第九章稀有氣體參考資料

1、第九章稀有氣體Chapter 9 The Rare Gases153從1894-1900年期間上面稀有氣體相繼全部被發(fā)現(xiàn)，其中Helium (He)太陽Krypton (Kr)穩(wěn)定的Electronic configuration :Neon (Ne)新的Xenon (Xe)陌生的 ns2np6except He 1s2Argon (Ar)懶惰的Radon (Rn)發(fā)光的Ramsay功績最大，他榮獲1904年Nobel化學(xué)獎。1892年，J.W.S.Rayleigh發(fā)現(xiàn)從空氣中分離出來的氮?dú)饷芏缺葟幕?合物中分離出來的氮?dú)饷芏嚷灾?1.2565/1.2507),但不知其原因。W.Ramsay緊

2、隨其后,以敏銳的觀察力和高超的實(shí)驗(yàn)技術(shù)，與合作者經(jīng)過幾年的艱苦努力，終于發(fā)現(xiàn)和離析了幾 乎一整族稀有氣體。一、General Properties:1 .它們都是單原子分子(monatomic molecular),在通常條件下，它們都是氣體，也稱為 惰性氣體(noble or inert gases)。2 .蒸發(fā)熱、在水中的溶解度以及熔、沸點(diǎn)都很小，并且隨著原子序數(shù)的增加而逐漸升高。 氨是所有氣體中最難液化的物質(zhì)。He的沸點(diǎn)為4.2K, ”的沸點(diǎn)為20.4K。氨冷卻至2.178K,則變成第二種液體(helium II),發(fā)生無粘度流動，稱為超流體 (superfluidity)。 He-II

3、的熱傳導(dǎo)是He-I的106倍，比熱傳導(dǎo)最優(yōu)的金屬銀強(qiáng)得多。3 .由于稀有氣體的最外電子層都有相對飽和的結(jié)構(gòu)( octet rule),這種電子結(jié)構(gòu)是相當(dāng) 穩(wěn)定的，其電子親合勢都接近于零，而且都有很高的電離勢，因此它們在化學(xué)性質(zhì)上 表現(xiàn)為惰性。4 .在自然界中的分布：在接近地球表面的空氣中，每 1000升空氣中約含9.3升僦、18 毫升速、5毫升氮、1毫升氟和0.8升氤，所以液態(tài)空氣是提取稀有氣體的主要原料。5 .用途：氟、氤的同位素在醫(yī)學(xué)上被用來測量腦血流量和研究肺功能，計(jì)算胰島素分泌量。二、Chemical Properties在稀有氣體發(fā)現(xiàn)后一段時間內(nèi)(1900-1960年)，把它們作為化

4、學(xué)性質(zhì)上絕對惰性的。直到1962年，Bartlett將PtF6的蒸氣與等摩爾的氤混合，在室溫下制得了XePtF6的橙黃色固體，推翻了持續(xù)了近70年之久的關(guān)于稀有氣體完全化學(xué)惰性的傳統(tǒng)說法。下面我們主要討論氤的氟化物和含氧化合物。1.氤的氟化物(Fluorides of xenon) XeF2、XeF4、XeF6(1) preparation400 C,1atmXe(g) F2(g)XeF2 (s)(由Xe在缺F2情況下加壓反應(yīng))600 C,6atmXe(g) 2F2(g) > XeF4 (s)較易制得，在如上條件下加入Xe和F2 (1:5)混合物，幾十小時后便制得。-300 C,60at

5、m,、Xe(g) +3F2(g)-XeF6(s)(Xe : F2 = 1:20)或 XeF4(s)+F?(g)/ XeFe(s)(在常壓下)Irradiating a xenon-fluorine mixture with ultra-violet light at ordinary temperature produces XeF2 (together with some XeF 4)為什么Xe與F2混合如此容易化合但六十多年間卻沒有能合成出Xe的化合物?主要有這幾方面原因：當(dāng)時擁有的Xe的量太少；絕對干燥的玻璃儀器不能獲得；實(shí)驗(yàn)技術(shù)落后，更重要的是思想上有框框。(2) properties

