours * Weak tendency to from complex 

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Metallic character Tod ‏و و وه‎ ۵ 

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Electronegativity Group II Be 1.5 Mg 1.2 Ca 1.0 Sr 1.0 Ba 0.9 Ra 0.9 Group I 1۸ ‏لا‎ ‎Na 0.9 1 0.8 Rb 0.8 Cs 0.7 Fr 0 * Low nuclear attraction for outer electrons ۰ Highly electropositive * Small electronegativi ty 

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Basic oxides, hydroxides Hydroxid es Be(OH), Mg(OH), Ca(OH), Sr(OH), Ba(OH), Oxide BeO MgO CaO SrO BaO, Ba,O, Hydroxid es LiOH NaOH KOH RbOH Oxide Li,O Na,O, Na,O, K,O,, KO, Rb,O,, RbO, 

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Oxides, Peroxide, Superoxide Reaction with water: Oxide: 0» + H,O > 20H: Peroxide: 0, + 2H,O > H,O, + 20H Superoxide: 20, + 2H,O > 20H: + H,O, + O, a :0:.0: Li does not form peroxide or super oxide Li,O, > Li,O + % O, Peroxide ion Super oxide 

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Hydroxides —$§$<$§ — All are soluble, base strength increase. Group II hydroxide Be Mg Ca Sr _ Ba Solubility increase, from Amphoteric to basic, base strength increase 

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Predominantly ionic with fixed oxidation state Group I: Most electropositive metals. Low first I.E. and extremely high second I.E. Form predominantly ionic compounds with non-metals by losing one electron. Fixed oxidation state of +1. Group II: Electropositive metals. Low first and second I.E. but very high third LE.. Have a fixed oxidation state of +2. Be and Mg compounds possess some degree of covalent character. 

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Characteristic flame colours Nat Cl (g) > Na(g) + Cl(g) Na(g) — Na* (g) [Ne]3s! [Ne]3p! Na‘(g) — Na(g) + hv (589nm, yellow) 

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Flame test Ca brick red Sr blood red Ba apple green <> HCl(aq) sample 

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Weak tendency to form complex Complex formation is a common feature of d-block element. e.g. Co(NH,),°* :NH, s-block metal ions | have nolowenergy H;Nx_ | _/:NH, vacant orbital available ‏ا‎ ‎for bonding with lone pairs :NH,; of surrounding ligands, they rarely farm cramniavac 

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Check point 39-1 

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Variation in properties of elements ¢ Atomic radii * Ionization enthalpies ¢ Hydration enthalpies ٠ Melting points ¢ Reactions with oxygen, water, hydrogen and chlorine 

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Ra Atomic radii (nm) Li ه ده واه ب-اه یاو نب دز ۳ ‎Ny NU bh‏ هم ‎By of af‏ إمم N N Be Mg Ca Sr Ba 

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Ionization Enthapy 3rd LE. 14800 7740 4940 4120 3390 2nd LE. 1760 1450 1150 1060 966 1st LE. 900 736 590 548 502 2nd 1.4 Group Be Mg Ca Sr Ba 7 4 3 2 2 1st LE. 519 494 418 402 376 

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Ionization Enthalpy 2000 ae 1500 nd IE 1000 Ca*—__ Bat 500 ‏تج‎ 1st LE. 

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Ionization Enthalpy Group I 1. Have generally low 1*' I.E. as it is well shielded from the nucleus by inner shells. 2. Removal of a 2" electron is much more difficult because it involves the removal of inner shell electron. 3. LE. decreases as the group is descended. As atomic radius increases, the outer e is further away from the well- 

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Ionization Enthalpy Group IT 1. Have low 1st and 2nd IE. 2. Removal of the 3™ electron is much more difficult as it involves the loss of an inner shell electron. 3. IE decrease as the group is descended. 4. IE of the group II is generally higher than group I. 

