中国科技大学：《无机化学》第十四章碳族元素 The Carbon Family Elements.doc_大学文库

202 第十四章碳族元素 Chapter 14 The Carbon Family Elements Carbon (C) Silicon (Si) Germanium (Ge) Stannum (Sn) Plumbum (Pb) §14-1 碳及其化合物 Carbon and its Compounds 一、General Properties 1．根据 σ 键的数目，碳可采取 sp、sp2、sp3 杂化，其最大配位数为 4 2．由于碳—碳单键的键能特别大，所以 C－C 键非常稳定,具有形成均键(homochains)的倾向 C－C N－N O－O F－F E (kJ·mol−1 ) 374 250 210 159 实例 H3C－CH3 H2N－NH2 HO－OH 从碳到氮的单键键能的突减，是由于 N2 分子中氮原子之间非键电子对排斥的缘故。二、The Simple Substance 1．在第二周期中，氟、氧和氮都以双原子分子存在：F2、O2 和 N2；而碳存在多聚物，其理由为：O2 和 N2 的多重键要比 σ 单键（均键）强得多如： , E (kJ·mol−1 ) 494 ＞ 210 + 210 , 946 ＞ 250 + 250 而： E (kJ·mol−1 ) 627 ＜ 374 + 374 即 C2 分子中的多重键比均链中的两个 σ 单键之和小，所以碳往往形成多原子均键，虽然在星际空间存在有 C2(g)分子。 2．Allotropes: diamond、graphite、fullerene (C60、C70)、carbin (carbon fibers) (1) 熵 Scarbin＞Sgraphite＞Sdiamond (2) dC-C (nm): diamond ＞ graphite ＞ benzene ＞ ethylene ＞ carbin ＞ acethylene (3) Cgraphite → Cdiamond r Hm ＞0，r Sm ＜0 根据平衡，需要高压 6 10 1.0 10 Pa 9 10  −  ，(because of the insignificant reduction of volume)，升高温度不利于平衡的移动，但为了达到该过程可以接受的速率，反应温度大约在 2000℃，近来已发明一种低压生产金刚石的方法：把金刚石晶种（seed）放在气态碳氢化合物（甲烷 methane，ethane）中，温度升高到 1000℃，可以得到金刚石粉末或者 crystal whiskers (4) C60 由 12 个正五边形和 20 个正六边形组成，每个碳原子以 sp3、sp2 杂化轨道与相邻的三个碳原子相连，使∠CCC 小于 120而大于 10928，形成曲面，剩余的 p 轨道在 C60 球壳的外围和内腔形成球面π键，从而具有芳香性。 O O N N N N N C C C C C O O O

