第十二章氧族元素chapter12oxygenfamily

1、第十二章 氧族元素 Chapter 12 Oxygen Family Elements,Oxygen Sulphur Selenium O S Se Tellurium Polonium Te Po 也稱為成礦元素 (ore-forming element)

2、,§12-1 Oxygen and its compounds 一、Simple substance 1. 除了He、Ne、Ar以外，氧與所有元素化合，只有與氟化合時(shí)，才呈還原性。 2. 最常見的氧化數(shù)為-2,還有+2 (OF2) , +4[O(O2)] , +1(O2F2) , -1(H2O2) 3. 氧的單鍵離解能為142KJ·mol-1，而硫?yàn)?68KJ·mol-1。氧分子離解能

3、為494 kJ/mol,解釋: (1) 氧的原子半徑小，孤對(duì)電子對(duì)之間有較大的排斥作用 (2) 氧原子沒有空的d軌道，不能形成d—p?鍵，所以O(shè)—O單鍵較弱 對(duì)于O2分子而言，除了σ鍵外，還有二個(gè)三電子π鍵，所以O(shè)2—2O比較困難，要求加熱到2000oC ，要求紫外光照射 氧元素在地球上的豐度最高，達(dá)58%(以mol計(jì)),,二、Compounds: 1. [-2]O.S. 最重要的化合物

4、是水。 水分子軌道能級(jí)圖如右圖， 它解釋了水存在四個(gè)第一電離 勢(shì)。 分子軌道表示為：(σS) 2(σZ) 2(σXnon) 2(πYnon)2,The 1s, 2s and 2pz orbitals of oxygen are symmetric (i.e., unchanged) with respect to all three symmetry operations. They are giv

5、en the symmetry classification a1. The 2px orbital, since it possesses a node in the s2 plane (and hence is of different sign on each side of the plane) changes sign when reflected through the s2 plane or when rotated by

6、 180° about the C2 axis. It is classified as a b2 orbital. The 2py orbital is antisymmetric with respect to the rotation operator and to a reflection through the s1 plane. It is labelled b1.    The hydrog

7、en 1s orbitals when considered separately are neither unchanged nor changed in sign by the rotation operator or by a reflection through the s2 plane. Instead both these operations interchange these orbitals. The hydrogen

8、 orbitals are said to be symmetrically equivalent and when considered individually they do not reflect the symmetry properties of the molecule. However, the two linear combinations  (1s1 + 1s2)  and  (1s1

9、- 1s2) do behave in the required manner. The former is symmetric under all three operations and is of a1 symmetry while the latter is antisymmetric with respect to the rotation operator and to a reflection through the p

10、lane s2 and is of b2 symmetry.    The molecular orbitals in the water molecule are classified as a1, b1 or b2 orbitals, as determined by their symmetry properties. This labelling of the orbitals is analogous t

11、o the use of the s-p and g-u classification in linear molecules. In addition to the symmetry properties of the atomic orbitals we must consider their relative energies to determine which orbitals will overlap significant

12、ly and form delocalized molecular orbitals.,The molecular orbitals in the water molecule are classified as a1, b1 or b2 orbitals, as determined by their symmetry properties. This labelling of the orbitals is analogous to

13、 the use of the s-p and g-u classification in linear molecules. In addition to the symmetry properties of the atomic orbitals we must consider their relative energies to determine which orbitals will overlap significantl

14、y and form delocalized molecular orbitals.    The 1s atomic orbital on oxygen possesses a much lower energy than any of the other orbitals of a1 symmetry and should not interact significantly with them. The mo

15、lecular orbital of lowest energy in H2O should therefore correspond to an inner shell 1s atomic-like orbital centred on the oxygen. This is the first orbital of a1 symmetry and it is labelled la1. Reference to the forms

16、of the charge density contours for the la, molecular orbital substantiates the above remarks regarding the properties of this orbital. Notice that the orbital energy of the la1 molecular orbital is very similar to that

17、for the 1s atomic orbital on oxygen. The 1a1 orbital in H2O is, therefore, similar to the ls inner shell molecular orbitals of the diatomic hydrides.    The atomic orbital of next lowest energy in this system

