第十二章 氧族元素 Chapter 12 Oxygen Family Elements

1. 第十二章 氧族元素Chapter 12 Oxygen Family Elements

2. Oxygen Sulphur Selenium • O S Se • Tellurium Polonium • Te Po • 也称为成矿元素 • (ore-forming element)

3. §12-1 Oxygen and its compounds • 一、Simple substance • 1. 除了He、Ne、Ar以外，氧与所有元素化 • 合，只有与氟化合时，才呈还原性。 • 2. 最常见的氧化数为-2,还有+2 (OF2) , • +4[O(O2)] , +1(O2F2) , -1(H2O2) • 3. 氧的单键离解能为142KJ·mol-1，而硫 • 为268KJ·mol-1。氧分子离解能为494 kJ/mol

5. 解释: • (1) 氧的原子半径小，孤对电子对之间有较大 • 的排斥作用 • (2) 氧原子没有空的d轨道，不能形成d—p键，所以O—O单键较弱 • 对于O2分子而言，除了σ键外，还有二个三 • 电子π键，所以O2—2O比较困难，要求加热到 • 2000oC，要求紫外光照射 • 氧元素在地球上的丰度最高，达58%(以mol计)

6. 二、Compounds: • 1. [-2]O.S. • 最重要的化合物是水。 • 水分子轨道能级图如右图， • 它解释了水存在四个第一电离 • 势。 • 分子轨道表示为： • (σS)2(σZ)2(σXnon)2(πYnon)2

8. The 1s, 2s and 2pz orbitals of oxygen are symmetric (i.e., unchanged) with respect to all three symmetry operations. They are given 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 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 hydrogen 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 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 - 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 plane 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 to 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 significantly and form delocalized molecular orbitals.

9. 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 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 significantly 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 molecular 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 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 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 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 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 participation 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.

10.    Aside from the presence of the 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 accumulated 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 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 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 evidenced 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 2pxorbital interacts most strongly 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 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 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.

11. The 2pz orbital may also overlap with the 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 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 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. 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 1p 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 protons 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 more than partially screen nuclear charge on the heavy nuclei from the protons.

12. In summary, the electronic configuration of the water molecule as determined by molecular orbital theory is 1a212a211b223a211b21 The la1 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 the 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-interacting 2pyorbital on the oxygen and is essentially nonbinding. http://www.chemistry.mcmaster.ca/esam/Chapter_8/section_6.html

13. Contents from http://butane.chem.uiuc.edu/pshapley/312/Lectures/L10/index.html

15. B2 A1

16. 2px B1 2py B2

17. 2px B1 2py B2

18. 2px B1 2py B2

20. Contour maps of the molecular orbital charge densities for H2O. The maps for the la1, 2a1, 3a1and 1b2 orbitals (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 total 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). http://www.chemistry.mcmaster.ca/esam/Chapter_8/section_6.html#Fig_8-11.

21. 2. [ -1 ] O.S. • The most important peroxide is that of • hydrogen • (1) Structure: • 是极性分子，即两个氢原不在同一个平面 • (2) Properties: • 它是一个极好的离子性溶剂，与水互溶，这是由 • 于能形成新的hydrogen bond , 在实验室中常用 • 3%—30%的过氧化氢水溶液称为双氧水（perhydrol）

22. b. H2O2是一种弱酸 • H2O2 + H2O = H3O+ + HO2- • c. 在酸性条件下，H2O2是极好的氧化剂， • 在碱性条件下，H2O2是中等的氧化剂。 • 过氧化氢在水溶液中，不论是氧化剂，还是 • 还原剂，都在反应体系中不引入任何杂质： • 2H+ + H2O2 + 2e 2H2O • O2 + 2H+ + 2e H2O2

23. d. 从上面的电位图来看H2O2不稳定 • (i) 在OH-介质中比H+介质中分解快 • (ii) 若有重金属离子Fe2+ , Mn2+ , Cu2+ , • Cr2+等都大大加快H2O2的分解 • (iii) 波长为320—380nm的光促使H2O2 • 分解 • (iv) 受热加快分解

