The Periodic Table
Cambridge O Level Chemistry 5070 — 8.5 Noble Gases — Cambridge O Level Chemistry 5070 Revision Notes & Topical Questions
5 min read 4 parts Lesson 5 of 5
Lesson summary
8.5 Noble Gases — Cambridge O Level Chemistry: describe the position, properties and electron arrangements of the noble gases and explain their low reactivity. The noble gases are the elements in Group 0, also called Group VIII in some older tables.
- Key distinction
- Worked explanation
Section 1 of 4The noble gas group
The noble gas group
The noble gases are the elements in Group 0, also called Group VIII in some older tables. They are non-metals. The group includes helium, neon, argon, krypton and xenon.
At room temperature they are colourless gases with low melting and boiling points. They are monatomic: each particle is one atom rather than a molecule made of two or more atoms. The weak attractions between separate atoms help explain their low boiling points.
Section 2 of 4Electron arrangements
Each noble gas has a full outer electron shell. Helium has the arrangement 2; neon has 2,8; argon has 2,8,8. The larger atoms also have complete outer shells: krypton has 2,8,18,8 and xenon has 2,8,18,18,8.
Key distinction
Helium's first shell is full with two electrons. For the other noble gases listed here, the outer shell is full with eight electrons. Do not state that every noble gas needs eight outer electrons.
Section 3 of 4Why they are unreactive
A full outer shell is a stable electron arrangement. Noble gas atoms have little tendency to gain, lose or share electrons, so they are much less reactive than most other elements. In O Level questions they are commonly described as inert.
Worked explanation
Explain why neon rarely forms compounds
- a neon atom has the electron arrangement 2,8.
- Its outer shell is complete, so it does not readily gain, lose or share electrons to become more stable.
Section 4 of 4Check your understanding
- 1.
- State three physical properties of noble gases.
- 2.
- What does monatomic mean?
- 3.
- Write the electron arrangements of helium, neon and argon.
- 4.
- Explain the low reactivity of argon using its outer shell.
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