18、is the 2s orbital of a1 symmetry on oxygen. We might anticipate that the extent to which this orbital will overlap with the (1s1 + 1s2) combination of orbitals on the hydrogen atoms to form the 2a1 molecular orbital will

19、 be intermediate between that found for the 2s molecular orbitals in the diatomic hydrides CH and HF. The 2s orbital in CH results from a strong mixing of the 2s orbital on carbon and the hydrogen 1s orbital. In HF the p

20、articipation of the hydrogen orbital in the 2s orbital is greatly reduced, a result of the lower energy of the 2s atomic orbital on fluorine as compared to that of the 2s orbital on carbon.,Aside from the presence of the

21、 second proton, the general form and nodal structure of the 2a1 density distribution in the water molecule is remarkably similar to the 2s distributions in CH and HF, and particularly to the latter. The charge density ac

22、cumulated on the bonded side of the oxygen nucleus in the 2a1 orbital is localized near this nucleus as the corresponding charge increase in the 2s orbital of HF is localized near the fluorine. The charge density of the

23、2a1 molecular orbital accumulated in the region between the three nuclei will exert a force drawing all three nuclei together. The 2a1 orbital is a binding orbital.    Although the three 2p atomic orbitals are

24、 degenerate in the oxygen atom the presence of the two protons results in each 2p orbital experiencing a different potential field in the water molecule. The nonequivalence of the 2p orbitals in the water molecule is evi

25、denced by all three possessing different symmetry properties. The three 2p orbitals will interact to different extents with the protons and their energies will differ.    The 2px  orbital interacts most s

26、trongly with the protons and forms an orbital of b2 symmetry by overlapping with the (1s1 - 1s2) combination of 1s orbitals on the hydrogens. The charge density contours for the lb2 orbital indicate that this simple LCAO

27、 description accounts for the principal  features of this molecular orbital. The lb2 orbital concentrates charge density along each O-H bond axis and draws the nuclei together. The charge density of the 1b2 orbital

28、binds all three nuclei. In terms of the forces exerted on the nuclei the 2a1 and lb2 molecular orbitals are about equally effective in binding the protons in the water molecule.,The 2pz orbital may also overlap with the

29、hydrogen 1s orbitals, the (1s1 + 1s2) a1 combination, and the result is the 3a1 molecular orbital. This orbital is concentrated along the z-axis and charge density is accumulated in both the bonded and nonbonded sides of

30、 the oxygen nucleus. It exerts a binding force on the protons and an antibinding force on the oxygen nucleus, a behaviour similar to that noted before for the 3s orbitals in CH and HF.     The 2py orbital

31、 is not of the correct symmetry to overlap with the hydrogen 1s orbitals. To a first approximation the 1b1 molecular orbital will be simply a 2py atomic orbital on the oxygen, perpendicular to the plane of the molecule.

32、Therefore, the 1b1 orbital does resemble a 2p atomic orbital on oxygen but one which is polarized into the molecule by the field of the protons. The 1b1 molecular orbital of H2O thus resembles a single component of the 1

33、p molecular orbitals of the diatomic hydrides. The 1b1 and the 1p orbitals are essentially nonbinding. They exert a small binding force on the heavy nuclei because of the slight polarization. The force exerted on the pro

34、tons by the pair of electrons in the 1b1 orbital is slightly less than that required to balance the force of repulsion exerted by two of the nuclear charges on the oxygen nucleus. The 1b1 and 1p electrons basically do no

35、 more than partially screen nuclear charge on the heavy nuclei from the protons.,In summary, the electronic configuration of the water molecule as determined by molecular orbital theory is 1a212a211b223a211b21The la1

36、 orbital is a nonbinding inner shell orbital. The pair of electrons in the la1 orbital simply screen two of the nuclear charges on the oxygen from the protons. The 2a1, 1b2 and 3a1 orbitals accumulate charge density in t

37、he region between the nuclei and the charge densities in these orbitals are responsible for binding the protons in the water molecule. Aside from being polarized by the presence of the protons, the lb1 orbital is a non-i