24. Bubble-Propelled Micromotors http://pubs.acs.org/doi/full/10.1021/ja411705d

25. (3) Preparation: • a. BaO2 + H2SO4 = BaSO4↓ + H2O2 • BaO2 + CO2 + H2O = BaCO3 + H2O2 • b. 电解—水解法 • 电解：2NH4HSO4 = (NH4)2S2O8 + H2↑ • 过二硫酸铵发生水解: • (NH4)2S2O8 + 2H2SO4 = H2S2O8 + 2NH4HSO4 • H2S2O8 + H2O = H2SO4 + H2SO5 • H2SO5 + H2O = H2SO4 + H2O2

26. C. 乙基蒽醌法: • H2 + O2 = H2O2 (乙基蒽醌为催化剂) • (4) Application: • 利用H2O2的氧化性，可漂白毛、丝织物 • 火箭的氧化剂 • 用来恢复古画的色彩 • 利用H2O2的还原性，可以除Cl2 • 3%的H2O2可做杀菌剂

28. (5) Identification: • 在重铬酸盐的酸性溶液中，加入少许乙醚和过氧化氢溶液并摇荡，乙醚层出现蓝色的 • [CrO(O2)2·(C2H5)2O] • 此法可用来鉴别铬，同时可确认是CrO42-或Cr2O72- • 若不加乙醚，水溶液中的CrO5再与H2O2反应，放出O2↑

29. 3. [ I , II , IV ] O.S. • O2F2 , OF2 , O(O2) • (1) O2F2 dioxydifluoride : • 反磁性分子，与H2O2结构类似，红色挥发 • 性液体 • O2 + F2 = O2F2 不稳定 • O2F2 + PtF5 = O2+[PtF6-] + 1/2F2 • 此反应中O2F2即是氧化剂又是还原剂

30. (2) OF2 Oxygen difluoride: • 非直线型分子，有毒，浅黄色气体，是强氧 • 化剂和氟化剂 • 2F2 + 2NaOH = OF2 + 2NaF + H2O • (3) O3 Ozone: • 可看作O(O2)，实际上是O2的同素异形体 • （allotrope）

31. a. 它是反磁性物质（diamagnetic material） • 它有两个σ键，一个34Π。即中心氧原子采 • 取SP2杂化，其中两个单电子轨道与另外二个原 • 子形成两个σ键，第三个杂化轨道有一对孤电子对，形成σnon 。 • b. Physical properties • 它是一种非常毒的蓝色气体，有特殊的腥臭 • 味；少量O3可以净化空气、大量O3对人体有害。

32. 液态O3是深蓝色，固态O3是暗紫色，由于 • O3的极化作用与极化率都大于O2 ，所以其熔 • 沸点比O2高，比O2易溶于水，有颜色。 • c. Chemical properties: • ∆G= -326KJ·mol-1 • 其氧化能力大于O2 ，如： • O3 + XeO3 + 2H2O = H4XeO6 +O2↑ • PbS + 4O3 = PbSO4 + 4O2↑ • 2I- + O3 + H2O = I2 + O2 + 2OH- 可以定量测定I-

33. d. Preparation: • 3O2 = 2O3 条件为放电或hv，所以在高空约25 • km处有一臭氧层 • e. Applications: • 臭氧可氧化CN-而解毒，故常用来治理电镀工业中 • 的含氰废水，不会引起二次污染 • 氧化有机物，可把烯烃氧化并确定双键的位置: • CH3CH2CH=CH2 CH3 CH2CHO + HCHO • CH3CH=CHCH3 2CH3CHO

34. §12-2 Sulfur and its compounds • 一、The simple substance • 1. 在自然界中存在天然单质的硫，主要在火 • 山区，这是因为 • 2H2S + SO2 = 3S↓ + 2H2O • 2H2S + O2 = 2S↓ + 2H2O • 反应物中的H2S来自地下硫化物矿床与高温 • 水蒸汽的反应

