C3-Group1-Alkali-Metals.pptx

1、Group 1 elementsAlkali metals (IA),Assigned reading materials Rayner-DIC p245-267; p156-158 Optional reading materials Rayner-DIC p253 lithium batteries; p265 11.15 biological aspects,ns1,Generalization,Metallic luster, low density, low hardness, low mp., good electric and thermal conductivity. Weak

2、er metallic bond.,Properties of simple substances,Occurrence,Na: rock salt (NaCl) seawater sylvinite (KCl/NaCl) borax (Na2B4O5(OH)48H2O) 硼砂 Chile saltpetre (NaNO3) 硝石 K: sylvite (KCl) seawater sylvinite (KCl/NaCl) carnallite (KClMgCl26H2O) 光卤石 Li, Rb, Cs: various silicate minerals, e.g. spodumene (L

3、iAlSi2O6) 锂辉石,Extraction of sodium Downs process,Extraction of potassium,Na(l) + KCl(l) K(g) + NaCl(l) At 850 C K b.p. 766 C Na b.p. 890 C,The industrial synthesis of NaOH,Typical reactions for alkali metals,Species of dioxygen,Molecular orbital energy level diagram of O22-,Why alkali metals form di

4、fferent oxides? A thermodynamic viewpoint,Why do alkali metals form different oxides? Li2O (LiO0.5) Na2O2 (NaO) KO2,The large alkali metal cations stabilize large low-charge anions. The less polarizing cations (those with low charge density) stabilize larger polarizable anions. Vice versa.,The atypi

5、cal property of lithium,Why Li is the most powerful reducing metal among the alkali metals? Which one, Li or Na, reacts with water more vigorously? Why?,The atypical property of lithium,Smaller radius results in higher hydration energy,Kinetic factors determine the chemical rates,M.p. (Li) = 180.54

6、C M.p. (Na) = 97.81 C (why) The melt metal has larger surface. LiOH is less soluble in water than NaOH. (why) (At 288K, 5.3 vs. 26.4 mol/L) The metal covered with hydroxide has smaller reaction surface.,Each Li+ has 25.3 hydrated water molecules; Hhydration = -519 kJmol-1,Flame reaction焰色反应,See also

7、: Rayner-DIC p248 Flame color,Interaction of alkali metals with ammonia,Solubility of alkali metal in ammonia (-35),Solvated electrons,Has better electric conductivity than ionic compounds in water. Less dense than liquid ammonia Dilute solution is paramagnetic; at higher concentration, less paramag

8、netic. 2 e- = e22- Blue color (broad 1500 nm) is attributed to solvated e. M+ is colorless. 5. Excellent reducing agents. NH4+ + e- = NH3 + H2 Fe(CO)5 + 2e- = Fe(CO)42- + CO,Salt solubility rule and thermodynamic explanation (Large-large and small-small),Gdissol. =Hdissol. TSdissol. Sdissol is of le

9、ss significance for dissolution of a salt. Hdissol is the main factor to affect the dissolution. Hdissol = Ucrystal +Hhydration,Conclusion: 1. rM+ rX- U prevails 2. rM+ rX- rM+ rX- Hdissol dominates,离子型盐溶解性规律,相差易溶 大对大，小对小，不易溶 大对小，小对大，较易溶 Explain why LiOH is less souble than NaOH?,Macrocyclic complex

10、es- 1987 Noble Prize in Chemistry,C.Pedersen 美国化学家 首次报道“冠醚” (crown ether),D.Cram 美国有机化学家 提出“主-客体化学” （host-guest chemistry）,J.M.Lehn 法国生物化学家 首次报道“穴醚” (cryptant),Crown ether,12-crown-4, 15-crown-5, 18-crown-6, dibenzo-18-crown-6, and diaza-18-C-6 Great affinity to alkali metals Kassoc. Depends on the

11、match between the radius of crown ether and the size of M+,In the presence of 18-crown-6 potassium permanganate dissolves in benzene “purple benzene”,18-C-6,K+,Cryptand:3-dimensional interior cavity; offer much better selectivity and strength of binding for alkali metals,Structure of 2.2.2cryptand e

12、ncapsulating a K+,2,2,1,2,2,2,Host-guest chemistry,Hard-Soft Acid-Base Concept (HSAB),(1) Hardness (a) Species with large charge to radius ratios (b) Species hard to be polarized (2) Softness (a) Species with small charge to radius ratios (b) Species easy to be polarized (3) Hard acids (metal ions) tend to bind to hard bases (ligands) - electrostatic. (4) Soft acids (metal ions) tend to bind to soft bases (ligands) - covalent.,What factors contribute to stabilize 18-C-6,K+?,Enthalpy consideration: hard acid (K+) prefers hard base (O) favorable H Entropy con