203 欧拉方程：面数(F) + 顶点数(V) = 棱数(E) + 2 a．structure：根据欧拉定理，通过 12 个正五边形和数个正六边形的连接可以形成封闭的多面体结构：C60 为第一个五边形间互不相邻的封闭笼状结构，C70 为第二个五边形间互不相邻的封闭笼状结构，两个五边形相邻的最小碳笼为 C50，三个五边形相邻的最小碳笼为 C28，不存在六边形的最小碳笼为 C20。 b．properties：科学家认为 C60 将是 21 世纪的重要材料 (i) C60 分子具有球形的芳香性，可以合成 C60Fn，作为超级润滑剂。 (ii) C60 笼内可以填入金属原子而形成超原子分子，作为新型催化剂或催化剂载体，具有超导性，掺 K 的 C60，Tc = 18K，Rb3C60 Tc = 29K，它们是三维超导体。 (iii) C60 晶体有金属光泽，其微晶体粉末呈黄色，易溶于苯，其苯溶液呈紫红色。C60 分子特别稳定，进行化学反应时，C60 始终是一个整体。三、The Compounds 1．[ − 4 ]O.S. covalent CH4, ionic-covalent Al4C3, metallic MC、M2C、M3C 水解性（或与水反应）： Al4C3 + 12H2O 4Al(OH)3 + 3CH4↑ CaC2 + 2H2O Ca(OH)2 + C2H2↑ 20% HfC 和 80%TaC 合金是已知物质中熔点最高的（m.p. = 4400℃） 2．[ + 4 ]O.S. (1) CHal4 a．preparation：CS2 + 2Cl2 CCl4 + S2Cl2 b．properties： hydrolysis CHal4 + 2H2O(g) CO2(g) + 4HHal(g) 从热力学上看是可行的： CF4（r Gm = −150kJ·mol−1），CCl4（r Gm = −250kJ·mol−1）它们之所以不能水解是由于在通常条件下缺乏动力学因素，碳的配位数已饱和，不能与水分子结合。从 CF4→CI4 随着键长的增大,键的强度减弱，稳定性减弱，活泼性增强 (2) COHal2（卤氧化碳，也称为碳酰卤 carbonyl halides）：所有的 COHal2 比 CHal4 的化学性质活泼，特别是它们易水解： COCl2 + H2O CO2 + 2HCl 它们都有极性，都是平面三角形。 COCl2 (光气 phosgene) 是剧毒的光气的制备：CO + Cl2 COCl2 (3) CS2（carbon disulfide） a．preparation (i) C + 2S 900℃ CS2 (ii) 4S(g) + CH4(g) 600℃ Al2O3或硅胶 CS2 + 2H2S b．properties CS2 是易挥发、易燃的无色的有机溶剂明显水解：CS2 + 2H2O CO2 + 2H2S 与碱性硫化物反应：Na2S + CS2 Na2CS3

205 §14-2 硅及其化合物 Silicon and its Compounds 一、General Properties 1．由于 Si 的原子半径大、电离能低、电子亲合能和极化率高，因此 Si 在化学性质上与碳有许多不同之处。例如 Si 和 Si 之间基本上不形成 pπ－pπ键，换言之，Si 的 sp 或 sp2 杂化不稳定。 2．由于 Si 原子的价轨道存在 3d 空轨道，所以 Si 原子的最大配位数可以达到 6，可以形成 d－pπ键，例如 N(SiH3)3 中 N 原子采取 sp2 杂化，分子为平面三角形。这是由于 N 原子上的孤对电子对占有 Si 原子的 3d 空轨道，形成 d－pπ键所致。显然 N(CH3)3 与 N(SiH3)3 的碱性也不同，前者的 Lewis 碱性大于后者。 3．Si 在自然界中占第二位，仅次于氧。About half the earth’s crust consists of silica (SiO2) and silicate, aluminosilicate rocks. 二、The Simple Substance 1．Properties (1) 在通常情况下，硅非常惰性，但加热时与许多非金属单质化合，还能与某些金属反应     ⎯⎯⎯⎯ ⎯→ ⎯⎯⎯⎯ ⎯→     ⎯⎯⎯⎯⎯ ⎯⎯ ⎯⎯     2 600 C O 4 400 C Cl 1000 C N 3 4 2000 C C SiO SiCl Si Si N SiC 3 2 2 2Mg + Si Mg2Si (2) 硅遇到氧化性的酸发生钝化性(passivation),它可溶于 HF－HNO3 的混合酸中 3Si + 4HNO3 + 18HF 3H2SiF6 + 4NO + 8H2O 硅与氢氟酸反应：Si + 4HF SiF4 + 2H2，SiF4 + 2HF H2SiF6 (3) 硅溶于碱并放出 H2：Si + 2KOH + H2O K2SiO3 + 2H2↑ (4) 硅在高温下与水蒸气反应：Si + 2H2O(g) H2SiO3 + 2H2 2．Preparation: (1) SiCl4 + 2Zn Si + 2ZnCl2 (2)SiO2 和 C 混合，在电炉中加热：SiO2(s) + 2C(s) 电炉 Si(s) + 2CO(g)↑ (3) SiO2 + CaC2 Si + Ca + 2CO (4) 硅烷的分解：SiH4 Si + 2H2 用作半导体用的超纯硅（super pure silicon），需用区域熔融（zone melting）的方法提纯。三、The Compounds 1．[ − 4 ] O.S. 硅化物（silicides） (1) IA、IIA 族硅化物：Ca2Si、CaSi、CaSi2 不稳定，与水反应 (2) 副族元素硅化物：Mo3Si、Mo5Si3、MoSi、MoSi2（2050℃）高熔、沸点，不溶于 HF 和王水，仅溶于 HF－HNO3 混合液或者在碱液中 WSi2（2165℃），Ti5Si3（2120℃），V5Si3（2150℃），f 元素的硅化物在反应堆中吸收中子。 2．[ +4 ]O.S. SiHal4，SiO2，Si3N4，SiC 和 SiH4 (1) structure：正四面体结构单元：SiO4、SiS4、SiN4、SiC4

