无机化学课件7group iiia

1、Group IIIA, (Group 13)Boron, Aluminum, Gallium, Indium, ThalliumGROUP 3A The elements: B, Al, Ga, In, Tl; all metals except boron valence electron configuration, ns2 np1 so the +3 oxidation state is expected to be most stable Gallium:- unusually low melting point, 303 K long liquid range; 303 2477 K

2、used in transistors and high T thermometersThe lower oxidation states e more important down the group- ionic Tl exist primarily in the +1 oxidation state Related to the inert pair effect the fact that the heavier elements lose their np electrons but nottheir ns electrons Lower oxidation state oxides

3、 are more basicBORON Boron shows nonmetallic properties all boroncompounds are covalent There are no ionic B3+ compounds, c.f. Mg2+ and Li+.Sources Ulexite硼钠钙石: NaCaB5O6(OH)6.5H2OBorax硼砂: Na2B4O5(OH)4.8H2OColmanite: Ca2B3O4(OH)3.2H2OKenite: Na2B4O5(OH)4.2H2OStructures of ElementsAl-Tl are all metals

4、, as expected from their R/I values.Boron would like to be covalent, but it wants to make 5 bonds to achieve a Lewis octet.It only has 4 orbitals though (1x2s+3x2p)B gets around its problem by forming delocalised polyhedra.Very important in B chemistry. AAA Halidesthe boron halides are highly reacti

5、veThey are volatile, covalent compounds2B + 3X2 2BX3X = F, Cl, Br, IBF3 and BCl3 (gases); BBr3 (liquid); BI3 (lowmelting point solid) BX3 acts as Lewis acidsBoron halides are highly reactive, volatile compounds. The gas BF3 acts as a Lewis acid with ammonia. Vacant P orbitalGeneral PropertiesThe com

6、pounds which are coordinatively unsaturated (e.g.BCl3) are very strong Lewis acids. Tetrahedral adducts and anions are common, for example: BF3:O(C2H5)2BF4-B(C6H5)4-Boron SubhalidesBX3 are the most common halides.Extensive sub-halide chemistry though, e.g. B4Cl4 and B8F12.B10F12 structurally charact

7、erised.AAAA Metal Borides10B absorbs neutrons strongly. 40 tonnes of boron carbide were dropped on Chernobyl.Boron carbides also used in light-weight protective armour and bullet-proof clothing. Metal borides can be prepared by direct combination of elements:Ca + 6B CaB6Metal-rich borides (e.g. TiB2

8、) can have higher conductivities than parent metals.Also much more inert and harder.B-Rich borides contain B-clustersHydridesboron compounds of hydrogen are called boranes Molecular, volatile compounds; BnHm Simplest borane diborane, B2H6Bonding in DiboraneThe B-H-B unit is held together by 2e.This

9、is called a 3 centre - 2 electron bond (3c2e).The orbital basis can be made up of two sp3 hybrids of the B atoms and two H(1s) orbitals.The remaining boron orbitals form normal 2c2e bonds to the terminal Hs.BBHH3c2e Bonds in DiboraneThe two electrons occupy the fully bonding combination, so that the

10、 overall bond order between the B and the bridging H is 1/2.3c2e Bonds3c2e bonds are occasionally shown in structural diagrams like this:Bond Energies:BH381 kJ/molBHB441 kJ/mol1.19 1.32 Electron DeficiencyAll boranes are electron deficient.The need to form 3c2e bonds (BHB and BBB) causes the molecul

11、es to curl-in on themselves.The more electron deficient the more spherical a molecule es.For example B6H62- is more electron deficient than B4H10Reactions of BoranesBoranes undergo a wide variety of reactions.Oxidation to produce oxidesPyrolysis to produce more complex boranesAttack by nucleophiles

12、and electrophiles.Reduction to borane anions.Reactions with bases.Often the reactions of boranes can be classified in terms of the reaction of terminal or bridging hydrogens.Pyrolysis of DiboraneB2H6B4H10B5H11B5H9B10H14200oC100oCH2/100oC190oC120oC60oCH2/100oCMany complex boranes are known and all co

13、ntain B-H-B bonds.closo B7H72-nido B6H10arachno B5H11闭(笼)式开(巢)式网式cagenestspiders webMechanism of PyrolysisKey step is dissociation of B2H6 into highly reactive BH3:For example, synthesis of B4H10:B2H6 2BH3B2H6 + BH3 B3H7 + H2BH3 + B3H7 B4H10Handling BoranesBoranes are TOXIC and combust EXPLOSIVELY i

14、n air.Lots of shielding, gloves & face protection are necessary.Only use small quantities, so if there is an accident it can be contained. Use vacuum techniques for handling and transferring.General Reactions of DiboraneReaction with oxygen (extremely exothermic)B2H6 + 3O2 B2O3 + H2O H = -2160 kJ/mo

15、leReaction with waterB2H6 + 6H2O 2B(OH)3 + 6H2B2H6 + 6ROH 2B(OR)3 + 6H2Reaction with weak acids2B2H6 + 2HCl 2B2H5Cl + H2Reaction with HClTerminal H are replacedB2H6 + Cl2 2BCl3 + 6HClReaction with Cl2Reactions of Diborane with AminesB2H6 + 2NH3 H2B(NH3)2+BH4-This reaction is the result of the electr

