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.
Next we have the LXX of the Pentateuch, to which we may assign the date 200 B.C.; next the Book of Jubilees just before the Christian era; the Syriac Pentateuch before A.D. 100; the Vulgate of the fourth century; the Targums of Onkelos and Ps.-Jon. in their present form A.D. 300-600.