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Hydration Enthalpy M*(g) + aqueous > M*(aq) + heat -600 we 

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Hydration Enthalpy -2250 -600) -2000 -1750 -300} -1500) — 8 8 a ee Lit Na* K* Rb* Cs* Be** Mg? Ca®* Sr* Ba®* 

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Hydration Enthalpy sneral trends: On going down both groups, hydration enthalpy decreases. (As the ions get larger, the charge density of the ions decreases, the electrostatic attraction between ions and water molecules gets smaller.) . Group 2 ions have hydration enthalpies higher than group 1. ( Group 2 cations are doubly charged and have smaller sizes) 

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Variation in Melting Points 

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Variation in Melting Points Strength of metallic bond depends on: 1. Ionic radius 2. Number of e contributed to the electron sea per ator 3. Crystal lattice structure Note: The exceptionally high m.p. of calcium is due to contribution of d-orbital participation of metallic bonding. 

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Variation in Melting Points Group |Structu II re Be ‏سا‎ ‎Mg 1162 Ca CCP, Sr CCP. Ba B.C.C. 

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Reactions with oxygen S-block elements are strong reducing agents. Their reducing power increases down both groups. (As the atomic size increases, it becomes easier to remove the outermost electron) S-block elements reacts readily with oxygen. Except Be and Mg, they have to be stored under liquid paraffin to prevent contact with the atmosphere. 

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Reactions with oxygen Normal | Peroxide |Superoxi Oxide de Structur we De ‏موی به‎ ae e 3 :0-0: :0:.0: Formed |Li and Na and K, Rb, Cs by Group II |Ba 

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Check point 39-2 

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Reaction with water M(s) > M+(aq) + & H,O(1) + e — OH(aq) + % H,(g) Li -3.05 volt Na -2.71 1 3 Be -1.85 volt Rb -2.99 Mg -2.38 Cs -3.20 Ca -2.87 Sr -2.89 Ba -2.90 Energetic vs. Kinetic Factor 

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Reaction with hydrogen All the s-block elements except Be react directly with hydrogen. 2Na(s) + H,(g) - 2NaH(s) Ca(s) + H,(g) > CaH,(s) The reactivity increases down the group. Only BeH, and MgH, are covalent, others are ionic. 

صفحه 32:
Reaction with chlorine All the s-block metals react directly with chlorine to produce chloride. All group I chlorides are ionic. BeCl, is essentially covalent, with comparatively low m.p. The lower members in group II form essentially ionic chlorides, with Mg having intermediate properties. 

صفحه 33:
Check point 39-3 Although lithium has highly negative E®, it only reacts slowly with water. This illustrates the importance of the role of kinetic factors in determining the rate of a chemical reaction. Lithium has a higher m.p., this increases the activation energy required for dissolution in aqueous solution. It does not melt during the reaction as Na and K do, and thus it has a smaller area of contact with water. 

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Variation in properties of the compounds * Reactions of oxides and hydroxides * Reactions of chlorides * Reactions of hydrides * Relative thermal stability of carbonates and hydroxides * Relative solubility of sulphate(VI and hydroxde 

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Reactions of oxides and hydroxides 1. All group I oxides reacts with water to form hydroxides Oxide: O> + H,O > 20H: Peroxide: 0,2 + 2H,O > H,O, + 20H ‎WAL 8 ATTA 7 ATI. +‏ حك عع سويح ‎2. All group I oxides/hydroxides are basic and the basicity increases down the group. 

صفحه 36:
Reactions of oxides and hydroxides 

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Reactions of chlorides 1. All group I chlorides are ionic and readily soluble in water. No hydrolysis occurs. 2. Group II chlorides show some degree of covalent character. Beryllium chloride is covalent and hydrolysis to form Be(OH),(s) and HCl(aq). Magnesium chloride is intermediate, it dissolves and hydrolysis slightly. Other group II chlorides just dissolve without hydrolysis. 

صفحه 38:
Reactions of hydrides They all react readily with water to give the metal hydroxide and hydrogen due to the strong basic property of the hydride ion, H: H:(s)+ H,O(1) > H,(g)+ OH (aq) Hydride ions are also good reducing agent. They can be used to prepare complex hydrides such as LiAlH, and NaBH, which are used to reduce C=O in organic chemistry. 

