# Group 0 — The Noble Gases
Group 0 (also called Group 8 or Group 18 in some periodic tables) contains the noble gases: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These elements are unique because they are remarkably unreactive — they almost never form compounds. Their stability makes them both fascinating to study and incredibly useful in everyday applications.
1. Why Are Noble Gases Unreactive?
The key to understanding noble gases is their electron configuration. Every noble gas has a full outer electron shell:
| Noble Gas | Atomic Number | Electron Configuration | Outer Electrons |
|---|---|---|---|
| Helium | 2 | 2 | 2 (full 1st shell) |
| Neon | 10 | 2, 8 | 8 (full 2nd shell) |
| Argon | 18 | 2, 8, 8 | 8 (full 3rd shell) |
| Krypton | 36 | 2, 8, 18, 8 | 8 |
| Xenon | 54 | 2, 8, 18, 18, 8 | 8 |
A full outer shell is an extremely stable arrangement. Noble gases:
- Do not need to gain electrons (outer shell already full)
- Do not need to lose electrons (no energy benefit)
- Do not need to share electrons (already stable)
Since chemical reactions involve the transfer or sharing of electrons, noble gases have no tendency to react. They exist as individual atoms (monatomic), not molecules.
2. Physical Properties
General Properties
- Colourless and odourless gases at room temperature
- Monatomic — exist as single atoms (He, Ne, Ar), not diatomic molecules
- Very low melting and boiling points
- Non-flammable
- Poor conductors of electricity under normal conditions (but glow when electricity passes through them at low pressure)
Trends Down the Group
| Property | Trend | Reason |
|---|---|---|
| Boiling point | Increases | Larger atoms → stronger London dispersion forces between atoms |
| Density | Increases | Heavier atoms |
| Atomic radius | Increases | More electron shells |
Boiling Points:
| Noble Gas | Boiling Point (°C) |
|---|---|
| Helium | −269 |
| Neon | −246 |
| Argon | −186 |
| Krypton | −152 |
| Xenon | −108 |
Helium has the lowest boiling point of any element (, just above absolute zero).
3. Uses of Noble Gases
Despite (or because of) their unreactivity, noble gases have many important uses:
| Noble Gas | Uses | Why |
|---|---|---|
| Helium | Balloons; airships; MRI scanners (coolant); deep-sea diving gas | Low density; unreactive; very low boiling point (liquid He for cooling) |
| Neon | Advertising signs (red-orange glow) | Glows brightly when electricity passes through |
| Argon | Filling light bulbs; welding shield gas; double glazing | Unreactive — prevents hot filament from oxidising; good insulator |
| Krypton | Photographic flash; some lasers | Produces bright white light |
| Xenon | Headlights (xenon lamps); anaesthetic | Bright light; non-toxic |
| Radon | (No widespread use) | Radioactive — health hazard in some buildings |
Why Unreactivity Matters
In many applications, the noble gas provides an inert atmosphere — an environment where no chemical reactions occur:
- Light bulbs: Argon prevents the hot tungsten filament from reacting with oxygen (which would make it burn out)
- Welding: Argon shields the hot metal from oxygen and nitrogen in the air, preventing weak, oxidised welds
- Food packaging: Argon is used to fill crisp packets and food containers, preventing food from going stale
4. Helium vs Hydrogen for Balloons
A common exam question compares helium and hydrogen for use in balloons:
| Property | Helium | Hydrogen |
|---|---|---|
| Density | Very low (lighter than air) | Even lower (lightest element) |
| Lifting ability | Good | Slightly better |
| Reactivity | Unreactive | Highly flammable |
| Safety | Safe | Dangerous — explosive with air |
Conclusion: Helium is preferred because it is unreactive and non-flammable, making it safe. Although hydrogen provides slightly more lift, the explosion risk (as in the Hindenburg disaster) makes it unsuitable.
5. Noble Gas Compounds
For most of the 20th century, scientists believed noble gases could never form compounds. In 1962, Neil Bartlett created the first noble gas compound — xenon hexafluoroplatinate.
Since then, several xenon and krypton compounds have been made under extreme conditions, but noble gases remain overwhelmingly unreactive under normal circumstances. For GCSE purposes, noble gases are considered inert (unreactive).
Worked Example: Explaining Unreactivity
Question: Explain why argon is unreactive.
Argon has a full outer electron shell (electron configuration 2, 8, 8). It has no tendency to gain, lose, or share electrons because it already has a stable electron configuration. Therefore, it does not form chemical bonds or take part in chemical reactions.
Worked Example: Explaining Trends
Question: Explain why the boiling point of noble gases increases from helium to xenon.
As you go down Group 0, the atoms get larger with more electrons. This means the London dispersion forces (weak intermolecular forces) between atoms become stronger. More energy is needed to overcome these forces, so the boiling point increases.
Worked Example: Choosing a Noble Gas
Question: Explain why argon is used inside light bulbs instead of air.
The tungsten filament in a light bulb reaches very high temperatures. If air were present, the oxygen would react with the hot tungsten, causing it to oxidise and break. Argon is unreactive (inert), so it prevents this reaction and extends the life of the bulb.
7. Practice Questions
- What feature of their electron configuration makes noble gases unreactive?
- Why do noble gases exist as monatomic gases rather than forming molecules like O₂ or N₂?
- Explain why helium is used in airships rather than hydrogen.
- Describe and explain the trend in boiling points of noble gases.
- Give two uses of argon and explain why its unreactivity is important for each use.
Want to check your answers and get step-by-step solutions?
8. Common Misconceptions
| Misconception | Reality |
|---|---|
| Noble gases have zero electrons | They have electrons — their outer shell is simply full |
| Noble gases never form any compounds | Some compounds exist (e.g. XeF₂) but they are rare and require extreme conditions |
| All noble gases are found in equal amounts in air | Argon makes up ~0.93% of air, but others are present in trace amounts |
| Noble gases glow on their own | They only glow when electricity passes through them at low pressure |
| Helium makes your voice higher because it's lighter | Helium changes the speed of sound in your vocal tract, altering the resonant frequencies |
9. Exam Tips
- Always explain unreactivity in terms of a full outer shell — this is the required scientific explanation
- For "explain" questions about uses, link back to the unreactivity (inert nature) of the gas
- Remember that noble gases are monatomic — write He, not He₂
- Know the trend in boiling points and be able to explain it using intermolecular forces
- Questions often ask you to compare helium with hydrogen for balloons
Frequently Asked Questions
Why is Group 0 called Group 0 and not Group 8?
Traditionally called Group 0 because noble gases were thought to have a valency (combining power) of zero — they don't form bonds. Some modern periodic tables label it Group 18.
How were noble gases discovered if they're unreactive?
In 1894, Lord Rayleigh noticed that nitrogen from air was slightly denser than pure nitrogen made chemically. William Ramsay isolated the extra gas — argon. The other noble gases were discovered by similar methods.
Is helium found in air?
Only in trace amounts (~0.0005%). Most helium is obtained from natural gas deposits underground, where it accumulates from radioactive decay of heavy elements.
Summary
- Noble gases have full outer electron shells, making them unreactive (inert)
- They are monatomic, colourless, odourless gases
- Boiling points increase down the group (stronger London dispersion forces)
- Key uses: helium (balloons, cooling), neon (signs), argon (light bulbs, welding)
- Their unreactivity makes them ideal for providing inert atmospheres