Noble gas stability and unreactivity

The elements in Group 0 are called the noble gases. Their atoms are very stable because their outer electron shells are already full.

For most noble gases, a full outer shell contains eight electrons. Helium is an exception: its only electron shell is the first shell, which is full with two electrons.

Because their outer shells are complete, noble gas atoms do not tend to gain, lose or share electrons. They are therefore very unreactive compared with many other elements.

Noble gas atoms are already stable as single atoms, so they do not readily bond together to form molecules. They are usually found as individual atoms.

Noble gas property trends

A property trend describes how a property changes across the elements in a group. For the noble gases in Group 0, boiling points increase down the group, as relative atomic masses also increase.

The boiling point is the temperature at which a liquid changes to a gas. A noble gas lower down Group 0 has a higher boiling point than one above it.

Predicting noble gas boiling points

The direction of the trend can be used to predict an unknown boiling point. For example, neon lies between helium and argon in Group 0, so its boiling point is expected to lie between theirs. Krypton lies below argon, so its boiling point is expected to be higher than argon’s.

A prediction between known values is generally more certain than one beyond known values, where the pattern may change. The trend does not necessarily increase by equal amounts: do not assume it is linear without supporting data.