صفحه 39:
Thermal Stability 

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Thermal Stability of carbonates Li,CO, > Li,O + CO, (at 700°C) All other group I carbonates are stable at ~800°C BeCO, > BeO + CO, (at 100°C) MgCO, > MgO + CO, (at 540°C) CaCO, 0620 + CO, (at 900°C) SrCO,>SrO+CO, (at 1290°C) BaCO,— BaO + CO, (at 1360°C) 

صفحه 41:
Thermal Stability of hydroxides All group I hydroxides are stable except LiOH at Bunsen temperature. Be(OH),(s) > BeO(s) + H,O(g) AH = +54 kJ/mol Mg(OH),(s) > MgO(s) + H,O(g) AH = +81 kJ/mol Ca(OH),(s) > CaO(s) + H,O(g) AH = +109 kJ/mol Sr(OH),(s) > SrO(s) + H,O(g) AH = +127 kJ/mol Ba(OH),(s) > BaO(s) + H,O(g) AH = +146 kJ/mol 

صفحه 42:
Thermal stability 1. Carbonates and hydroxides of Group I metals are as a whole more stable than those of Group II. 2. Thermal stability increases on descending the group. 3. Lithium often follow the pattern of Group II rather than Group I. This is an example of the diagonal relationship. 

صفحه 43:
Explanation of Thermal Stability . Charge of the ions . Size of the ions . Compounds are more stable if the charge increases and size decreases. . For compounds with large polarizable anions, thermal stability is affected by the polarizing power of the cations. جر رحج تن 

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Explanation of Thermal Stability Decréasin Increasing polarizing stability pow 

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Explanation of Thermal Stability 9 _ >“ و00 + 07*0۶2 مت کت +92 ie OH Mgt |? ___. Mg?* 0? + H,O ‏تم‎ 

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Explanation of Thermal lan Stability ( Ww) ‏ووه ع‎ ‏یم‎ 

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Relative solubility of Group II hydroxides hydroxides wn the group. Solubility increases Solubility / mol per 100g water 0.020 x 10% 1.5x 10° 3.4x 103 15x 108 Compou nd Mg(OH), Ca(OH), Sr(OH), Ba(OH), 

صفحه 48:
Solubility of Group II sulphates Compou | Solubility / mol per nd 100g water MgSO, 3600 x 10% 2 Solubility of sulphates CaSO, 11x 104 increases up the group. SrSO, 0.62 x 104 BaSO, 0.009 x 10+ 

صفحه 49:
Explanation of solubility aque 1۳۹9 ‏ره‎ + X(aq) FT sotation -AH jattice AH iyaration M*(g) + X(g) AX sotution = ‏كلفد‎ pattie + AH pydration 

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Explanation of solubility AG sotution = “AH iattin + MAL ydration 

صفحه 51:
Explanation of solubility ~AH jattic: + AH hydration AH solution For Group II sulpha than the anions. T| not cause a signifi to 1/(r, + 1). However, the chai / AH jyaration (PrOpOrti] 55 exothermic, and tl descending the Gr 

صفحه 52:
Explanation of solubility AH ~AH jattic + MAL pydration solution = 3. For the smaller size anions, OH. Down the Group, less e| = break the lattice as the ‏کت‎ ۱ in| 024 smaller due to the larg 0 As a result, AH ‏مم © وووون.‎ and the solubility incre Mg(OH), Sr(OH), 

صفحه 53:
Check point 39-4 

صفحه 54:
Uses of s-block compounds * Sodium carbonate - Manufacture of glass - Water softening - Paper industry * Sodium hydrocarbonate - Baking powder - Soft drink 

صفحه 55:
Uses of s-block compounds ¢ Sodium hydroxide - Manufacture of soaps, dyes, paper and drugs - To make rayon and important chemicals ¢ Magnesium hydroxide - Milk of magnesia, an antacid * Calcium hydroxide - To neutralize acids in waste water treatment ¢ Strontium compound - Fireworks, persistent intense red flame 