35. 2. Allotrope : • (1) S8：最稳定的形式，成环状（ring）或 • 皇冠状（crown） • 它有两种形式： • 斜方（正交）硫（orthorhombic）呈黄色； • 单斜硫（monoclinic）呈浅黄色。 • (2) Allotrope的转化 • S2是顺磁性的，而S4 , S6 , S8 ……都是反磁性的

37. 3. Chemical properties • (1) 与非金属（除稀有气体、N2、I2）、金属（除Au、Pt）的反应 • 2Al + 3S = Al2S3 Fe + S = FeS • Hg + S = HgS (研磨) S + O2 = SO2 • (2) 在沸腾的碱液中发生歧化 • 3S + 6NaOH = 2Na2S + Na2SO3 + 3H2O • 4. preparation • 3FeS2 + 12C + 8O2 = Fe3O4 + 12CO + 6S

38. 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 • Na2CS3 + H2SO4 = Na2SO4 + H2CS3 • H2CS3 = H2S + CS2

39. (3) reduction: • 其氧化产物为S、SO2、H2SO4，取决于反 • 应条件 • 2KMnO4 + 5H2S + 3H2SO4 = • 2MnSO4 + 5S↓ + K2SO4 + 8H2O • 2H2S + O2 = 2S↓ + 2H2O • H2S + I2 = 2HI + S↓ • H2S + 4Br2 = 4H2O + H2SO4 + 8HBr

40. (4) 许多硫化物有颜色且难溶于水，可用于 • 分离，鉴别阳离子 • 随着原子序数增加，颜色加深，这主要是硫化物中共享的离域键增加 • (5)硫化物可分成导体、半导体和绝缘体 • e.g. TiS2: Metallic conductivity， • ZrS2: Semiconductivity， • HfS2: Dielectric

41. H2S + (n-1)S • 2. [ -2/n ] O.S. 多硫化物 • ( polysulfide or persulfide ) • (1) Na2S + (n-1)S = Na2Sn 酸化 • H2Sn • (NH4)2S + (N-1)S = (NH4)2Sn氢离子 • (2) Redox reactions: • 3Na2S2 + As2S3 = 2Na3AsS4 + S • 4FeS2 + 11O2 = 2Fe2O3 + 8SO2

42. 3. [ +4 ] O.S. • SHal4（SF4） SOHal2（SOF2、SOCl2） SO2 • (1) 与H2O反应 • SO2 + H2O = H2SO3 • 不能从水溶液中分离出来，是相当强还原剂 • SOCl2 + 2H2O = 2HCl + H2SO3 • SF4 + 3H2O = 4HF + H2SO3 • (2) 既是氧化剂，又是还原剂，能发生歧化反应 • SO2 +H2S = 3S + 2H2O • SO2 + Br2 + 2H2O = H2SO4 + 2HBr • 4Na2SO3 = 3Na2SO4 + Na2S （加热）

43. 4. [ +6 ] O.S. • (1) 浓硫酸的特性：吸水性，脱水性，氧化性，钝化性等。 • (2) SF6: SF6 + 3H2O = SO3 + 6HF • 虽然在水溶液中∆G<<0，但SF6非常稳定，不与水反 • 应，这显然是动力学因素控制该反应。 • SF6不与碱酸反应，这是由于中心原子的价(+6)与配 • 位数(6)饱和所产生的动力学因素，以及高的电离能所致 • （19.3 ev）, SF6是电介质，且分子量大，所以作为高 • 压发电机中的气相绝缘体。

44. (3) S(VI)的含氧化合物中的配位数为4，所以SO3很容易聚合（polymerize），如右图。 • SO3 + HF =H[SO3F] • 其中HSO3F的酸性与HClO4 • 一样强，而SbF5· HSO3F称 • 为超酸。

45. “Superacid” and “Superbase” Olah received the 1994 Nobel Prize in Chemistry for his pioneering research on carbocations and their role in the chemistry of hydrocarbons. 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-SO2ClF-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, Olah 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 (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 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 Chemistry (1979), and the Roger Adams Award in Organic Chemistry (1989). George Andrew Olah Hungarian–American chemist (1927–) Olah's "magic acid", so-named for its ability to attack hydrocarbons, is prepared by 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 the ability of the acid to protonate hydrocarbons (which are not basic).

