2.12 - Group 0 - The Noble Gases

The noble gases and why they are unreactive

• Group 0 contains the noble gases: helium, neon, argon, krypton, xenon and radon.
• They are all colourless, non-flammable gases at room temperature.

Why they are unreactive

• Every noble gas atom has a full outer shell of electrons (2 for helium, 8 for the others), giving them a stable electron arrangement.
• Because their outer shell is full, they don't need to gain, lose or share electrons.
• This makes them inert (unreactive), so they don't readily form compounds.
• They exist as single, unbonded atoms (monatomic).

The trend in physical properties down Group 0

• The noble gases all have very low melting and boiling points, so they're all gases at room temperature.
• Going down Group 0:
  • Boiling point and melting point increase
  • Density increases
• Boiling points increase down the group because the atoms have more electrons. This increases the attractive forces between atoms, so more energy is needed to pull them apart.

Predicting missing properties

• Because the trend is steady, a missing value can be estimated by taking the average of the elements above and below it.
• To estimate the boiling point of xenon (between krypton and radon):

$$\frac{-153+(-62)}{2}=-107.5\text{ °C}$$

This gives an estimate of about -108 °C (its actual boiling point is -108 °C).