Molecular hydrides boiling temperatures

In the liquid states of some molecular hydrides, however, there is evidence that the van der Waals forces are supplemented by an additional and stronger interaction. Figure 5.11 shows the boiling temperatures of the hydrides of Groups IV-VII/14-17, and of the noble gases. 

The hydrides of sulphur, selenium and tellurium, which arc gaseous at ordinary temperatures, may be liquefied and solidified with comparative case. The boiling- and melting-points rise with increasing molecular weight ... 

Following are the melting (T ) and boiling (Tf,) temperatures of selected hydrides from Group VI of the periodic table. Explain the trends in terms of molecular structure and forces. Data from [13]. 

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