Cambridge O Level Chemistry · Syllabus 5070 · The Periodic Table
Noble Gas
What is Noble Gas?
An element of Group VIII, the last column of the Periodic Table. Noble gases are unreactive gases that exist as single, unbonded atoms rather than as molecules. Their unreactivity follows from having a full outer electron shell, so there is no tendency to lose, gain or share electrons.
This definition is part of the The Periodic Table chapter in Cambridge O Level Chemistry.
Noble Gas in context
Down Group I the alkali metals become more reactive and lower-melting as the single outer electron is lost more easily, while down Group VII the halogens become less reactive as it becomes harder to gain the extra electron needed to fill the outer shell. A more reactive halogen displaces the halide ion of a less reactive one from solution. Transition elements, between Groups II and III, show variable oxidation numbers rather than one fixed charge, and Group VIII noble gases are unreactive because their outer shell is already full.
Common mistakes with Noble Gas
- 9 · “Noble gases are unreactive because they have no electrons” Defect Confusing a full outer shell with an empty one, or writing \(\mathrm{Ar_2}\) by analogy with \(\mathrm{Cl_2}\). Fix Argon has \(18\) electrons, arranged \(2,8,8\). It is unreactive because the outer shell is full, so there is no advantage in losing, gaining or sharing. A full shell also means no bonding to another argon atom: noble gases are monatomic, written \(\mathrm{He}\), \(\mathrm{Ne}\), \(\mathrm{Ar}\).
- Error 6 · “Group VIII elements form ions with a charge of \(8+\).” Defect The pattern continued into a group where it does not apply. Chemistry Ions form in order to reach a full outer shell. A noble gas already has one, so there is no reason to lose or gain anything. Group VIII normally forms no ions at all. Repair Group VIII: no ion. Write it as an atom — \(\mathrm{Ar}\), \(\mathrm{Ne}\). Transfer What ion does neon form? None.
- Error 18 · “Noble gases are unreactive because they have no electrons — and argon is \(\mathrm{Ar_2}\).” Defect Two errors: a full shell mistaken for an empty one, and a diatomic formula for a monatomic element. Chemistry Argon has \(18\) electrons, arranged \(2,8,8\). Its outer shell is full, which is why there is no tendency to lose, gain or share — and why it does not bond even to another argon atom. Repair “Full outer shell”, and write \(\mathrm{Ar}\), never \(\mathrm{Ar_2}\). Transfer How many electrons does argon have altogether, and how many in its outer shell? \(18\) altogether, \(8\) in the outer shell.
Questions students ask about Noble Gas
Why are the noble gases unreactive?
Noble gases already have a full outer electron shell, so there is nothing to gain by losing, gaining or sharing electrons. This is also why they exist as single, unbonded atoms rather than forming molecules, and why Group VIII elements normally form no ions at all.