The s-Block Elements Chapter 39 IA Li Members of the s-Block Elements IIA Be Na Mg K Ca Rb Sr Cs Ba Fr Ra IA Alkali metals IIA Alkaline Earth metals Chapter summary • Characteristic properties of the sblock elements • Variation in properties of the s-block elements • Variation in properties of the s-block compounds • Uses of compounds of the s-block elements Characteristic properties of s-block elements • Metallic character • Low electronegativity • Basic oxides, hydroxides • Ionic bond with fixed oxidation states • Characteristic flame colours • Weak tendency to from complex Metallic character • High tendency to lose e- to form positive ions • Metallic character increases down both groups Electronegativity • Low nuclear attraction for outer electrons • Highly electropositive • Small electronegativi ty Group I Group II Li 1.0 Be 1.5 Na 0.9 Mg 1.2 K 0.8 Ca 1.0 Rb 0.8 Sr 1.0 Cs 0.7 Ba 0.9 Fr 0.7 Ra 0.9 Basic oxides, hydroxides Oxide Hydroxid es LiOH Oxide BeO Hydroxid es Be(OH)2 Na2O, Na2O2 NaOH MgO Mg(OH)2 CaO Ca(OH)2 K2O2, KO2 KOH SrO Sr(OH)2 Rb2O2, RbO2 RbOH BaO, Ba2O2 Ba(OH)2 Li2O Oxides, Peroxide, Superoxide Reaction with water: Oxide: O2- + H2O  2OHPeroxide: O22- + 2H2O  H2O2 + 2OHSuperoxide: 2O2- + 2H2O  2OH- + H2O2 + O2 .. .. 2:O:O: .. .. Peroxide ion . .:O:.O: .. .. Li does not form peroxide or super oxide Super oxide Li2O2  Li2O + ½ O2 Hydroxides Group I hydroxides Li Na K Rb Cs All are soluble, base strength increase. Group II hydroxide Be Mg Ca Sr Ba Solubility increase, from Amphoteric to basic, base strength increase Predominantly ionic with fixed oxidation state Group I: Most electropositive metals. Low first I.E. and extremely high second I.E. Form predominantly ionic compounds with non-metals by losing one electron. Fixed oxidation state of +1. Group II: Electropositive metals. Low first and second I.E. but very high third I.E.. Have a fixed oxidation state of +2. Be and Mg compounds possess some degree of covalent character. Characteristic flame colours Na+ Cl- (g)  Na (g) + Cl (g) Na(g)  Na* (g) [Ne]3s1 [Ne]3p1 Na*(g)  Na(g) + h (589nm, yellow) Flame test Li Na K Rb Cs HCl(aq) deep red Ca brick red yellow Sr blood red lilac Ba apple green bluish red blue sample Weak tendency to form complex Complex formation is a common feature of d-block element. e.g. Co(NH3)63+ s-block metal ions have no low energy vacant orbital available for bonding with lone pairs of surrounding ligands, they rarely :NH3 H3N: H3N: :NH3 Co :NH3 :NH3 Check point 39-1 Variation in properties of elements • Atomic radii • Ionization enthalpies • Hydration enthalpies • Melting points • Reactions with oxygen, water, hydrogen and chlorine Atomic radii (nm) Li Na 0.15 Be 2 0.11 2 0.18 Mg 6 0.16 0 Fr K 0.23 Ca 1 0.19 7 Li Rb 0.24 Sr 4 0.21 5 Be Cs 0.26 Ba 2 0.21 7 Fr 0.27 Ra 0.22 Ra Ionization Enthapy Group 1st I I.E. Li 519 Na 494 K 418 Rb 402 Cs 376 2nd I.E.Group 1st I I.E. 7300 Be 4560 Mg 3070 Ca 2370 Sr 2420 Ba 2nd I.E. 3rd I.E. 900 1760 14800 736 1450 7740 590 1150 4940 548 1060 4120 502 966 3390 Ionization Enthalpy 1st I.E. 2000 600 500 400 300 Li Na K Be+ 1500 Rb Cs 1000 500 2nd IE Ca+ Be Ca 1st IE Ba+ Ba Ionization Enthalpy Group I 1. Have generally low 1st I.E. as it is well shielded from the nucleus by inner shells. 2. Removal of a 2nd electron is much more difficult because it involves the removal of inner shell electron. 3. I.E. decreases as the group is descended. As atomic radius increases, the outer e is further away from the well- Ionization Enthalpy Group II 1. Have low 1st and 2nd IE. 2. Removal of the 3rd electron is much more difficult as it involves the loss of an inner shell electron. 3. IE decrease as the group is descended. 