The s-Block Elements

The s-Block Elements

اسلاید 1: The s-Block ElementsChapter 39

اسلاید 2: Members of the s-Block ElementsLiBeNaKRbCsFrMgCaSrRaBaIA IIAIA Alkali metalsIIA Alkaline Earth metals

اسلاید 3: Chapter summaryCharacteristic properties of the s-block elementsVariation in properties of the s-block elementsVariation in properties of the s-block compoundsUses of compounds of the s-block elements

اسلاید 4: Characteristic properties of s-block elementsMetallic characterLow electronegativityBasic oxides, hydroxidesIonic bond with fixed oxidation statesCharacteristic flame coloursWeak tendency to from complex

اسلاید 5: Metallic characterHigh tendency to lose e- to form positive ionsMetallic character increases down both groups

اسلاید 6: ElectronegativityLow nuclear attraction for outer electronsHighly electropositiveSmall electronegativityGroup IGroup IILi 1.0Be 1.5Na 0.9Mg 1.2K 0.8Ca 1.0Rb 0.8Sr 1.0Cs 0.7Ba 0.9Fr 0.7Ra 0.9

اسلاید 7: Basic oxides, hydroxidesOxideHydroxidesLi2OLiOHNa2O, Na2O2NaOHK2O2, KO2KOHRb2O2, RbO2RbOHCs2O2, CsO2CsOHOxideHydroxidesBeOBe(OH)2MgOMg(OH)2CaOCa(OH)2SrOSr(OH)2BaO, Ba2O2Ba(OH)2

اسلاید 8: Oxides, Peroxide, SuperoxideReaction with water:Oxide: O2- + H2O  2OH-Peroxide: O22- + 2H2O  H2O2 + 2OH-Superoxide: 2O2- + 2H2O  2OH- + H2O2 + O2 .. .. 2-:O:O: .. ..Peroxide ion . . -:O:.O: .. ..Super oxideLi does not formperoxide or super oxideLi2O2  Li2O + ½ O2

اسلاید 9: HydroxidesGroup Ihydroxides Li Na K Rb CsAll are soluble, base strength increase.Group IIhydroxide Be Mg Ca Sr BaSolubility increase, fromAmphoteric to basic, base strength increase

اسلاید 10: Predominantly ionic with fixed oxidation stateGroup 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.

اسلاید 11: Characteristic flame coloursNa+ Cl- (g)  Na (g) + Cl (g)Na(g)  Na* (g)[Ne]3s1 [Ne]3p1Na*(g)  Na(g) + h (589nm, yellow)

اسلاید 12: Flame testHCl(aq)sampleLi deep redNa yellowK lilacRb bluish redCs blueCa brick redSr blood redBa apple green

اسلاید 13: Weak tendency to form complexs-block metal ions have no low energy vacantorbital available for bonding with lone pairsof surrounding ligands, they rarely form complexes.Complex formation is a common feature of d-blockelement. e.g. Co(NH3)63+Co:NH3:NH3 :NH3:NH3H3N:H3N:

اسلاید 14: Check point 39-1

اسلاید 15: Variation in properties of elementsAtomic radiiIonization enthalpiesHydration enthalpiesMelting pointsReactions with oxygen, water, hydrogen and chlorine

اسلاید 16: Atomic radii (nm)Li0.152Be0.112Na0.186Mg0.160K0.231Ca0.197Rb0.244Sr0.215Cs0.262Ba0.217Fr0.270Ra0.220LiFrBeRa

اسلاید 17: Ionization EnthapyGroup I1st I.E.2nd I.E.Li5197300Na4944560K4183070Rb4022370Cs3762420Group I1st I.E.2nd I.E.3rd I.E.Be900176014800Mg73614507740Ca59011504940Sr54810604120Ba5029663390

اسلاید 18: Ionization EnthalpyLiNaKRbCs1st I.E.300400500600500100015002000BeCaBaBe+Ca+Ba+1st IE2nd IE

اسلاید 19: Ionization EnthalpyGroup IHave 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-shielded nucleus.

اسلاید 20: Ionization EnthalpyGroup IIHave low 1st and 2nd IE.Removal of the 3rd electron is much more difficult as it involves the loss of an inner shell electron.IE decrease as the group is descended.IE of the group II is generally higher than group I.

اسلاید 21: Hydration EnthalpyM+(g) + aqueous  M+(aq) + heatM+-600-300Li+ Na+ K+ Rb+ Cs+

اسلاید 22: Hydration Enthalpy-600-300Li+ Na+ K+ Rb+ Cs+Be2+ Mg2+ Ca2+ Sr2+ Ba2+ -2250-2000-1750-1500

اسلاید 23: Hydration EnthalpyGeneral 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)

اسلاید 24: Variation in Melting Points10 20 30 40 50 6025050075010001250BeMgCaSrBaLiNaKRbCs

اسلاید 25: Variation in Melting PointsStrength of metallic bond depends on:Ionic radiusNumber of e- contributed to the electron sea per atomCrystal lattice structureNote: The exceptionally high m.p. of calciumis due to contribution of d-orbital participationof metallic bonding.

اسلاید 26: Variation in Melting PointsGroup IStructureGroup IIStructureLiB.C.C.BeH.C.P.NaB.C.C.MgH.C.P.KB.C.C.CaC.C.P.RbB.C.C.SrC.C.P.CsB.C.C.BaB.C.C.

اسلاید 27: Reactions with oxygenS-block elements are strong reducing agents.Their reducing power increases down both groups.(As the atomic size increases, it becomes easier toremove the outermost electron)S-block elements reacts readily with oxygen. Except Be and Mg, they have to be stored underliquid paraffin to prevent contact with the atmosphere.

