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Group IIB (12) (p267)

Group IIB (12) (p267). Zinc Cadmium Mercury. Introduction (p267). Electronic configuration: (n-1)d 10 ns 2 np 0 Metallic: form +2 cation Electronic configuration of +2 ions: (n-1)d 10 , which makes the ions: smaller radius larger polarizability

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Group IIB (12) (p267)

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  1. Group IIB (12) (p267) Zinc Cadmium Mercury

  2. Introduction (p267) • Electronic configuration: (n-1)d10ns2np0 • Metallic: form +2 cation • Electronic configuration of +2 ions: (n-1)d10, which makes the ions: smaller radius larger polarizability Their properties are very different from those of the ions of IIA. Zn likes Be or Mg in some way. than the ions of group IIA

  3. Introduction (p267) • Metallic reactivity decreases from top to bottom: E°(M2+/M) = –0.76, –0.40, 0.85 • Zinc and cadmium are similar, but mercury Why ? 4f14; the enthalpy of hydration of +2 ions • Univalent state important for Hg, metal-metal bond M─M • Coordination compounds

  4. Occurrence, Isolation, and Properties of the Elements (p267) • Relatively low abundance, but easily obtained • ZnS(Fe, Pb), CdS and HgS • Roasting, which gives the oxides • Reduced by carbon • Distillation or electrolysis • Elements, volatile. Hg, liquid. Why ?

  5. Properties of the Elements (p268) • Zinc and Cadmium react with • most nonmetallic elements (under some conditions), but H2, N2, or C • Acids • Bases only with Zn Why ? Amphoteric • Mercury react with • Oxygen and Sulphur • Oxidizing acids

  6. Properties of the Elements (p268) • Alloy: brass • Amalgam: liquid or solid, Na, Ag, Au, but Fe • Toxicity : Cd2+ can replaces Zn2+ in some enzymes Hg, moderate, but when converted into CH3Hg+ by bacteria, exceedingly toxic, because it can combine with S atom in biomolecules

  7. The univalent state • Important for mercury • HgI–HgII Equilibria: Hg2+ Hg22+ Hg ε= 0.131 V E(Hg2+/Hg) = 0.854 V K = 6E–3 for the disproportionation • No common oxidizing reagent has a standard potential between -0.79 and -0.85 V, so Hg Hg2+. How is Hg22+ preparated ? 0.920 0.797

  8. The univalent state • Factor effecting disproportionation: • Precipitating agent: hydroxide, sulfide, ammonia; halides but fluoride • Complexing agent: cyanide, halides but fluoride

  9. Oxides (p270, 271) • ZnO, amphoteric, white to yellow • CdO, basic, greenish yellow to brown to nearly black, depending on its thermal history as ZnO Lattice defects • HgO, amphoteric but more basic, red or yellow, depending on its particle size as Ag • Zn(OH)2 and Ca(OH)2, no Hg(OH)2

  10. Sulfides (p270, 271) • ZnS, white, wurtzite Or zinc blende structure; ZnS·BaSO4 • CdS, yellow • Both base materials for optical • HgS, black or red, can dissolve in S2– aqueous solution

  11. Halides (p270, 271) • Fluorides, ionic • The other halides, ionic-covalent, dissolve not only in water but also in alcohols, ketones, or similar donor solvents • HgCl2, mp: 280 ºC, liquid state is a solvent HgCl2 + HgCl2 HgCl+ + HgX3– • Hg2Cl2, electrode, light makes it diproportionation

  12. Salts (p270, 271, 272) • Hydrolysis: the solutions are acidic, Hg2+ extensively hydrolyzed, stable the ion by acidificating • ZnCl2, the most soluble solid salt in water ZnCl2 + H2O H[ZnCl2(OH)] H[ZnCl2(OH)] + FeO Fe[ZnCl2(OH)]

  13. Coordination compounds • Halides but fluoride, Hg2+ complexes, very stable Cl < Br < I; Hg > Zn > Cd • Cyanide • Ammonia • Organic ligands containing N, S, O donor atoms

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