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K324 / 2027
Periodicity and Metals

Lesson 5 of 8

Recognise noble gases and transition metals

Electron arrangement explains one family; characteristic properties identify another.

O-Level 6092 (2026) / SEC G3 K324 (2027)

  • I can describe noble-gas forms and uses.Syllabus

    Syllabus K324, 8.2(c). Describe noble-gas forms and uses

  • I can explain noble-gas unreactivity.Syllabus

    Syllabus K324, 8.2(d). Explain noble-gas unreactivity

  • I can recognise transition properties.Syllabus

    Syllabus K324, 8.3(a). Recognise transition properties

  • I can recognise catalytic uses.Syllabus

    Syllabus K324, 8.3(b). Recognise catalytic uses

Recognise noble gases and transition metals

Electron arrangement explains one family; characteristic properties identify another.

Group 18 elements have filled outer shells, making them chemically unreactive under ordinary conditions. Helium has two outer electrons; neon and argon have eight. They do not need to gain, lose or share electrons to reach this stable arrangement.

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Noble gases exist as single atoms. Argon supplies an inert atmosphere in filament lamps and in steel manufacture, helping prevent unwanted oxidation. Neon is used in discharge lighting. Helium is useful in balloons because it is low-density and unreactive.

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Typical transition-element properties
PropertyExample or significance
High melting point and densityUseful metal properties; compare with softer, low-density group-1 metals
Variable oxidation statesIron forms Fe2+ and Fe3+ compounds
Coloured compoundsCopper(II) solutions are often blue; iron compounds show different colours
Catalytic activityIron in ammonia synthesis; nickel in hydrogenation; manganese(IV) oxide catalysing hydrogen peroxide decomposition

Check your understanding

Helium has only two electrons. Why is it unreactive?

  1. Its two electrons are shared, so it already has one bond.
  2. Two electrons fill its first shell, so its outer shell is full.
  3. It is too small for other atoms to collide with it often.
Show the answer

Two electrons fill its first shell, so its outer shell is full.

The first shell holds a maximum of two electrons. Like the other noble gases, helium has a full outer shell, so it does not tend to lose, gain or share electrons.

Check your understanding

Neon is 2.8 and argon is 2.8.8. Why do they exist as single atoms and not form compounds?

  1. Their atoms are joined by strong covalent bonds, so they cannot react with anything else.
  2. Their outer shells are nearly empty, so they have no electrons to share with other atoms.
  3. Each atom already has a full outer shell, so it does not lose, gain or share electrons.
Show the answer

Each atom already has a full outer shell, so it does not lose, gain or share electrons.

A full outer shell is a stable arrangement. With no tendency to bond, neon and argon atoms do not join to each other (they are monoatomic) or react to form compounds.

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Check your understanding

Which property is typical of transition elements such as iron and copper, but not of Group 1 metals?

  1. They have low densities and are soft enough to cut with a knife
  2. They conduct electricity well when they are solid
  3. They form positive ions when they react with non-metals
  4. They form coloured compounds and have more than one oxidation state
Show the answer

They form coloured compounds and have more than one oxidation state

Iron forms green Fe2+ and yellow-brown Fe3+ compounds, and copper(II) compounds are often blue. Group 1 compounds are white, and each Group 1 metal forms one ion, with a 1+ charge.