第二十章镧系元素和锕系元素 Chapter 20 The lanthanides and actinides 镧系元素 La、Ce、Pr、Nd、Pm、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb、Lu (镧)(铈)(镨)(钕)(钷)(钐)(铕)(钆)(铽)(镝)(钬)(铒)(铥)镱)(镥) 锕系元素 Ac、Th、Pa、U、Np、Pu、Am、Cm、Bk、Cf、Es、Fm、Md、No、Lr (锕)(钍)(镤)(铀)(镎)(钚)(镅)(锔)(锫)(锎)(锿)(镄)(钔)(锘)(铹) §20-1镧系元素(Ln) The lanthanides General Properties: 1.镧系元素从57号元素镧到第71号元素镥,共十五种元素,称为镧系元素,用Ln 表示。 2.稀土元素周期表ⅢB族中的钪(Sc)、钇(Y)和镧系元素在性质上都非常相似并 在矿物中共生,由于镧系收缩,Y3离子的半径落在Er3附近,Sc3+离子的半径接近于 Lu3+,所以Sc、Y可以看作镧系元素的成员。在化学上把Sc、Y和镧系元素统称为 稀土元素( rare earth' s elements),用RE表示 3. Oxidation states(以+3为特征氧化态,其他还有+2或+4氧化态) f0、4fl、4f2、4f3、4f-、4f5、4f6、4f7、4f8、4r”、4fl0、41 La”、Ce”、Pr、Nd、Pm3”、Sm3”、Eur3、Gd、Tb”、Dy3、Ho3、Er”、Tm2”、Yb3、Lu 溶液中能稳定存在的氧化态有:Ln3、Eu2(4f)、Yb2(4f4)、ce"Y(4f°) 4.原子半径和离子半径 1)镧系收缩镧系元素的原子半径和离子半径在总的趋势上都是随着原子序数的增 加而逐渐地缩小,这种原子半径依次缩小的积累,称为镧系收缩 (2)镧系收缩的影响 (a)Sc、Y与镧系元素共生 (b)Zr、Hf,Nb、Ta,Mo、W,Te、Re在原子半径上非常接近,造成分离极其困 难 5.离子的颜色 1)电子构型全空,半满和全满,或接近全空,半满和全满的4电子的离子是稳定的 或比较稳定,难以实现4f电子激发,故是无色的 La3+(4f°)、Gd+(4f7)、Lu3+(4fl4)、Ce3+(4fl)、Eu3+(4f6)、Tb(4f8)、 Yb3+(4f13)都是无色 (2)具有4fx和4f14的+3价离子显示的颜色相同或相近
278 第二十章 镧系元素和锕系元素 Chapter 20 The Lanthanides and Actinides 镧系元素 La、 Ce、 Pr、 Nd、 Pm、 Sm、 Eu、 Gd、 Tb、 Dy、 Ho、 Er、 Tm、 Yb、 Lu (镧) (铈) (镨) (钕) (钷) (钐) (铕) (钆) (铽) (镝) (钬) (铒) (铥 )(镱) (镥) 锕系元素 Ac、 Th、 Pa、 U、 Np、 Pu、 Am、 Cm、 Bk、 Cf、 Es、 Fm、 Md、 No、 Lr (锕) (钍) (镤) (铀) (镎) (钚) (镅) (锔) (锫) (锎) (锿) (镄) (钔) (锘) (铹) §20-1 镧系元素（Ln） The Lanthanides 一、General Properties： 1．镧系元素 从 57 号元素镧到第 71 号元素镥，共十五种元素，称为镧系元素，用 Ln 表示。 2．稀土元素 周期表 ⅢB 族中的钪（Sc）、钇（Y）和镧系元素在性质上都非常相似并 在矿物中共生，由于镧系收缩，Y3+离子的半径落在 Er3+附近，Sc3+离子的半径接近于 Lu3+，所以 Sc、Y 可以看作镧系元素的成员。在化学上把 Sc、Y 和镧系元素统称为 稀土元素（rare earth’s elements），用 RE 表示。 3．Oxidation states （以+3 为特征氧化态，其他还有+2 或+4 氧化态） 4f 6、4f 7 4f 13、4f 14 Sm2+、Eu2+ Tm2+、Yb 2+ 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 14 La3+、Ce3+、Pr3+、Nd3+、Pm3+、Sm3+、Eu3+、Gd3+、Tb3+、Dy3+、Ho3+、Er3+、Tm3+、Yb 3+、Lu3+ 4f 0、4f 1 4f 7、4f 8 Ce4+、Pr4+ Tb3+、Dy3+ 溶液中能稳定存在的氧化态有：Ln3+、Eu 2+(4f 7 )、Yb2+(4f 14)、Ce(IV)(4f 0 ) 4．原子半径和离子半径 (1) 镧系收缩 镧系元素的原子半径和离子半径在总的趋势上都是随着原子序数的增 加而逐渐地缩小，这种原子半径依次缩小的积累，称为镧系收缩。 (2) 镧系收缩的影响 (a) Sc、Y 与镧系元素共生； (b) Zr、Hf，Nb、Ta，Mo、W，Tc、Re 在原子半径上非常接近，造成分离极其困 难。 5．离子的颜色 (1) 电子构型全空，半满和全满，或接近全空，半满和全满的 4f 电子的离子是稳定的 或比较稳定，难以实现 4f 电子激发，故是无色的。 ∴ La3+ (4f 0 )、Gd3+ (4f 7 )、Lu3+ (4f 14 )、Ce3+ (4f 1 )、Eu3+ (4f 6 )、Tb3+ (4f 8 )、 Yb3+ (4f 13 )都是无色 (2) 具有 4f x和 4f 14−x的+3 价离子显示的颜色相同或相近