46. A superacid is an acid with an acidity greater than that of 100% sulfuric acid, which has a Hammett acidity function of -12. Commercially available superacids include trifluoromethanesulfonic acid (CF3SO3H), also known as triflic acid, and fluorosulfuric acid (FSO3H), both of which are about a thousand times stronger (i.e. have more negative H0 values) than sulfuric acid. The strongest superacids are prepared by the combination of two components, a strong Lewis acid and a strong Brønsted acid. The strongest super acid system, the so-called fluoroantimonic acid, is a combination of hydrogen fluoride and SbF5. In this system, HF releases its proton (H+) concomitant with the binding of F− by the antimony pentafluoride. The resulting anion (SbF6−) is both a weak nucleophile and a weak base. The proton effectively becomes "naked", which accounts for the system's extreme acidity. Fluoroantimonic acid is 2×1019 times stronger than 100% sulfuric acid, and can produce solutions with a pH down to –25. “Superacid” and “Superbase”

47. In chemistry, a superbase is an extremely strong base. There is no commonly accepted definition for what qualifies as a superbase, but most chemists would accept sodium hydroxide as a 'benchmark' base just as sulfuric acid is a 'benchmark' acid (see superacid). The hydroxide ion is a good benchmark because it is the strongest base that can exist in a water solution; stronger bases neutralize water as an acid by deprotonation, to produce hydroxide (and protonated superbase). Another use that can define superbase is stoichiometric α-deprotonation of a carbonyl compound into an enolate, something that cannot be done by "regular bases". Despite this, the term still doesn't have a standard chemical definition, so for example Proton Sponge may be called "superbase". Organometallic compounds of reactive metals are usually superbases, for example organolithium and organomagnesiums (Grignard reagents). Another type of organic superbase has a reactive metal exchanged for a hydrogen on a heteroatom, such as oxygen (unstabilized alkoxides) or nitrogen (lithium diisopropylamide). “Superacid” and “Superbase”

48. Reactions involving superbases are usually water-sensitive, conducted under an inert atmosphere and at a low temperature. A desirable property in many cases is low nucleophilic reactivity, i.e. a non-nucleophilic base. Unhindered alkyllithiums, for example, cannot be used with electrophiles such as carbonyl groups, because they attack the electrophiles as nucleophiles. In organic synthesis, the Schlosser base (or Lochmann-Schlosser base), i.e. the combination of n-butyllithium and potassium tert-butoxide, is a commonly used superbase. Butyllithium exists as four-, or six-membered clusters, which are kinetically slow to react. The tertiary alcoholate (butoxide) serves to complex the lithium ion, which breaks the butyllithium clusters. This makes the butyllithium kinetically more reactive. Inorganic superbases are typically salts with highly charged, small negative ions, e.g. lithium nitride, which has extreme negative charge density and so is highly attracted to acids, like the aqueous hydronium ion. Alkali and earth alkali metal hydrides (sodium hydride, calcium hydride) are superbases. “Superacid” and “Superbase”

49. (4) 硫代硫酸盐（thiosulphates） • a. 沸腾温度下，亚硫酸钠溶液与S粉混和 • SO32- + S = S2O32- 或者 • 2Na2S + Na2CO3 + 4SO2 = 3Na2S2O3 + CO2（价态变化） • b. 这两种硫是不等价的 • c. 不稳定，在酸性条件下分解，只有PH >4.6时才 • 不分解 • d. 是一种还原剂，也是一种络合剂 • 2Na2S2O3 + I2 = Na2S4O6 + 2NaI • AgBr + 2Na2S2O3 = Na3[Ag(S2O3)2] + NaBr

50. (5) 连硫酸及其盐 • a. 通式：H2SxO6 ( X=2—6 ) • b. 连硫酸不稳定，易分解 • H2S2O6 = H2SO4 + SO2 • H2S4O6 = H2SO4 + SO2 + 2S • c. 制备 • 2MnO2 + 3H2SO3 = MnSO4 + MnS2O6 + 3H2O • BaS2O6 + H2SO4 = BaSO4↓ + H2S2O6