Noble gas compound Noble gas compound Noble gas compounds are chemical compounds that include an element from the noble gases, group 18 of the periodic table. Although the noble gases are generally unreactive elements, many such compounds have been observed, particularly involving the element xenon. From the standpoint of chemistry, the noble gases may be divided into two groups: the relatively reactive krypton (ionisation energy 14.0 eV), xenon (12.1 eV), and radon (10.7 eV) on one side, and the very unreactive argon (15.8 eV), neon (21.6 eV), and helium (24.6 eV) on the other. Consistent with this classification, Kr, Xe, and Rn form
Atmosphere of Pluto heated, and its big thermal inertia (provided by non-volatile water ice) greatly slowed down its cooling. That is why gases, which now intensively evaporate from northern hemisphere, cannot quickly condense in the southern, and keep accumulating in the atmosphere, increasing its pressure. Around , the southern hemisphere will cool enough to permit intensive condensation of the gases, and they will migrate there from the northern hemisphere, where is polar day. It will last till equinox near aphelion (about 2113). The northern hemisphere will not lose its volatile ices completely, and their evaporation will supply the atmosphere even at the aphelion.