38、nteracting 2py orbital on the oxygen and is essentially nonbinding.,http://www.chemistry.mcmaster.ca/esam/Chapter_8/section_6.html,Contents from http://butane.chem.uiuc.edu/pshapley/312/Lectures/L10/index.html,,,,,,B2A1

39、,2px B12py B2,2px B12py B2,2px B12py B2,http://www.chemistry.mcmaster.ca/esam/Chapter_8/section_6.html#Fig_8-11.,Contour maps of the molecular orbital charge densities for H2O. The maps for the la1, 2a1, 3a1and 1b2 or

40、bitals (all doubly-occupied) are shown in the plane of the nuclei. The lb1 orbital has a node in this plane and hence the contour map for the 1b1 orbital is shown in the plane perpendicular to the molecular plane. The to

41、tal molecular charge density for H2O is also illustrated. The density distributions were calculated from the wave function determined by R. M. Pitzer, S. Aung and S. I. Chan, J. Chem. Phys. 49, 2071 (1968).,2. [ -1 ] O.

42、S. The most important peroxide is that of hydrogen (1) Structure: 是極性分子，即兩個(gè)氫原不在同一個(gè)平面 (2) Properties: 它是一個(gè)極好的離子性溶劑，與水互溶，這是由于能形成新的hydrogen bond , 在實(shí)驗(yàn)室中常用3%—30%的過氧化氫水溶液稱為雙氧水（perhydrol）,b. H2O2是一種弱酸

43、 H2O2 + H2O = H3O+ + HO2- c. 在酸性條件下，H2O2是極好的氧化劑， 在堿性條件下，H2O2是中等的氧化劑。 過氧化氫在水溶液中，不論是氧化劑，還是還原劑，都在反應(yīng)體系中不引入任何雜質(zhì)： 2H+ + H2O2 + 2e 2H2O O2 + 2H+ + 2e H2O2,,,d. 從上面的電位圖來看H2O2不穩(wěn)定 (i

44、) 在OH-介質(zhì)中比H+介質(zhì)中分解快 (ii) 若有重金屬離子Fe2+ , Mn2+ , Cu2+ , Cr2+等都大大加快H2O2的分解 (iii) 波長為320—380nm的光促使H2O2分解 (iv) 受熱加快分解,http://pubs.acs.org/doi/full/10.1021/ja411705d,Bubble-Propelled Micromotors,(3) Preparation: a.

45、BaO2 + H2SO4 = BaSO4↓ + H2O2 BaO2 + CO2 + H2O = BaCO3 + H2O2 b. 電解—水解法 電解：2NH4HSO4 = (NH4)2S2O8 + H2↑ 過二硫酸銨發(fā)生水解: (NH4)2S2O8 + 2H2SO4 = H2S2O8 + 2NH4HSO4 H2S2O8 + H2O = H2SO4 + H2SO5

46、 H2SO5 + H2O = H2SO4 + H2O2,,C. 乙基蒽醌法: H2 + O2 = H2O2 (乙基蒽醌為催化劑) (4) Application: 利用H2O2的氧化性，可漂白毛、絲織物 火箭的氧化劑 用來恢復(fù)古畫的色彩 利用H2O2的還原性，可以除Cl2 3%的H2O2可做殺菌劑,(5) Identification: 在重鉻酸鹽的酸性溶液中

47、，加入少許乙醚和過氧化氫溶液并搖蕩，乙醚層出現(xiàn)藍(lán)色的 [CrO(O2)2·(C2H5)2O] 此法可用來鑒別鉻，同時(shí)可確認(rèn)是CrO42-或Cr2O72- 若不加乙醚，水溶液中的CrO5再與H2O2反應(yīng)，放出O2↑,3. [ I , II , IV ] O.S. O2F2 , OF2 , O(O2) (1) O2F2 dioxydifluoride : 反磁性分子，與H2O2結(jié)構(gòu)類

