第二十章鑭系元素和錒系元素

1、278第二十章 鑭系元素和錒系元素Chapter 20 The Lanthanides and Actinides鑭系元素La、 Ce、 Pr、 Nd、 Pm、 Sm、 Eu、 Gd、 Tb、 Dy、 Ho、 Er、 Tm、 Yb、 Lu(鑭) (鈰) (鐠) (釹) (钷) (釤) (銪) (釓) (鋱) (鏑) (鈥) (鉺) (銩 )(鐿) (镥)錒系元素Ac、 Th、 Pa、 U、 Np、

2、 Pu、 Am、 Cm、 Bk、 Cf、 Es、 Fm、 Md、 No、 Lr(錒) (釷) (鏷) (鈾) (镎) (钚) (镅) (鋦) (锫) (锎) (锿) (鐨) (鍆) (锘) (鐒)§20-1 鑭系元素（ 系元素（Ln）The Lanthanides一、General Properties：1．鑭系元素 從 57 號(hào)元素鑭到第 71 號(hào)元素镥，共十五種元素，稱為鑭系元素，用 Ln表示。2．稀土元素 周

3、期表 ⅢB 族中的鈧（Sc）、釔（Y）和鑭系元素在性質(zhì)上都非常相似并在礦物中共生，由于鑭系收縮，Y3+離子的半徑落在 Er3+附近，Sc3+離子的半徑接近于Lu3+，所以 Sc、Y 可以看作鑭系元素的成員。在化學(xué)上把 Sc、Y 和鑭系元素統(tǒng)稱為稀土元素（rare earth’s elements），用 RE 表示。3．Oxidation states （以+3 為特征氧化態(tài)，其他還有+2 或+4 氧化態(tài)）4f 6、4f 7

4、 4f 13、4f 14Sm2+、Eu2+ Tm2+、Yb2+4f 0、4f 1、4f 2、4f 3、4f 4、4f 5、4f 6、4f 7、4f 8、4f 9、4f 10、4f 11、4f 12、4f 13、4f 14La3+、Ce

5、3+、Pr3+、Nd3+、Pm3+、Sm3+、Eu3+、Gd3+、Tb3+、Dy3+、Ho3+、Er3+、Tm3+、Yb3+、Lu3+4f 0、4f 1 4f 7、4f 8Ce4+、Pr4+ Tb3+、Dy3+

6、溶液中能穩(wěn)定存在的氧化態(tài)有：Ln3+、Eu2+(4f 7)、Yb2+(4f 14)、Ce(IV)(4f 0)4．原子半徑和離子半徑(1) 鑭系收縮 鑭系元素的原子半徑和離子半徑在總的趨勢(shì)上都是隨著原子序數(shù)的增加而逐漸地縮小，這種原子半徑依次縮小的積累，稱為鑭系收縮。(2) 鑭系收縮的影響(a) Sc、Y 與鑭系元素共生；(b) Zr、Hf，Nb、Ta，Mo、W，Tc、Re 在原子半徑上非常接近，造成分離極其困難。5．離子的顏色(1) 電

7、子構(gòu)型全空，半滿和全滿，或接近全空，半滿和全滿的 4f 電子的離子是穩(wěn)定的或比較穩(wěn)定，難以實(shí)現(xiàn) 4f 電子激發(fā)，故是無(wú)色的?！?La3+ (4f 0 )、Gd3+ (4f 7 )、Lu3+ (4f 14 )、Ce3+ (4f 1 )、Eu3+ (4f 6 )、Tb3+ (4f 8 )、Yb3+ (4f 13 )都是無(wú)色(2) 具有 4f x和 4f 14?x的+3 價(jià)離子顯示的顏色相同或相近。280U3O8不溶于水，但溶于酸，生成 。

8、? 2 2 UO二、硝酸鈾酰[UO2(NO3)2] 1. Preparation UO3 + 2HNO3 UO2(NO3)2 + H2O2. Properties 水解生成 ? ? ?5 3 22 2 2 2 2 (OH) ) (UO (OH) ) UO ( (OH) UO 、 、加堿生成 Na2U2O7·6H2O（黃色），加熱脫水，生成無(wú)水 Na2U2O7，俗稱鈾黃。3. Structure UO2(N

9、O3)2·2H2O（六角雙錐）三、UF6（八面體）1. Preparation UO3 + 3SF4 UF6 + 3SOF2300¡æ2. Hydrolysis UF6 + 2H2O UO2F2 + 4HFSuperconductivityH. Kammerling Onnes (Nobel Prize for Physics, 1913) discovered superconductivit

10、y in Leiden in 1911 when he cooled mercury to the temperature of liquid helium; Many other materials, mostly metals and alloys, were subsequently found to display superconductivity at very low temperatures.Two properties

11、 characterize a superconductor:1. It is perfectly conducting, i.e. it has zero resistance.2. It is perfectly diamagnetic, i.e. it completely excludes applied magnetic fields. This is the Meissner effect and is the reason

12、 why a superconductor can levitate a magnet. Superconductivity exists within the boundaries of three limiting parameters which must not be exceeded：the critical temperature (Tc), the critical magnetic field (Hc) and the

13、critical current density (Jc).Until 1986 the highest recorded value of Tc was ~23K for Nb3Ge but in that year Bednorz and Muller, in pioneering work for which they received the 1987 Nobel Prize for Physics, reported Tc=

14、30K in an entirely new Ba-La-Cu-O ceramic system quickly identified as La2-xBaxCuO4.This prompted an examination of other Cu-O systems and the technologically important breakthrough in 1987 by the Houston and Alabama tea

15、ms of C.W. Chu and M. K. Wu, of superconductivity at temperatures attainable in liquid nitrogen, Tc=95K in a material subsequently shown to be YBa2Cu3O7, “YBCO“. This , and other materials in which Y is replaced by a lan

16、thanide, are referred to as “1,2,3“ materials because of their stoichiometry. This produced a quite unprecedented explosion of activity amongst chemists, physicists and material scientists around the world. Though the hi

17、ghest Tc has been pushed up to 135K (or 164 K under 350 kbar pressure) in HgBa2Ca2Cu3O8, YBCO is still the archetypal high temperature superconductor. In spite of its long history, it was not until 1957 that Bardeen, Coo

18、per and Schrieffer provided a satisfactory explanation of superconductivity.This “BSC: theory“ suggests that pairs of electrons (Cooper pairs) move together through. the lattice, the first electron polarizing the lattice

19、 in such a way that the second one can more easily follow it. The stronger the interaction of the two electrons the higher Tc, but it turns out as a consequence of this model that Tc should have an upper limit ～35K. The