The elements in Group 0 are called the noble gases: helium, neon, argon, krypton, xenon and radon. They are unreactive and do not easily form molecules. The reason is the arrangement of electrons in their atoms. Helium has two electrons in its outer shell, which is full for the first shell. The other noble gases have eight electrons in their outer shell, which is also full. A full outer shell is a stable arrangement, so these atoms have no need to lose, gain or share electrons.
The boiling points of the noble gases increase going down the group, as the relative atomic mass increases. Helium boils at -269 °C, neon at -246 °C, argon at -186 °C and krypton at -153 °C. This trend lets you predict a property: xenon is further down the group than krypton, so its boiling point must be higher than -153 °C. In the same way, radon has a higher boiling point than xenon.