4. IE of the group II is generally higher than group I. Hydration Enthalpy M+(g) + aqueous  M+(aq) + heat -600 M+ -300 Li+ Na+ K+ Rb+ Cs+ Hydration Enthalpy -2250 -600 -2000 -1750 -300 -1500 Li+ Na+ K+ Rb+ Cs+ Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Hydration Enthalpy eneral trends: On going down both groups, hydration enthalpy decreases. (As the ions get larger, the charge density of the ions decreases, the electrostatic attraction between ions and water molecules gets smaller.) 2. Group 2 ions have hydration enthalpies higher than group 1. ( Group 2 cations are doubly charged and have smaller sizes) Variation in Melting Points 1250 Be 1000 Ca Sr 750 Ba Mg 500 250 Li Na 10 50 K Rb 20 60 30 Cs 40 Variation in Melting Points Strength of metallic bond depends on: 1. Ionic radius 2. Number of e- contributed to the electron sea per atom 3. Crystal lattice structure Note: The exceptionally high m.p. of calcium is due to contribution of d-orbital participation of metallic bonding. Variation in Melting Points Group I Structu Group re II Li B.C.C. Be Na B.C.C. Mg K Rb Cs B.C.C. B.C.C. B.C.C. Ca Sr Ba Structu re H.C.P. H.C.P. C.C.P. C.C.P. B.C.C. Reactions with oxygen S-block elements are strong reducing agents. Their reducing power increases down both groups. (As the atomic size increases, it becomes easier to remove the outermost electron) S-block elements reacts readily with oxygen. Except Be and Mg, they have to be stored under liquid paraffin to prevent contact with the atmosphere. Reactions with oxygen Normal Oxide Structur e Formed by .. 2:O: .. Li and Group II Peroxide Superoxi de .. .. 2:O-O: .. .. Na and Ba . .:O:.O: .. .. K, Rb, Cs Check point 39-2 Reaction with water M(s)  M+(aq) + eH2O(l) + e-  OH-(aq) + ½ H2(g) Li Na K Rb Cs -3.05 volt -2.71 Be -2.93 Mg -2.99 Ca -3.20 Sr Ba -1.85 volt -2.38 -2.87 -2.89 -2.90 Energetic vs. Kinetic Factor Reaction with hydrogen All the s-block elements except Be react directly with hydrogen. 2Na(s) + H2(g)  2NaH(s) Ca(s) + H2(g)  CaH2(s) The reactivity increases down the group. Only BeH2 and MgH2 are covalent, others are ionic. Reaction with chlorine All the s-block metals react directly with chlorine to produce chloride. All group I chlorides are ionic. BeCl2 is essentially covalent, with comparatively low m.p. The lower members in group II form essentially ionic chlorides, with Mg having intermediate properties. Check point 39-3 Although lithium has highly negative Eo, it only reacts slowly with water. This illustrates the importance of the role of kinetic factors in determining the rate of a chemical reaction. Lithium has a higher m.p., this increases the activation energy required for dissolution in aqueous solution. It does not melt during the reaction as Na and K do, and thus it has a smaller area of contact with water. Variation in properties of the compounds • Reactions of oxides and hydroxides • Reactions of chlorides • Reactions of hydrides • Relative thermal stability of carbonates and hydroxides • Relative solubility of sulphate(VI) and hydroxde Reactions of oxides and hydroxides 1. All group I oxides reacts with water to form hydroxides Oxide: O2- + H2O  2OHPeroxide: O22- + 2H2O  H2O2 + 2OHSuperoxide: 2O2- + 2H2O  2OH- + 2. All group I oxides/hydroxides are basic and the H2O2 + O2 basicity increases down the group. Reactions of oxides and hydroxides 3. Group II oxides/hydroxides are generally less basic than Group I. Beryllium oxide/hydroxide are amphoteric. Reactions of chlorides 1. All group I chlorides are ionic and readily soluble in water. No hydrolysis occurs. 