Hydrides H2E E S, Se, Te

Selected physical data for hydrogen sulfide, selenide and telluride are listed in Table 16.4 and illustrated in Figs. 10.7 and 10.8. Hydrogen sulfide is more toxic than HCN, but because H2S has a very characteristic odour of rotten eggs, its presence is easily detected. It is a natural 

Hydrogen selenide may be prepared by reaction 16.39, and a similar reaction can be used to make H2Te. 

The enthalpies of formation of H2S, H2Se and H2Te (Table 16.4) indicate that the sulfide can be prepared by direct combination of H2 and sulfur (boiUng), 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° (Table 16.4) are significantly less than that in H2O (105°). 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 16.4 and Section 7.5). The second acid dissociation constant of H2S is 10 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 

Sulfides such as CuS, PbS, HgS, CdS, BizSs, AS2S3, SbjS3 and SnS have solubility products (see Sections 6.9 and 6.10) less than and can be precipitated by H2S in 

Name Hydrogen sulfide Hydrogen selenide Hydrogen telluride 

Physical appearance and Colourless gas offensive Colourless gas offensive Colourless gas offensive 

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