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wise otter.Chemistry
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K223 / K225 / 2027
Periodicity and Metals

Lesson 5 of 8

Recognise noble gases and transition metals

Electron arrangement explains one family; characteristic properties identify another.

SEC G2 Science K223 / K225 (2027)

  • I can explain noble-gas unreactivity.Syllabus

    Syllabus K223 / K225, 7.2(c). Explain noble-gas unreactivity

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 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.