Molecular hydrogen melting temperature

For ice Ih, at the melting temperature, Ty =10 s and tj, = 10" s. In contrast, in water, owing to the disorder of the liquid phase the two times are Xy = 2-3x10 s and Td = 1.8x10" s, respectively. The mean lifetime of the hydrogen bond tiq assumes values interme ate between the characteristic time of structure V and structure D (thb = 9x10" s). We aim to describe the dynamic properties of water in structure D, by means of a theory that can account for diffusional phenomena in the different molecular environments to do this we shall have to apply suitable time-average procedures to processes the time scale of which is shorter than Thb-... 

In general, except in ice, molecules in molecular crystals are packed together as closely as their size and shape allow. Because van der Waals forces and hydrogen bonding are generally quite weak compared with covalent and ionic bonds, molecular crystals are more easily broken apart than ionic and covalent crystals. Indeed, most molecular crystals melt at temperatures below 100°C. 

In a simple molecular solid, such as iodine (y or ice, the vibrating particles are molecules which are held by weak van der Waals or hydrogen bonding forces of attraction, and so the solid has a low melting temperature. 

Elemental hydrogen exists at room temperature as a colorless, odorless, tasteless gas composed of diatomic molecules. We can call H2 dthydrogen, but it is more commonly referred to as either molecular hydrogen or simply hydrogen. Because H2 is nonpolar and has only two electrons, attractive forces between molecules are extremely weak. As a result, its melting point (—259 °C) and boiling point (—253 °C) are very low. 

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