6、a.氤的氟化物都與水發(fā)生反應(yīng)：(i) XeF 2在水中的溶解放出刺激性臭味，在酸性溶液中水解很慢，但在堿性溶 液中水解很快：2XeF2(s) + 2H 2O。)2Xe(g) + 4HF(l) + O 2(g)XeF2在堿性溶液中發(fā)生 Redox反應(yīng)：1 XeF2(s) 2OH "(aq)Xe(g) - O2(g) 2F"(aq) H2O(l)2(ii) XeF 4在水中既發(fā)生歧化反應(yīng)，又發(fā)生氧化還原反應(yīng)：6XeF4(s) + 12H 2O。) 2XeO 3(s) + 4Xe(g) + 3O 2(g) + 24HF(l)分解成：3XeF4(g) + 6H 2O(l) 3Xe(

7、g) + 3O 2(g) + 12HF(l)(與水的氧化還原反應(yīng))3XeF 4(s) + 6H 2O(l)2XeO 3(s) + Xe(g) + 12HF(l)(歧化反應(yīng))所以上述反應(yīng)方程式只是 XeF4等摩爾參與歧化反應(yīng)以及與水的氧化還原 反應(yīng)的配平結(jié)果。實(shí)際上這是一個多重配平的方程式。(iii) XeF 6(s) + H2O。)XeOF4(l) + 2HF(l) XeOF 4(l) + 2H 2O(l)XeO3(s) + 4HF(l)b.氤的氟化物都是強(qiáng)氧化劑XeF2(s) + CH 2= CH2(g)CH2F CH2F(s) + Xe(g)XeF4(s) + 2SF«g)2SF

8、6(g) + Xe(g)XeF 6(g) + 8NH 3(g)Xe(g) + N 2(g) + 6NH 4F(s)可以使 HCl 一 Cl2, Ce(III) 一 Ce(IV), NH3 一 N2 XeF 6化學(xué)性質(zhì)非?；顫?，甚至與石英反應(yīng)：2XeF6(g) + SiO 2(s)2XeOF 4。)+ SiF 4(g)XeF6在堿性條件下也能發(fā)生歧化反應(yīng)：4XeF6 + 18Ba(OH) 23Ba2XeO6 + Xe + 12BaF 2 + 18H 2Oc.氤的氟化物都是良好的氟化劑RbF(s) + XeF 6(s)RbXeF7(s)XeF2(s) + SbF5(l)XeFSbF 6(s)2Xe

9、F2(s) + SbF5(l) Xe 2F3 SbF6- (s)2.氤的氧化物(Oxides of xenon)(1) preparation:a. XeO3由XeF4和XeF6水解制得。b. XeO4由XeF6在Ba(OH) 2中歧化制得的高氤酸鋼BaNeOe,高氤酸鋼再與硫酸反應(yīng)制得：Ba2XeO6(s) + 2H 2SO4(aq) = 2BaSO4(s) + XeO4(g) + 2H 2O(l)(2) properties :a.穩(wěn)定性(stabilization )無色無味XeO3(s)中含有XeO3分子。XeO3在水中穩(wěn)定，(1在固態(tài)時 XeO3會 發(fā)生爆炸(雖然該反應(yīng)經(jīng)常在動力學(xué)上

10、很慢)。它在 OH介質(zhì)中形成HXeO4"離 子：此離子發(fā)生緩慢歧化，得到 XeO4":一 _ - 一 一 - 3XeO 3(s) + OH (aq) HXeO 4K = 1.5 俅8OH -+4HXeOf= Xe +3XeO4+6H2O或者：2HXeO 4Xaq)+ 2OH(aq) XeO6.aq)+Xe(g) +O2(g) +2H2O(l)因此可以得出這樣的結(jié)論：對于氤的含氧化物，在酸性和中性溶液中Xe (VI)穩(wěn)定；在堿性溶液中 Xe MII)穩(wěn)定。XeO6是一種氣體，正四面體幾何構(gòu)型。XeO6緩慢分解成XeO3和。2,當(dāng)XeO,固態(tài)時，即使在室溫下仍然會發(fā)生爆炸。b.

