Lesson focus: Group 0 gases are very unreactive because their outer electron shells are full, while their physical properties still change down the group.
Explain the low reactivity of Group 0 and use property data to select a noble gasA very unreactive gas in Group 0 of the periodic table, such as helium or neon. for a purpose.
Build on earlier learning
The elements of Group 7Group 7 atoms react by gaining one electron to complete their outer shell. Group 0 begins with a full outer shell, providing a useful comparison for reactivity.
You will be successful when you can…
- Describe Group 0 elements as colourless monatomic gases.
- Explain their very low reactivity using full outer electron shells.
- Describe the boiling-point trend down Group 0.
- Select a noble gas for a use by linking several relevant properties.
Words that carry the science
- noble gas
- A very unreactive element in Group 0, also numbered Group 18.
- monatomic
- Existing as individual atoms rather than bonded molecules.
- full outer shell
- An occupied outer electron shell containing its stable maximum number of electrons.
- inert
- Showing little or no chemical reaction under stated conditions.
- boiling point
- The temperature at which a liquid boils at a stated pressure.
- protective atmosphere
- A surrounding gas chosen to prevent unwanted reactions with air.
Connect full outer shells to low reactivity and useful properties
01Noble gases exist as separate atoms
Group 0 elements are colourless gases at room temperature. They are monatomicMade of single atoms that are not joined to each other., meaning that their particles are individual atoms such as He or Ar, not two-atom molecules such as Cl₂.
Helium has two electrons filling its first shell. The other familiar noble gasA very unreactive gas in Group 0 of the periodic table, such as helium or neon. have eight electrons in their outer shell. These stable arrangements mean the atoms do not readily gain, lose or share electrons.
02Very low reactivity makes controlled environments possible
Noble gases are often described as inertDoes not react, or hardly reacts, with other substances., but “very unreactive” is more precise: some heavier noble gases can form compounds under unusual conditions. In everyday and school contexts, their lack of reaction is the important pattern.
Argon can provide a protective atmosphereA gas used around a reactive substance to stop it reacting with the air, like argon around a light bulb filament. in welding and some lamps because it does not readily react with hot metal or a hot filament. Helium is used where a low-density, non-flammable gas is required, such as some balloons.
03Boiling points rise as atoms become larger
boiling pointThe temperature at which a liquid boils, such as 100 °C for pure water. increase down Group 0. Larger atoms have more electrons and stronger temporary attractions between neighbouring atoms, so more energy is needed to separate them into a gas.
The values remain very low, so all the common noble gases are gases at room temperature. A use must match several properties: low density, low reactivity, boiling point, cost and availability can all matter.
Choose a gas for a high-temperature process
A manufacturer needs a gas to surround a hot metal component and reduce unwanted reactions with air. Choose between oxygen and argon.
- Identify the requirement: the surrounding gas should not react readily with the hot component.
- Oxygen supports oxidation and could react with the metal, so it conflicts with the requirement.
- Argon has a full outer electron shell and is very unreactive.
- Conclude using the property that matters rather than merely naming the group.
How to make the reasoning visible: Argon is suitable because its very low reactivity allows it to form a protective atmosphere around the hot metal.
Select a noble gas from evidence
Use the rounded boiling-point data and the contextual notes. A good choice states both a useful property and any relevant limitation.
| Gas | Boiling point / °C | Relative density | Relevant context |
|---|---|---|---|
| Helium | −269 | Very low | Non-flammable; limited resource |
| Neon | −246 | Low | Emits orange-red light in a discharge tube |
| Argon | −186 | Higher than neon | Abundant in air; protective atmosphere |
| Krypton | −153 | Higher than argon | Used in some specialist lamps |
| Xenon | −109 | Highest here | Used in some high-intensity lamps |
Describe the boiling-point trend and predict whether xenon is a gas at 20 °C.
Choose a gas for a lightweight, non-flammable balloon and justify why hydrogen is not the safer choice.
Check your understanding
Answer from memory, then check against the suggested answer.
What does monatomic mean?
Why are noble gases very unreactive?
How does boiling point change down Group 0?
Why is neon useful in a sign but the coloured glow is not evidence that neon gas itself is coloured?
Explain why xenon has a higher boiling point than neon even though both atoms have full outer shells.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Helium is used instead of hydrogen in some balloons.
Explain why helium is so unreactive. Use its group and its electrons.
(3)Explain why a helium balloon rises, and why helium is safer than hydrogen.
(2)Total for this question: 5 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., connect position → electron structure → chemical behaviour, then add the physical property that makes the gas useful.