 Xenon has atomic number 54 ; that is , its nucleus contains 54 protons . At standard temperature and pressure , pure xenon gas has a density of 5 @.@ 761 kg / m3 , about 4 @.@ 5 times the surface density of the Earth 's atmosphere , 1 @.@ 217 kg / m3 . As a liquid , xenon has a density of up to 3 @.@ 100 g / <unk> , with the density maximum occurring at the triple point . Notably , liquid xenon has a high <unk> due to its large atomic volume , and thus is an excellent solvent . It can dissolve <unk> , biological molecules , and even water . Under the same conditions , the density of solid xenon , 3 @.@ 640 g / cm3 , is higher than the average density of granite , 2 @.@ 75 g / cm3 . Using <unk> of pressure , xenon has been forced into a metallic phase . 
