The alkali metals a summary of their atomic and physical properties

Element (allotrope) Temperature range/°C Crystal structure Fattice parameters/pm Atomic volume, iyio6pm3 Molar volume/ cmVmol Density/ g/cm3 

The alkali metals are soft and have a high lustre when freshly cut. Lithium is the least fusible and volatile, the least dense and soft. The values of these properties change regularly down the 1st column of the Periodic Table. Notice, however, the trend of the density. 

Their normal crystal structure, at ambient conditions, corresponds to the body-centred cubic cI2-W-type structure. At very low temperatures, the close-packed hexagonal hP2-Mg-type structure has been observed for Li and Na, while for Rb and Cs the face-centred cubic close-packed cF4-Cu-type structure is known at high pressure. No polymorphic transformation has been reported for potassium. 

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