(3)f电子相同,离子电荷不同的离子,其颜色不同 Ce(4f)橙红Sm2+(4f6)浅红Eu2(4f7)草黄Yb2+(4f14)绿 6.标准还原电位 (1)q12n很负,而且与pH无关,所以不管在H或OH介质中,镧系元素都是较 强的还原剂 cya,=+10V(在MHCO中+161V(在MHNO中) +144V(在MHSO中+128V(在MHC中 这说明Ce在HCO4中不形成配离子,而在HNO3、H2SO4、HC1中都不同 程度地形成配离子 7.[+4]0.S 只有Ce)在水溶液中是最稳定的,由于Ce3+是铈的特征氧化态,所以Ce是 强氧化剂。 Ce与NaOH反应,生成Ce(OH)3↓(黄色)并放出O2 4Ce(NO3 )4+ 16NaoH- 4Ce(OH)3++ 16NaNO3+O2+2H20 CeO2与H2SO4反应,同样放出氧气 4Ce0+6H2SO4 Ce2(SO4)3+O2↑+6H2O CeO2与盐酸反应,放出氯气 2Ce0+8HCI- 2CeCl3 +Cl2 t+4H,O 8.镧系元素氢氧化物Ln(OH)3的碱性接近碱土金属氢氧化物的碱性,但溶解度较碱土金 属氢氧化物小 Ln(OH)3的碱性随Ln3离子的半径的递减而有规律的减小 ∵由φ=Z/r或知,从La3*→Lu3的离子半径减小,φ增大,∴M-O键增强,因 此,镧系元素氢氧化物的碱式电离从La(OH)3到LuOH)3是减小的。 §20-2锕系元素 The actinides 我们只介绍铀及其化合物的性质 铀的重要化合物UO2(暗棕色)U3O8(墨绿色)UO3(橙黄色) 铀的氧化物 1.UO3 1)amphoteric oxide UO3/ U201 (2)dec △2UO2 (3)preparation 2UO(NO3)242UO3+ 4NO2+O preparation: 3U(C204)24 U308+8CO+ 4C02 或者:3U+402=U3O3 U3O不溶于水,但溶于酸,生成UO2
279 (3) f 电子相同，离子电荷不同的离子，其颜色不同。 Ce4+ (4f 0 ) 橙红 Sm2+ (4f 6 ) 浅红 Eu2+ (4f 7 ) 草黄 Yb2+ (4f 14 ) 绿 6．标准还原电位 (1) Ln /Ln 3+ 很负，而且与 pH 无关，所以不管在 H+或 OH－介质中，镧系元素都是较 强的还原剂。 (2) (IV) 3 4 3 Ce / Ce 2 4 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 这说明 Ce(IV)在 HClO4 中不形成配离子，而在 HNO3、H2SO4、HCl 中都不同 程度地形成配离子。 7．[+4] O.S. 只有 Ce(IV)在水溶液中是最稳定的，由于 Ce3+是铈的特征氧化态，所以 Ce(IV)是 强氧化剂。 Ce(IV)与 NaOH 反应，生成 Ce(OH)3↓（黄色）并放出 O2 4Ce(NO3)4 + 16NaOH 4Ce(OH)3↓ + 16NaNO3 + O2 + 2H2O CeO2 与 H2SO4 反应，同样放出氧气 4CeO2 + 6H2SO4 2Ce2(SO4)3 + O2↑+ 6H2O CeO2 与盐酸反应，放出氯气 2CeO2 + 8HCl 2CeCl3 + Cl2↑+ 4H2O 8．镧系元素氢氧化物 Ln(OH)3 的碱性接近碱土金属氢氧化物的碱性，但溶解度较碱土金 属氢氧化物小。 Ln(OH)3 的碱性随 Ln3+离子的半径的递减而有规律的减小。 ∵ 由 = Z / r 或知，从 La3+ → Lu3+的离子半径减小， 增大，∴ M－O 键增强，因 此，镧系元素氢氧化物的碱式电离从 La(OH)3 到 Lu(OH)3 是减小的。 §20-2 锕系元素 The Actinides 我们只介绍铀及其化合物的性质。 铀的重要化合物 UO2（暗棕色） U3O8（墨绿色） UO3（橙黄色） 一、铀的氧化物 1．UO3 (1) amphoteric oxide UO3 H + UO 2+ 2 U2O 2 7 OH (2) decomposition 2UO3 2UO2 + O2 (3) preparation 2UO2(NO3)2 2UO3 + 4NO2 + O2 2．U3O8 preparation：3U(C2O4)2 U3O8 + 8CO + 4CO2 或者：3U + 4O2 U3O8 U3O8 不溶于水，但溶于酸，生成 2+ UO2
二、硝酸铀酰[UO2(NO)} Preparation UO3 + 2HNO UO2(NO3 )2+ H2O 2. Properties水解生成UO2(OH)+、(UO2)2(OH2、(UO2)3OH 加碱生成NaU2O6H2O(黄色),加热脱水,生成无水NaU2O7,俗称铀黄。 3. Structure Uo2(NO3)22H2O(六角双锥) H UF6(八面体) O -O- -O-H 1. Preparation UO + 3SF4 UF6+ 3SOF 2. Hydrolysis UF6+2H20- UO2 F2+ 4HF H0- of UO2(NO3 )2 2H20 Superconductivity H 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 subsequently found to display superconductivity at very low 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 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(Tc), the critical magnetic field (Hc)and the critical current Until 1986 the