Generally, the more empty the outer electron shell, the more reactive the element. Helium has two(2) electrons, and is thus full, all the other noble elements has eight(8) electrons in it's outer electron shell, so they are also full. *And for everyone's sake, krypton is not green, but colorless, and forms white crystals when solid.
(a) Jubilees was written between 153 B.C. and the year of Hyrcanus' breach with the Pharisees. (1) It was written during the pontificate of the Maccabean family, and not earlier than 155 B.C., when this office was assumed by Jonathan the Maccabee.
Jubilee Bible 2000. And it came to pass in the six hundredth and first year of Noah, in the first month, the first day of the month, the waters were dried up from off the earth, and Noah removed the covering of the ark and looked and, behold, the face of the ground was dry.