Group 0 — the noble gases
Group 0 (sometimes labelled Group 8) sits on the far right of the periodic table: helium, neon, argon, krypton, xenon and radon. These are the noble gases — famously unreactive and used wherever a non-reactive atmosphere is needed.
Electronic structure — the key
Each noble gas has a full outer shell of electrons:
- He: 2
- Ne: 2,8
- Ar: 2,8,8
- Kr: 2,8,18,8 (transition metal contributions in shell 3)
A full outer shell is the most stable arrangement — they have no need to gain, lose or share electrons. So they don't react under normal conditions and are monatomic (single atoms, not diatomic molecules).
Trends down the group
| Property | Trend down group |
|---|---|
| Boiling point | Increases |
| Density | Increases |
| Atomic radius | Increases |
| Reactivity | Almost zero — but heaviest noble gases (Xe, Kr) can form some compounds with very reactive elements |
Why does boiling point rise down the group? Atoms have more electrons → stronger intermolecular forces (induced dipole forces between atoms) → more energy needed to separate them. Larger atoms = stronger temporary dipoles.
Boiling points to memorise approximately:
- He: −269 °C
- Ne: −246 °C
- Ar: −186 °C
- Kr: −152 °C
Uses
Each gas is used because of its inertness — and sometimes because of its physical properties:
- Helium — balloons and airships (less dense than air, doesn't burn, unlike hydrogen which is risky).
- Helium also used in deep-sea diving mixtures (low density helps breathing under pressure).
- Neon — orange-red glow in advertising signs ("neon lights").
- Argon — fills filament light bulbs (stops the tungsten filament from oxidising and burning); also shielding gas for arc welding.
- Krypton and xenon — special lighting (camera flashes, headlights).
Why are they so unreactive?
Reactivity in chemistry comes from atoms wanting to gain, lose or share electrons. Noble gases already have a stable outer shell, so they don't react under most conditions. This is the gold-standard exam answer to "explain unreactivity".
Discovery
Noble gases were discovered surprisingly late (1894–1898) by William Ramsay, because they are colourless, odourless and don't react. Argon's discovery was the trigger — it had the wrong density to be nitrogen, leading Ramsay to recognise an entirely new family.
⚠Common mistakes
- Saying noble gases are "always inert". Heavier ones (Kr, Xe) can form a few compounds with very electronegative elements.
- Saying boiling point decreases down the group. It increases.
- Forgetting noble gases are monatomic. Don't write He₂ — it's just He.
- Saying they have no electrons. They have full outer shells, not none.
Links
Builds on C1.4 (electronic structure). Comparison with the very reactive C1.7 (Group 1) and C1.8 (Group 7) is a common exam contrast.
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