Hydrides H₂E (E = S, Se, Te)

  Selected physical data for hydrogen sulfide, selenide and telluride are listed in Table 1.1 and illustrated in Figures 9.6 and 9.7. Hydrogen sulfide is more toxic that HCN, but because H₂S has a very characteristic odour of rotten eggs, its presence is easily detected. It is a natural product of decaying S-containing matter, and is present in coal pits, gas wells and sulfur springs. Where it occurs in natural gas deposits, H₂S is removed by reversible absorption in a solution of an organic base and is converted to S by controlled oxidation. Figure 15.2 showed the increasing importance of sulfur recovery from natural gas as a source of commercial sulfur. In the laboratory, H₂S was historically prepared by reaction 1.1 in a Kipp’s apparatus. The hydrolysis of calcium or barium sulfides (e.g. equation 1.2) produces purer H₂S, but the gas is also commercially available in small cylinders.

                     (1.1)

                              (1.2)

Hydrogen selenide may be prepared by reaction 1.3, and a

similar reaction can be used to make H2Te.

                          (1.3)

    The enthalpies of formation of H₂S, H₂Se and H₂Ten (Table 1.1) indicate that the sulfide can be prepared by direct combination of H₂ and sulfur (boiling), and is more stable with respect to decomposition into its elements than H₂Se or H₂Te. Like H₂O, the hydrides of the later elements in group 16 have bent structures but the angles of ≈ 90^o (Table 1.1) are significantly less than that in H₂O (105⁰). This suggests that the E^_H bonds (E= S, Se or Te) involve p character from the central atom (i.e. little or no contribution from the valence s orbital). In aqueous solution, the hydrides behave as weak acids (Table 1.1 ).

Table 1.1 Selected data for H₂S, H₂Se and H₂Te.

The second ionization constant of H₂S is ≈ 10^-19 and, thus, metal sulfides are hydrolysed in aqueous solution. The only reason that many metal sulfides

can be isolated by the action of H₂S on solutions of their salts is that the sulfides are extremely insoluble. For example, a qualitative test for H₂S is its reaction with aqueous lead acetate (equation 1.4).

               (1.3)

    Sulfides such as CuS, PbS, HgS, CdS, Bi₂S₃, As₂S₃, Sb₂S₃ and SnS have solubility products less than ≈10^-30 and can be precipitated by H₂S in the presence of dilute HCl. The acid suppresses ionization of H₂S, lowering the concentration of S^2- in solution.  Sulfides such as ZnS, MnS, NiS and CoS with solubility products in the range ≈ 10^-15  to 10^-30 are precipitated only from neutral or alkaline solutions.  Protonation of H₂S to [H₃S]⁺‏ can be achieved using the superacid HF/SbF₅.   The salt [H₃S][SbF₆] is a white crystalline solid which reacts with quartz glass; vibrational spectroscopic data for [H₃S]⁺‏ are consistent with a trigonal pyramidal structure like that of [H₃O]⁺.  The addition of MeSCl to [H₃S][SbF₆] at 77K followed by warming of the mixture to 213K yields [Me₃S][SbF₆], which is stable below 263 K. Spectroscopic data (NMR, IR and Raman) are consistent with the presence of the trigonal pyramidal [Me₃S]‏ cation.

مواضيع ذات صلة

تطبيق ثلاثيات العدد الذري على المجموعة ٣

تطبيق نفس المعيار على عناصر أخرى يصعب تسكينها في أماكن مناسبة

معيار جديد: الحفاظ على الثلاثيات أو ابتكار ثلاثيات جديدة

بعض الحالات الخاصة

أنماط الجدول الدوري

كيميائية العناصر التخليقية

العناصر من ١١٣ إلى ١١٨

العنصر ١٠٧ وما بعده

العناصر من ١٠١ إلى ١٠٦

عناصر ما بعد اليورانيوم الحقيقية

العناصر الناقصة

الخيمياء الحديثة: من عناصر ناقصة إلى عناصر تخليقية