The elements in Group 0 are called the noble gases. They are unreactive and do not easily form molecules. The reason is that their atoms have stable arrangements of electrons. The noble gases have eight electrons in their outer shell, except for helium, which has only two electrons because its first shell is full.
The boiling points of the noble gases increase with increasing relative atomic mass, which means they increase going down the group. For example, helium boils at -269 °C, neon at -246 °C and argon at -186 °C.
This trend lets us predict properties. Krypton is below argon in Group 0, and xenon is lower still, so the trend can be used to predict whether their boiling points are higher or lower than that of argon.
