Question

Why is neon monatomic but chlorine is diatomic?

Why is neon monatomic but chlorine is diatomic?

Answers

It has to do with stable shells.

Neon has an atomic number of 10. It has it's first two shells filled 2 and 8 and hence is stable. It is called a Noble gas and doesn't want to share or give/take electrons. For this reason it stays alone - monoatomic.

Chlorine has an atomic number of 17. It has its first two shells filed and 7 of 8 electrons in the third: 2 8 7. It wants to get or share one more electron. Chlorine therefore forms a diatomic molecule so that each Chlorine atom can share one electron with the other, in effect creating stable outer shells.

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