48、似，紅色揮發(fā)性液體 O2 + F2 = O2F2 不穩(wěn)定 O2F2 + PtF5 = O2+[PtF6-] + 1/2F2 此反應(yīng)中O2F2即是氧化劑又是還原劑,(2) OF2 Oxygen difluoride: 非直線型分子，有毒，淺黃色氣體，是強(qiáng)氧化劑和氟化劑 2F2 + 2NaOH = OF2 + 2NaF + H2O (3) O3 Ozone: 可看作

49、O(O2)，實(shí)際上是O2的同素異形體（allotrope）,a. 它是反磁性物質(zhì)（diamagnetic material） 它有兩個(gè)σ鍵，一個(gè)34Π 。即中心氧原子采取SP2雜化，其中兩個(gè)單電子軌道與另外二個(gè)原子形成兩個(gè)σ鍵，第三個(gè)雜化軌道有一對(duì)孤電子對(duì)，形成σnon 。 b. Physical properties 它是一種非常毒的藍(lán)色氣體，有特殊的腥臭味；少量O3可以凈化空氣、大量O3對(duì)人體有害

50、。,液態(tài)O3是深藍(lán)色，固態(tài)O3是暗紫色，由于O3的極化作用與極化率都大于O2 ，所以其熔沸點(diǎn)比O2高，比O2易溶于水，有顏色。 c. Chemical properties: ?G= -326KJ·mol-1其氧化能力大于O2 ，如： O3 + XeO3 + 2H2O = H4XeO6 +O2↑ PbS + 4O3

51、= PbSO4 + 4O2↑ 2I- + O3 + H2O = I2 + O2 + 2OH- 可以定量測定I-,,d. Preparation: 3O2 = 2O3 條件為放電或hv，所以在高空約25 km處有一臭氧層 e. Applications: 臭氧可氧化CN-而解毒，故常用來治理電鍍工業(yè)中的含氰廢水，不會(huì)引起二次污染 氧化有機(jī)物，可把烯烴氧化并確定雙鍵的位置:CH

52、3CH2CH=CH2 CH3 CH2CHO + HCHOCH3CH=CHCH3 2CH3CHO,,,§12-2 Sulfur and its compounds一、The simple substance 1. 在自然界中存在天然單質(zhì)的硫，主要在火山區(qū)，這是因?yàn)?2H2S + SO2 = 3S↓ + 2H2O 2H2S + O2 = 2S↓ + 2H2O

53、 反應(yīng)物中的H2S來自地下硫化物礦床與高溫水蒸汽的反應(yīng),2. Allotrope : (1) S8：最穩(wěn)定的形式，成環(huán)狀（ring）或皇冠狀（crown） 它有兩種形式： 斜方（正交）硫（orthorhombic）呈黃色； 單斜硫（monoclinic）呈淺黃色。 (2) Allotrope的轉(zhuǎn)化 S2是順磁性的，而S4 , S6 , S8 ……都是反磁性的,3. Chemical pro

54、perties (1) 與非金屬（除稀有氣體、N2、I2）、金屬（除Au、Pt）的反應(yīng)2Al + 3S = Al2S3 Fe + S = FeSHg + S = HgS (研磨) S + O2 = SO2 (2) 在沸騰的堿液中發(fā)生歧化3S + 6NaOH = 2Na2S + Na2SO3 + 3H2O 4. preparation3FeS2 + 12C + 8O2 = Fe3O

55、4 + 12CO + 6S,二、Compounds 1. [ -2 ]O.S. (1) Hydrolysis S2- + H2O = HS- + OH- SiS2 + 3H2O = H2SiO3 + 2H2S Al2S3 + 6H2O = 2Al(OH)3 + 3H2S (2) interaction: Na2S + CS2 = Na2CS3

56、 Na2CS3 + H2SO4 = Na2SO4 + H2CS3 H2CS3 = H2S + CS2,(3) reduction: 其氧化產(chǎn)物為S、SO2、H2SO4，取決于反應(yīng)條件 2KMnO4 + 5H2S + 3H2SO4 = 2MnSO4 + 5S↓ + K2SO4 + 8H2O 2H2S + O2 = 2S↓ + 2H2O H2S + I2 = 2HI + S↓

57、 H2S + 4Br2 = 4H2O + H2SO4 + 8HBr,(4) 許多硫化物有顏色且難溶于水，可用于分離，鑒別陽離子隨著原子序數(shù)增加，顏色加深，這主要是硫化物中共享的離域鍵增加 (5)硫化物可分成導(dǎo)體、半導(dǎo)體和絕緣體e.g. TiS2: Metallic conductivity，ZrS2: Semiconductivity，HfS2: Dielectric,2. [ -2/n ] O.S.

