Skip to notes
wise otter.Chemistry
Contents
Periodicity and Metals

Topic 4 of 7

Recognise noble gases and transition metals

Electron arrangement explains one family; characteristic properties identify another.

O-Level 5086 / 5088 (2026) / SEC G3 K326 / K328 (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.

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.