Topic 4 of 7
Recognise noble gases and transition metals
Electron arrangement explains one family; characteristic properties identify another.
O-Level 6092 (2026) / SEC G3 K324 (2027)
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.
Pure only
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.
Pure only
| Property | Example or significance |
|---|---|
| High melting point and density | Useful metal properties; compare with softer, low-density group-1 metals |
| Variable oxidation states | Iron forms Fe2+ and Fe3+ compounds |
| Coloured compounds | Copper(II) solutions are often blue; iron compounds show different colours |
| Catalytic activity | Iron in ammonia synthesis; nickel in hydrogenation; manganese(IV) oxide catalysing hydrogen peroxide decomposition |
Check your understandingHelium has only two electrons. Why is it still unreactive?Think it through, then reveal the answer
Its first shell is full with two electrons. The relevant idea is a filled outer shell, not a rule that every stable atom must have eight outer electrons.