The Discovery of Buckminsterfullerene Discoveries in science are almost always convoluted affairs, not the sud den"Eureka! "of fiction. W. E. Addison had predicted in 1964 that other allotropes of carbon might exist; and David Jones in 1966 actu- ally proposed the existence of"hollow graphite spheroids It was not chemists, however, but two astrophysicists, Donald Huffman of the University of Arizona at Tucson and Wolfgang Kratschmer of the Max Planck Institute for Nuclear Physics at Heidelberg, Germany, who are credited with the first synthesis of fullerenes in 1982. They were interested in the forms of carbon that uld exist in interstellar space. They heated graphite rods in a low ressure atmosphere and obtained a soot. It appeared to have an un sual spectrum, but they attributed that to contamination by oil vapor from the equipment. As a result, they lost interest in the experiment Two vears later, an Australian medical researcher, Bill Burch, at the Australian National University produced a sublimable form of carbon hat he patented as"Technogas "This, too, was probably buckminster Harold Kroto of the University of Sussex, England, and Richard Smalley of Rice University, Texas, performed the crucial experiment They were also interested in the nature of carbon in space. When Kroto visited Smalley, the former proposed that they use Smalleys high- powered laser to blast fragments off a graphite surface and then identify he products. Between 4 September and 6 September 1985, they found one batch of products that had a very high proportion of a molecule con taining 60 carbon atoms. Over the weekend, two research students, Jim Heath and Sean O'Brien, altered the conditions of the experiment until time after time, they could consistently obtain this unexpected product How could the formula Co be explained: Kroto recalled the geo desic dome that housed the U.S. pavilion at Expo 67 in Montreal However, he thought the structure consisted of hexagonal shapes, like those making up graphite. The chemists were unaware of the work by the cighteenth-century mathematician Leonhard Euler, who had shown that it was impossible to construct closed figures out of hexagons alone Smalley and Kroto now disagree vehemently over which one of them first realized that a spherical structure could be constructed using 20 hexagons and 12 pentagons. Nevertheless, on 10 September, this was the structure that the group postulated for the mysterious molecule As a result of the disagreement, relations between the two research are acrimonIous The Kroto- Smalley method produced quantities of buckminster fullerene that were too small for chemical studies. The discovery cycle was completed in 1988 when Huffman realized that the method that he and Kratschmer had used several years earlier must have been forming large quantities of these molecules. These two physicists resumed their production of the soot and developed methods for producing consis- tently high yields of the allotropes. From subsequent studies, the chem ical evidence proving the structures of Co and Cm was independently and almost simultaneously produced by the Kroto and the Smalley fullerene research, over 5000 research papers were written about tl of The story of the fullerenes is still developing. In the first decade properties of these allotropes and their many compounds 210

中国科技大学：《无机化学》第十四章 碳族元素 The Carbon Family Elements

中国科技大学：《无机化学》第十四章碳族元素 The Carbon Family Elements