The shape of the lesson
By the end of the lesson, learners can
- Why so unreactive?: Other elements react in order to reach a full outer shell.
- Uses of noble gases: Each use depends on the gas being unreactive, together with one other property.
- Monatomic and unreactive.
- Full outer shells: He 2, Ne 2,8, Ar 2,8,8.
- Down the group: boiling point and density increase.
- Uses depend on unreactivity plus one other property.
One picture every idea returns to
The noble gases in Group VIII are unreactive, monatomic gases. Their atoms have full outer shells (helium 2, neon 2,8, argon 2,8,8), so they do not need to gain, lose or share electrons to become stable. Because they are unreactive they are used where a non-reactive gas is needed: argon in lamps and as an inert atmosphere, helium in balloons and airships, neon in advertising signs.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Content with a full shell.. Helium, neon and argon hardly react with anything. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Why so unreactive? | Other elements react in order to reach a full outer shell. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Uses of noble gases | Each use depends on the gas being unreactive, together with one other property. | Jot Thoughts |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 12 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Uses of noble gases, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Jot Thoughts
Teams write ideas on slips, one idea per slip, as many as they can in two minutes, saying each aloud as they place it in the middle. Then they sort the slips, which is where the structure of the topic appears.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Helium replaced hydrogen in airships because it is unreactive (it does not burn), not just because it is light: hydrogen is even less dense but is flammable. | And helium has 2 outer electrons, not 8, yet its outer shell is still full. |
Noble gases: worksheet
6 questions, 12 marks. Written in the style of the papers; no past paper question is reproduced.
Explain, in terms of electrons, why the noble gases are unreactive.
Give the electronic configurations of helium, neon and argon.
State one use of helium and explain it in terms of its properties.
Suggest why argon, rather than air, is used inside filament light bulbs.
Name the noble gas that has the same electronic configuration as (a) a calcium ion, Ca2+, and (b) an oxide ion, O2−.
Explain the meaning of the term monatomic.
Answer key and marking notes
- Their atoms have full outer electron shells.
- So they do not need to lose, gain or share electrons to become stable.
- Helium: 2.
- Neon: 2,8.
- Argon: 2,8,8.
- Filling balloons or airships.
- It is much less dense than air and unreactive, so it does not burn.
- The filament is very hot and would react with the oxygen in air (burn out).
- Argon is unreactive, so the filament lasts much longer.
- (a) argon (Ca2+ is 2,8,8).
- (b) neon (O2− is 2,8).
Existing as single, separate atoms rather than as molecules.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which description applies to all the noble gases at room temperature?
- Acolourless, monatomic gases
- Bcoloured, diatomic gases
- Ccolourless, diatomic gases
- Dcolourless, monatomic liquids
The diagram shows an outline of part of the Periodic Table with five elements labelled A to E. Which labelled element is an unreactive gas made of single atoms?
- AD
- BE
- CB
- DA
The boiling points of helium, neon and argon are −269 °C, −246 °C and −186 °C. Krypton is the next noble gas below argon. What is the most likely boiling point of krypton?
- A−153 °C
- B−210 °C
- C−255 °C
- D+25 °C
Neon is used in advertising signs. Which property of neon is this use based on?
- AIt glows brightly when electricity passes through it.
- BIt is much less dense than air.
- CIt burns with a bright red flame.
- DIt reacts with the glass to form a coloured coating.
Helium is in Group VIII but has only two electrons in its outer shell. Why is helium unreactive?
- AIts only shell is full with two electrons.
- BIt actually has eight electrons in its outer shell.
- CIt has no electrons to take part in reactions.
- DIts two electrons are shared with another helium atom.
Argon is unreactive and non-flammable, yet it is not used to fill party balloons that float. Why not?
- AArgon is denser than air.
- BArgon is flammable in air.
- CArgon reacts with the rubber of the balloon.
- DArgon is made of diatomic molecules.
An atom of element X gains electrons to form the ion X2−, which has the same electronic configuration as argon. In which group is X?
- AGroup VI
- BGroup II
- CGroup VIII
- DGroup IV
Which pair of ions both have the same electronic configuration as neon?
- AMg2+ and F−
- BMg2+ and Cl−
- CK+ and O2−
- DCa2+ and S2−
Quiz key
The noble gases are all colourless gases made of single, separate atoms (He, Ne, Ar), so they are monatomic. Diatomic molecules such as Cl2 and O2 are formed by elements that need to share electrons; noble gas atoms already have full outer shells and do not bond to each other. None of them is a liquid at room temperature.
D is in Group VIII, the noble gases, whose atoms have full outer shells and exist as single atoms. E is a halogen in Group VII: it is reactive and forms diatomic molecules. B is in Group VI, a reactive non-metal, and A is in Group I, a reactive metal.
Boiling points increase down Group VIII, so krypton boils above argon's −186 °C; its actual boiling point is about −153 °C. Values of −210 °C and −255 °C would mean the trend had reversed. A boiling point of +25 °C is far too high: krypton would then be a liquid at a typical room temperature, but all the noble gases are gases.
Neon gives out a bright glow when an electric current passes through it, and because it is unreactive it lasts a long time inside the tube. Low density is the reason helium is used in balloons. Neon is unreactive, so it does not burn and does not react with the glass.
The first shell can hold only two electrons, so helium's single shell is already full and it has no tendency to gain, lose or share electrons. Helium has two electrons, not eight and not zero. Sharing electrons with another helium atom would make He2 molecules, but helium is monatomic.
To float, a balloon must be filled with a gas that is less dense than air, like helium. Argon is denser than air, so an argon balloon would sink. Argon is unreactive, so it neither burns nor reacts with rubber, and like all noble gases it is monatomic, not diatomic.
X2− has the configuration 2,8,8, so the X atom had two fewer electrons: 2,8,6. Six outer electrons means Group VI (X is sulfur), and Group VI elements gain two electrons to form 2− ions. A Group II element forms 2+ ions by losing electrons (Ca2+ is also 2,8,8, but its charge is positive). Group VIII elements do not form ions, and Group IV elements do not usually form 2− ions.
Magnesium (2,8,2, Group II) loses two electrons to become 2,8, and fluorine (2,7, Group VII) gains one to become 2,8: both match neon. Cl− and K+ are 2,8,8, like argon, so the pairs containing them are wrong even though Mg2+ and O2− are 2,8. Ca2+ and S2− are both 2,8,8, like argon.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.