H2 S(硫化氫) 同SiH4(甲矽烷) 那一個沸點較高

1. The central atom S has two bond pairs and two lone pairs. It should adopt a v-shaped but not linear shape. So it has a bond angle similar to H2O.
i.e. The bond angle of H2S may still vary with H2O due to other kinds of reasons, like bonding structure and hybridization etc.

2. H2S has a simple molecular structure while SiH4 has a giant covalent structure. So H2S molecules are just held by weak van der Waals' forces but the atoms in SiH4 are held by strong covalent bonds, more energy is required to break the atoms in SiH4 rather than the molecules between the H2S. The boiling point of SiH4 is much higher than H2S.

2011-09-30 19:04:33 補充：
Amendment:
Both SiH4 and H2S have a simple molecular structure. However, H2S molecule is sparingly polar because the dipole moments cannot cancel out each other. SiH4 molecule is non-polar because it is arranged symmetrically and the dipole moments all cancel out each other.

2011-09-30 19:07:00 補充：
Therefore, H2S molecules are held by stronger dipole-dipole interactions in addition of weak instantaneous dipole-induced dipole interactions. But SiH4 are just held by weak instantaneous dipole-induced dipole interactions. The boiling pt H2S is higher than SiH4.

2011-09-30 19:07:45 補充：
i.e. their molecular size is quite similar so that the comparison is fair enough.

Thank you for 小云's reminder.

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SiH4 should have simple molecular structure