<P> In 1962, Neil Bartlett discovered the first chemical compound of a noble gas, xenon hexafluoroplatinate . Compounds of other noble gases were discovered soon after: in 1962 for radon, radon difluoride (RnF 2), which was identified by radiotracer techniques and in 1963 for krypton, krypton difluoride (KrF 2). The first stable compound of argon was reported in 2000 when argon fluorohydride (HArF) was formed at a temperature of 40 K (− 233.2 ° C; − 387.7 ° F). </P> <P> In December 1998, scientists at the Joint Institute for Nuclear Research working in Dubna, Russia bombarded plutonium (Pu) with calcium (Ca) to produce a single atom of element 114, flerovium (Fl). Preliminary chemistry experiments have indicated this element may be the first superheavy element to show abnormal noble - gas - like properties, even though it is a member of group 14 on the periodic table . In October 2006, scientists from the Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory successfully created synthetically oganesson (Og), the seventh element in group 18, by bombarding californium (Cf) with calcium (Ca). </P> <Table> <Tr> <Th> Property </Th> <Th> Helium </Th> <Th> Neon </Th> <Th> Argon </Th> <Th> Krypton </Th> <Th> Xenon </Th> <Th> Radon </Th> </Tr> <Tr> <Td> Density (g / dm) </Td> <Td> 0.1786 </Td> <Td> 0.9002 </Td> <Td> 1.7818 </Td> <Td> 3.708 </Td> <Td> 5.851 </Td> <Td> 9.97 </Td> </Tr> <Tr> <Td> Boiling point (K) </Td> <Td> 4.4 </Td> <Td> 27.3 </Td> <Td> 87.4 </Td> <Td> 121.5 </Td> <Td> 166.6 </Td> <Td> 211.5 </Td> </Tr> <Tr> <Td> Melting point (K) </Td> <Td> 0.95 (at 25 bar) </Td> <Td> 24.7 </Td> <Td> 83.6 </Td> <Td> 115.8 </Td> <Td> 161.7 </Td> <Td> 202.2 </Td> </Tr> <Tr> <Td> Enthalpy of vaporization (kJ / mol) </Td> <Td> 0.08 </Td> <Td> 1.74 </Td> <Td> 6.52 </Td> <Td> 9.05 </Td> <Td> 12.65 </Td> <Td> 18.1 </Td> </Tr> <Tr> <Td> Solubility in water at 20 ° C (cm / kg) </Td> <Td> 8.61 </Td> <Td> 10.5 </Td> <Td> 33.6 </Td> <Td> 59.4 </Td> <Td> 108.1 </Td> <Td> 230 </Td> </Tr> <Tr> <Td> Atomic number </Td> <Td> </Td> <Td> 10 </Td> <Td> 18 </Td> <Td> 36 </Td> <Td> 54 </Td> <Td> 86 </Td> </Tr> <Tr> <Td> Atomic radius (calculated) (pm) </Td> <Td> 31 </Td> <Td> 38 </Td> <Td> 71 </Td> <Td> 88 </Td> <Td> 108 </Td> <Td> 120 </Td> </Tr> <Tr> <Td> Ionization energy (kJ / mol) </Td> <Td> 2372 </Td> <Td> 2080 </Td> <Td> 1520 </Td> <Td> 1351 </Td> <Td> 1170 </Td> <Td> 1037 </Td> </Tr> <Tr> <Td> Allen electronegativity </Td> <Td> 4.16 </Td> <Td> 4.79 </Td> <Td> 3.24 </Td> <Td> 2.97 </Td> <Td> 2.58 </Td> <Td> 2.60 </Td> </Tr> </Table> <Tr> <Th> Property </Th> <Th> Helium </Th> <Th> Neon </Th> <Th> Argon </Th> <Th> Krypton </Th> <Th> Xenon </Th> <Th> Radon </Th> </Tr>

The boiling points of the elements helium neon argon krypton