highest recorded value of Tc was -23K for Nb Ge but in that year Bedn nd Muller, in pioneering work for which they received the 1987 Nobel Prize for Physics, reported Tc=30K in an entirely new Ba-La-Cu-O ceramic system quickly identified as Laz- Ba- CuO4. This prompted an examination of other Cu-O systems and the technologically 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, Tc=95K in a material subsequently shown to be YBa2 Cu3 O7, "YBCO". This, and other materials in which Y is replaced by a lanthanide, are referred to as"1, 2, 3 materials because of their stoichiometry. This produced a quite the world. Though the highest Tc has been pushed up to 135K(or 164 K under 350 kbar pressure) in Hg Ca Cu3O8, 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 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 Tc, but it turns out as a consequence of this model that Tc should have an upper limit 35K. The advent of high-temperature superconductors therefore necessitated a new, or at least modified, explanation for the pairing, mechanism. Various suggestions have been made but none has yet gained universal acceptance 280
280 二、硝酸铀酰[UO2(NO3)2] 1. Preparation UO3 + 2HNO3 UO2(NO3)2 + H2O 2. Properties 水解生成 + + + 2 3 5 2 2 2 2 2 UO (OH) 、 (UO ) (OH) 、(UO ) (OH) 加碱生成 Na2U2O7·6H2O（黄色），加热脱水，生成无水 Na2U2O7，俗称铀黄。 3. Structure UO2(NO3)2·2H2O（六角双锥） 三、UF6（八面体） 1. Preparation UO3 + 3SF4 300℃ UF6 + 3SOF2 2. Hydrolysis UF6 + 2H2O UO2F2 + 4HF Superconductivity H. 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 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 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 (Tc), the critical magnetic field (Hc) and the 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=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 teams 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 lanthanide, 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 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, 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 Tc, but it turns out as a consequence of this model that Tc should have an upper limit ～ 35K. The advent of high-temperature superconductors therefore necessitated a new, or at least modified, explanation for the pairing, mechanism. Various suggestions have been made but none has yet gained universal acceptance. O O O O O O H H H N O H N O U O O Fig. 20.1 The structure of UO2(NO3)2·2H2O