16、on deficient nature of the 3c-2e bridge which are sites for nucleophillic attack. Small amines can give unsymmetrical cleavage of diborane. H2B(NH3)2+ + 2PR3 H2B(PR3)2+ + 2NH3Boronium ion products are tetrahedral and undergo substitution by bases.If large amines are used like (CH3)3N and pyridine a

17、symmetric cleavage of diborane occurs. B2H6 + 2N(CH3)3 2H3B N(CH3)3These products obtained from the symmetrically cleaved diborane are Lewis Acid adducts.Reactions of Boranes with Reducing Agents.2B2H6 + 2Na NaBH4 + NaB3H8B2H6 + NaBH4 NaB3H8 + H2 Reduction of diborane with sodium borohydride also a

18、route to polyhedral anionic borane. Diborane Summary: Unique bonding and versatile chemical reactions.This lead to the a Nobel Prize. carborane 碳硼烷Carboranes or carbaboranes are compounds having as the basic structural unit a number of C and B atoms arranged on the vertices of a triangulated polyhed

19、ron. Their structure are closely related to those of the isoelectronic boranes.metallocarboraneBorazineInorganic Benzene 无机苯Inorganic Benzene 无机苯Unlike benzene, borazine undergoes addition reactions: Notice where the H+ and the Cl- end up: This illustrates how unrealistic the formal charges on the b

20、oron and nitrogen atoms really are! Like benzene, borazine can form plexes with transition metals: Other Boron CompoundsBoron nitride BNBN layer structureComparison with graphiteIsoelectronic with C-C CO(NH2)2 + B(OH)3 BCl3 + NH3 Higher T & P can convertBN to diamond structure,harder than diamond.Bo

21、rax bead reactionsBoron resembles silicon more than aluminum in some ways:B2O3 and B(OH)3 are acidic rather like SiO2 and Si(OH)4 whereas the Al compounds are weakly amphoteric. The borates have some features in common with the silicates. The halide compounds of B and Si are readily hydrolyzed (exce

22、pt BF3) whereas the halide compounds of Al are only partly hydrolyzed. The B and silicon hydrides are volatile molecular compounds, which inflame in air, while AlH3 is an involatile solid. Aluminum, Gallium,Indium and Thallium Aluminum: AlKAl(SO4)212H2OIdentified in 1807 it was not isolated until 18

23、28.WhlerAlCl3 + 3K Al + 3KClum or ium?It is the most abundant metal iin the earths crust.Aluminum as a precious metal?He didnt use silverware.That 9-inch aluminum pyramid, which completes the top of the structure as it narrows to a point, is 100-ounces of solid aluminum, part of the monuments lightn

24、ing protection system. In the 1880s, aluminum was a rare metal, selling for $1.10 per ounce and used primarily for jewelry. The pyramid was the largest piece of aluminum of its day and was such a novelty that it was displayed at Tiffanys jewelry store in New York before it was placed at the top.Hall

25、-Heroult ProcessCryolite Na3AlF62Al2O3 + 3C 4Al(l) + 3CO2(g)He was only 23!GalliumGallium ArsenideM.P. = 29.78oCSemiconductor ApplicationsElectrolysis of GaO and potash.Now a byproduct of Al production.liquid 29.78oC - 2403oCIndium and ThalliumIndium and Thallium were discovered by spectroscopy. In

26、is rare, toxic, and $. Why is it so important?(16) anion vacancies(48) lattice anions(8) b site cations(24) d site cationsCubic Bixbyite Structure of InOoxygeninequivalent In centersvacant oxygen (n-type conductivity)Sn replaces In in a ratio of 5-9% for ITOTransparent electrodeAluminumAluminum is a

27、 silvery white metal. The surface of aluminum metal is covered with a thin layer of oxide that helps protect the metal from attack by air. So, normally, aluminum metal does not react with air. If the oxide layer is damaged, the aluminum metal is exposed to attack. even by water. GalliumSemiconductor

28、 industry: GaAs, GaPDiode laserIndiumSemiconductor industryGlass sealing alloysDental alloysThalliumElectronic components: thallium activated NaI crystal in photomultiplier tubeGlass sealHigh temperature superconductorTl compounds are toxic.Reaction of AlAlizarin-S (or sodium alizarin sulphonate) re

29、agentred precipitate or lake in basic solution, which is fairly stable to diluteacetic acid.Alumina, Al2O3Great hardness ( Mohs scale 9), high mp, chemical inertnessCrystal form containing metal ion impurities:ruby (Cr III, red)sapphire (Fe II/III, Ti IV, blue)oriental emerald (Cr III/V III, green)Compounds of Aluminum- form红宝石(Cr3+) 蓝宝石(Fe3+,Cr3+) 黄玉/黄晶(Fe3+)Alumina fiberVery high strength, high resistance to heat 1400 oC, in diameter of 1/25 of human hair, fl