اسلاید 28: Reactions with oxygenNormal OxidePeroxideSuperoxideStructureFormed byLi and Group IINa and BaK, Rb, Cs .. .. 2-:O-O: .. .. .. 2-:O: .. . . -:O:.O: .. ..

اسلاید 29: Check point 39-2

اسلاید 30: Reaction with waterM(s)  M+(aq) + e-H2O(l) + e-  OH-(aq) + ½ H2(g)Li -3.05 voltNa -2.71K -2.93Rb -2.99Cs -3.20Be -1.85 voltMg -2.38Ca -2.87Sr -2.89Ba -2.90Energetic vs. Kinetic Factor

اسلاید 31: Reaction with hydrogenAll the s-block elements except Be react directly withhydrogen. 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.

اسلاید 32: Reaction with chlorineAll the s-block metals react directly with chlorineto produce chloride.All group I chlorides are ionic.BeCl2 is essentially covalent, with comparatively lowm.p.The lower members in group II form essentially ionicchlorides, with Mg having intermediate properties.

اسلاید 33: Check point 39-3Although lithium has highly negative Eo, it onlyreacts slowly with water. This illustrates the importanceof the role of kinetic factors in determining the rateof a chemical reaction.Lithium has a higher m.p., this increases the activationenergy required for dissolution in aqueous solution.It does not melt during the reaction as Na and K do, andthus it has a smaller area of contact with water.

اسلاید 34: Variation in properties of the compoundsReactions of oxides and hydroxidesReactions of chloridesReactions of hydridesRelative thermal stability of carbonates and hydroxidesRelative solubility of sulphate(VI) and hydroxde

اسلاید 35: Reactions of oxides and hydroxidesAll group I oxides reacts with water to form hydroxides Oxide: O2- + H2O  2OH- Peroxide: O22- + 2H2O  H2O2 + 2OH- Superoxide: 2O2- + 2H2O  2OH- + H2O2 + O2All group I oxides/hydroxides are basic and the basicity increases down the group.

اسلاید 36: Reactions of oxides and hydroxidesGroup II oxides/hydroxides are generally less basic than Group I. Beryllium oxide/hydroxide are amphoteric.

اسلاید 37: Reactions of chloridesAll group I chlorides are ionic and readily soluble in water. No hydrolysis occurs. 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.

اسلاید 38: Reactions of hydridesThey all react readily with water to give themetal 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 hydridessuch as LiAlH4 and NaBH4 which are used toreduce C=O in organic chemistry.

اسلاید 39: Thermal StabilityThermal stability refers to decomposition of thecompound on heating. Increased thermal stabilitymeans a higher temperature is needed to decomposethe compound.

اسلاید 40: Thermal Stability of carbonatesLi2CO3  Li2O + CO2 ( at 700oC)All other group I carbonates are stable at ~800oCBeCO3  BeO + CO2 ( at 100oC)MgCO3  MgO + CO2 ( at 540oC)CaCO3  CaO + CO2 ( at 900oC)SrCO3  SrO + CO2 ( at 1290oC)BaCO3  BaO + CO2 ( at 1360oC)

اسلاید 41: Thermal Stability of hydroxidesAll group I hydroxides are stable except LiOHat Bunsen temperature.Be(OH)2(s)  BeO(s) + H2O(g) H = +54 kJ/molMg(OH)2(s)  MgO(s) + H2O(g) H = +81 kJ/molCa(OH)2(s)  CaO(s) + H2O(g) H = +109 kJ/molSr(OH)2(s)  SrO(s) + H2O(g) H = +127 kJ/molBa(OH)2(s)  BaO(s) + H2O(g) H = +146 kJ/mol

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

اسلاید 43: Explanation of Thermal StabilityCharge of the ionsSize of the ionsCompounds 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.

اسلاید 44: Explanation of Thermal Stability+++---DecreasingpolarizingpowerIncreasingstability

اسلاید 45: Explanation of Thermal StabilityMg2+COO:-- :OMg2+ O2- + CO2Mg2+Mg2+ O2- + H2O-:O-:OHH

اسلاید 46: Explanation of Thermal StabilityMgCO3MgOBaCO3BaOMgOBaO

اسلاید 47: Relative solubility of Group II hydroxidesCompoundSolubility / mol per 100g waterMg(OH)20.020 x 10-3Ca(OH)21.5 x 10-3Sr(OH)23.4 x 10-3Ba(OH)215 x 10-3Solubility of hydroxidesincreases down the group.

اسلاید 48: Solubility of Group II sulphatesCompoundSolubility / mol per 100g waterMgSO43600 x 10-4CaSO411 x 10-4SrSO40.62 x 10-4BaSO40.009 x 10-4Solubility of sulphatesincreases up the group.

اسلاید 49: Explanation of solubilityMX(s)aqueousH solutionM+(aq) + X-(aq)M+(g) + X-(g)H hydration-H latticeH solution-H latticeH hydration=+

اسلاید 50: Explanation of solubilityGroup 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=+

اسلاید 51: Explanation of solubilityFor 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 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.H solution-H latticeH hydration=+SO42-MgSO4SO42-SrSO4

اسلاید 52: Explanation of solubilityFor 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.H solution-H latticeH hydration=+Mg(OH)2Sr(OH)2

اسلاید 53: Check point 39-4

اسلاید 54: Uses of s-block compoundsSodium carbonateManufacture of glassWater softeningPaper industrySodium hydrocarbonateBaking powderSoft drink

اسلاید 55: Uses of s-block compoundsSodium hydroxideManufacture of soaps, dyes, paper and drugsTo make rayon and important chemicalsMagnesium hydroxideMilk of magnesia, an antacidCalcium hydroxideTo neutralize acids in waste water treatmentStrontium compoundFireworks, persistent intense red flame