2. Group II chlorides show some degree of covalent character. Beryllium chloride is covalent and hydrolysis to form Be(OH)2(s) and HCl(aq). Magnesium chloride is intermediate, it dissolves and hydrolysis slightly. Other group II chlorides just dissolve without hydrolysis. Reactions of hydrides They all react readily with water to give the metal hydroxide and hydrogen due to the strong basic property of the hydride ion, H:H:-(s)+ H2O(l)  H2(g)+ OH-(aq) Hydride ions are also good reducing agent. They can be used to prepare complex hydrides such as LiAlH4 and NaBH4 which are used to reduce C=O in organic chemistry. Thermal Stability Thermal stability refers to decomposition of the compound on heating. Increased thermal stability means a higher temperature is needed to decompose the compound. Thermal Stability of carbonates Li2CO3  Li2O + CO2 ( at 700oC) All other group I carbonates are stable at ~800oC BeCO3  BeO + CO2 MgCO3  MgO + CO2 CaCO3  CaO + CO2 SrCO3  SrO + CO2 BaCO3  BaO + CO2 ( at 100oC) ( at 540oC) ( at 900oC) ( at 1290oC) ( at 1360oC) Thermal Stability of hydroxides All group I hydroxides are stable except LiOH at Bunsen temperature. Be(OH)2(s)  BeO(s) + H2O(g) Mg(OH)2(s)  MgO(s) + H2O(g) Ca(OH)2(s)  CaO(s) + H2O(g) Sr(OH)2(s)  SrO(s) + H2O(g) Ba(OH)2(s)  BaO(s) + H2O(g) H = +54 kJ/mol H = +81 kJ/mol H = +109 kJ/mol H = +127 kJ/mol H = +146 kJ/mol Thermal stability 1. Carbonates and hydroxides of Group I metals are as a whole more stable than those of Group II. 2. Thermal stability increases on descending the group. 3. Lithium often follow the pattern of Group II rather than Group I. This is an example of the diagonal relationship. Explanation of Thermal Stability 1. Charge of the ions 2. Size of the ions 3. Compounds are more stable if the charge increases and size decreases. 4. For compounds with large polarizable anions, thermal stability is affected by the polarizing power of the cations. Explanation of Thermal Stability + Decreasing polarizing + power + - - - Increasing stability Explanation of Thermal Stability O Mg2+ - :O C O:- :O H Mg2+ O2- + CO2 - Mg2+ - :O H Mg2+ O2- + H2O Explanation of Thermal Stability MgCO3 MgO BaO MgO BaCO3 BaO Relative solubility of Group II hydroxides Compou nd Solubility / mol per 100g water Mg(OH)2 0.020 x 10-3 Ca(OH)2 1.5 x 10-3 Sr(OH)2 3.4 x 10-3 Ba(OH)2 15 x 10-3 Solubility of hydroxides increases down the group. Solubility of Group II sulphates Compou nd Solubility / mol per 100g water MgSO4 3600 x 10-4 CaSO4 11 x 10-4 SrSO4 0.62 x 10-4 BaSO4 0.009 x 10-4 Solubility of sulphates increases up the group. Explanation of solubility aqueous MX(s) M+(aq) + X-(aq) H solution -H H lattice hydration M+(g) + X-(g) H solution = -H lattice + H hydration Explanation of solubility 1. Group I compounds are more soluble than Group II because the metal ions have smaller charges and larger sizes. H lattice is smaller, and H solution is more exothermic. H solution = -H lattice + H hydration Explanation of solubility H solution = -H lattice + H hydration For Group II sulphates, the cations are much smaller than the anions. The changing in size of cations does not cause a significant change in H lattice (proportional 22SO SO 4 4 to 1/(r+ + r-). However, the changing in size of cations does cause H hydration (proportional to 1/r+ and 1/r-) to become less exothermic, and the solubility decreases when descending the Group. MgSO4 SrSO4 Explanation of solubility H solution = -H lattice + H hydration 3. For the smaller size anions, OH-. Down the Group, less enthalpy is required to break the lattice as the size of cation increases. However the change in H solution is comparatively smaller due to the large value of 1/r- . As a result, H solution becomes more exothermic and the solubility increases down the Group. Mg(OH)2 Sr(OH)2 Check point 39-4 Uses of s-block compounds • Sodium carbonate – Manufacture of glass – Water softening – Paper industry • Sodium hydrocarbonate – Baking powder – Soft drink Uses of s-block compounds • Sodium hydroxide – Manufacture of soaps, dyes, paper and drugs – To make rayon and important chemicals • Magnesium hydroxide – Milk of magnesia, an antacid • Calcium hydroxide – To neutralize acids in waste water treatment • Strontium compound – Fireworks, persistent intense red flame