第二十章 鑭系、錒系元素和核化學(xué)(

1、第二十章鑭系元素和錒系元素Chapter 20The 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、 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(LnThe Lanthanides一、General Properties:1.鑭系元素從5

2、7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.稀土元素周期表B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(r are earths 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 4f 13、4f 14Sm2+、Eu2+ Tm2+、Yb2+4f 0、4f 1、4f 2、4f 3、4f 4、4f 5、4f

3、6、4f 7、4f 8、4f 9、4f 10、4f 11、4f 12、4f 13、4f 14 La3+、Ce3+、Pr3+、Nd3+、Pm3+、Sm3+、Eu3+、Gd3+、Tb3+、Dy3+、Ho3+、Er3+、Tm3+、Yb3+、Lu3+4f 0、4f 1 4f 7、4f 8Ce4+、Pr4+ Tb3+、Dy3+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 04.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 S

4、c、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。(3 f 電子相同,離子電荷不同的離子,其顏色不同。Ce 4+ (4f 0 橙紅 Sm 2+ (4f 6

5、 淺紅 Eu 2+ (4f 7 草黃 Yb 2+ (4f 14 綠6.標(biāo)準(zhǔn)還原電位(1 /Ln Ln 3+很負(fù),而且與pH 無(wú)關(guān),所以不管在H +或OH -介質(zhì)中,鑭系元素都是較 強(qiáng)的還原劑。 (2 (IV343Ce /Ce 24 1.70 V (1M HClO 1.61 V (1M HNO 1.44 V (1M H SO 1.28 V ( 2M HCl +=+在中,在中在中,在中 這說(shuō)明Ce (IV在HClO 4中不形成配離子,而在HNO 3、H 2SO 4、HCl 中都不同程度地形成配離子。7.+4 O.S.只有Ce (IV在水溶液中是最穩(wěn)定的,由于Ce 3+是鈰的特征氧化態(tài),所以Ce (

6、IV是強(qiáng)氧化劑。Ce (IV與NaOH 反應(yīng),生成Ce(OH3(黃色并放出O 24Ce(NO 34 + 16NaOH 4Ce(OH3 + 16NaNO 3 + O 2 + 2H 2OCeO 2與H 2SO 4反應(yīng),同樣放出氧氣4CeO 2 + 6H 2SO 42Ce 2(SO 43 + O 2+ 6H 2OCeO 2與鹽酸反應(yīng),放出氯氣2CeO 2 + 8HCl 2CeCl 3 + Cl 2+ 4H 2O8.鑭系元素氫氧化物L(fēng)n(OH3的堿性接近堿土金屬氫氧化物的堿性,但溶解度較堿土金屬氫氧化物小。Ln(OH3的堿性隨Ln 3+離子的半徑的遞減而有規(guī)律的減小。 由 = Z / r 或知,從La

7、 3+ Lu 3+的離子半徑減小, 增大, M -O 鍵增強(qiáng),因此,鑭系元素氫氧化物的堿式電離從La(OH3到Lu(OH3是減小的。§20-2 錒系元素The Actinides我們只介紹鈾及其化合物的性質(zhì)。鈾的重要化合物 UO 2(暗棕色 U 3O 8(墨綠色 UO 3(橙黃色一、鈾的氧化物1.UO 3(1 amphoteric oxide UOUO 2+2U 2O 2 7 (2 decomposition 2UO 32UO 2 + O 2 (3 preparation 2UO 2(NO 32 2UO 3 + 4NO 2 + O 22.U 3O 8 preparation :3U(

8、C 2O 42U 3O 8 + 8CO + 4CO 2 或者:3U + 4O2 U 3O 8 U 3O 8不溶于水,但溶于酸,生成+22UO 。二、硝酸鈾酰UO 2(NO 321. Preparation UO 3 + 2HNO 3UO 2(NO 32 + H 2O2. Properties 水解生成+53222222(OH(UO (OHUO ( (OHUO 、 加堿生成Na 2U 2O 7·6H 2O (黃色,加熱脫水,生成無(wú)水Na 2U 2O 7,俗稱鈾黃。3. Structure UO 2(NO 32·2H 2O (六角雙錐三、UF 6(八面體 1. Preparat

9、ion UO 3 + 3SF 4300UF 6 + 3SOF 2 2. Hydrolysis UF 6 + 2H 2OUO 2F 2 + 4HFSuperconductivityH. Kammerling Onnes (Nobel Prize for Physics, 1913 discovered superconductivity in Leiden in 1911 when he cooled mercury to the temperature of liquid helium; Many other materials, mostly metals and alloys, were

10、subsequently found to display superconductivity at very low temperatures.Two properties 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

11、 reason why a superconductor can levitate a magnet.Superconductivity exists within the boundaries of three limiting parameters which must not be exceeded :the critical temperature (T c, the critical magnetic field (H c and the critical current density (J c.Until 1986 the highest recorded value of T

12、c was 23K for Nb 3Ge but in that year Bednorz and Muller, in pioneering work for which they received the 1987 Nobel Prize for Physics, reported T c=30K in an entirely new Ba-La-Cu-O ceramic system quickly identified as La 2-x Ba x CuO 4.This prompted an examination of other Cu-O systems and the tech

13、nologically important breakthrough in 1987 by the Houston and Alabama teams of C.W. Chu and M. K. Wu, of superconductivity at temperatures attainable in liquid nitrogen, T c=95K in a material subsequently shown to be YBa 2Cu 3O 7, “YBCO". This , and other materials in which Y is replaced by a l

14、anthanide, 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 highest T c has been pushed up to 135K (or 164 K under 350 kbar pressu

15、re in HgBa 2Ca 2Cu 3O 8, YBCO is still the archetypal high temperature superconductor.In spite of its long history, it was not until 1957 that Bardeen, Cooper 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 in such a way that the second one can more easily follow it. The stronger the interaction of the two electrons the higher T c, but it turns out as a consequence of this model that T c