58、 多硫化物 ( polysulfide or persulfide ) (1) Na2S + (n-1)S = Na2Sn 酸化 H2Sn (NH4)2S + (N-1)S = (NH4)2Sn 氫離子 (2) Redox reactions: 3Na2S2 + As2S3 = 2

59、Na3AsS4 + S 4FeS2 + 11O2 = 2Fe2O3 + 8SO2,,,,H2S + (n-1)S,3. [ +4 ] O.S. SHal4（SF4） SOHal2（SOF2、SOCl2） SO2 (1) 與H2O反應(yīng) SO2 + H2O = H2SO3不能從水溶液中分離出來，是相當(dāng)強(qiáng)還原劑 SOCl2 + 2H2O = 2HCl + H2SO3 SF4 +

60、3H2O = 4HF + H2SO3 (2) 既是氧化劑，又是還原劑，能發(fā)生歧化反應(yīng) SO2 +H2S = 3S + 2H2O SO2 + Br2 + 2H2O = H2SO4 + 2HBr 4Na2SO3 = 3Na2SO4 + Na2S （加熱）,4. [ +6 ] O.S.(1) 濃硫酸的特性：吸水性，脫水性，氧化性，鈍化性等。(2) SF6: SF6 + 3H2O = SO3

61、 + 6HF 雖然在水溶液中?G<<0，但SF6非常穩(wěn)定，不與水反應(yīng)，這顯然是動(dòng)力學(xué)因素控制該反應(yīng)。 SF6不與堿酸反應(yīng)，這是由于中心原子的價(jià)(+6)與配位數(shù)(6)飽和所產(chǎn)生的動(dòng)力學(xué)因素，以及高的電離能所致（19.3 ev）, SF6是電介質(zhì)，且分子量大，所以作為高壓發(fā)電機(jī)中的氣相絕緣體。,(3) S(VI)的含氧化合物中的配位數(shù)為4，所以SO3很容易聚合（polymerize），如右圖。 SO3

62、 + HF =H[SO3F] 其中HSO3F的酸性與HClO4一樣強(qiáng)，而SbF5· HSO3F稱為超酸。,“Superacid” and “Superbase”,Olah received the 1994 Nobel Prize in Chemistry for his pioneering research on carbocations and their role in the chemistry of hydr

63、ocarbons. In particular, he developed superacids (a term he coined) that are much stronger than ordinary acids, are non-nucleophilic, and are fluid at low temperatures. In such media (examples include HF-SbF5 and SbF5-SO

64、2ClF-SO2F2) carbocations are stable and their physical properties, such as NMR spectra, can be observed, thus allowing details of their structures to be determined. Besides trivalent ions, of which CH3+ is the parent, Ol

65、ah demonstrated the existence of higher coordinate carbocations such as CH5+. These species do not violate the octet rule, but involve 2-electron 3-center bonding.Olah was born and educated in Hungary, moved to Canada (

66、Dow Chemical) after the 1956 Hungarian uprising, and ultimately to the U.S.A. He was professor and chairman of chemistry at Case Western Reserve University before moving to the University of Southern California, where he

67、 is distinguished professor at USC's Loker Hydrocarbon Research Institute. Olah's many honors besides the Nobel include the ACS awards in Petroleum Chemistry(1964) and for Creative Work in Synthetic Organic Chemi

68、stry (1979), and the Roger Adams Award in Organic Chemistry (1989).,George Andrew OlahHungarian–American chemist (1927–) Olah's "magic acid", so-named for its ability to attack hydrocarbons, is prepared b

69、y mixing antimony pentafluoride (SbF5) and fluorosulfuric acid. The name was coined after one of Professor Olah's post-doctoral associates placed a candle in a sample of magic acid. The candle was dissolved, showing