11、氧化性(oxidation ):高氤酸鹽是最強(qiáng)的氧化劑之一。它能把Mn2+分別氧化成MnO l、CIO、CIO 14 一2+5XeO6 + 2Mn + 9H 5HXeO 4 2MnO4 + 2H2Oc.在堿性溶液中，高氤酸鹽的主要形式是HXeO6它被水緩慢還原，然而在酸性溶液中, Reduction is almost instantaneous:21 一H2XeO6 + H= HXeO6- + H2O+ O22and the hydroxyl radical is involved as an intermediate.、The Stereo Structures of Xenon Comp

12、ounds1.符合 VSEPR (valence shell electron pair repulsion)理論XeF2 AB 2E3sp3d直線型XeF4 AB4E2sp3d2平面四方3XeO3 » AB3Esp二角錐型-3XeO4 » AB 4sp正四面體XeOF4 a AB5Esp3d2四方錐型XeO2F2 » AB4Esp3d歪四面體XeO4- - AB 6sp3d2正八面體2.特殊構(gòu)型F超產(chǎn)Xe?F32XeF2 AsF§ =XezFsAsFe-XeF6 The exact structure of the gaseous XeF6 molec

13、ular has not1:been determined, but it is known to be a slightly distorted octahedron(a) lone pair emerging through edge of the octahedron C2V symmetryElement Reaction Flowchart(b) lone pair emerging through face of the octahedron C3V symmetryA Flowchart is Mr xcruu the uiblc gas vith A 5埴1川艮川式 dwni

14、istrv.Bonding in Noble Gas CompoundsAs it was widely believed, prior to 1962, that the noble gases were chemically inert because of the stability, if not inviolability, of their electronic configurations, the discovery that compounds could in fact be prepared, immediately necessitated a description

15、of the bonding involved. A variety of approaches has been suggested, none of which is universally applicable. The simplest molecular-orbital description is that of the 3-centre, 4-electron o-bond in XeF2, which involves only valence shell p orbitals and eschews the use of higher energy d orbitals. T

16、he orbitals involved are the collinear set comprising the 5Px orbital of Xe, which contains 2 electrons, and the 2px orbitals from each of the F atoms, each containing 1 electron. The possible combinations of these orbitals are shown in Fig. A and yield 1 bonding, 1 nonbonding, and 1 antibonding orb

17、ital. A single bonding pair of electrons is responsible for binding all 3 atoms, and the occupation of the nonbonding orbital, situated largely on the F atoms, implies significant ionic character. The scheme should be compared with the 3-centre, 2-electron bonding proposed for boron hydrides.A simil

18、ar treatment, involving two 3-centre bonds accounts satisfactorily for the planar structure of XeF4 but fails when applied to XeF6 since three 3-centre bonds would produce a regular octahedron instead of the distorted structure actually found. An improvement is possible if involvement of the Xe 5d o

19、rbitals in invoked, since this produces a triplet level which would be subject to a Jahn-Teller distortion. However, the approach which as most consistently rationalized the stereochemistries of noble-gas compounds (as distinct from their bonding) is the electron-pair repulsion theory of Gillespie a

20、nd Nyholm. This assumes that stereochemistry is determined by the repulsions between valence-shell electron-pairs, both nonbonding and bonding, and that the former exert the stronger effect. Thus, in XeF 2 the Xe is surrounded by 10 electrons (8 from Xe and 1 from each F) distributed in 5 pairs; 2 b

21、onding and 3 nonbonding. The 5 pairs are directed to the corners of a trigonal bipyramid and, because of their greater mutual repulsions, the 3 nonbonding pairs are situated in the equatorial plane at 120 to each other, leaving the 2 bonding pairs perpendicular to the plane and so producing a linear F-Xe-F molecule.In the same way XeF4, with 6 electron-pairs, is considered as pseudo-octahedral with its 2 nonbonding pairs trans to each other, leaving the 4 F atoms in a plane around the Xe. More distinctively, The 7 electron-pairs of XeF6 suggest the possibility of a non-regular oc