EasyChemistryHigh School (9–10)GeneralStructure of the Atom › Electronic Configuration and ValencyConceptual

Which of these atoms have a full outer shell?

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

Helium ( $2$ ), fluorine ( $2, 7$ ), neon ( $2, 8$ ), sodium ( $2, 8, 1$ ), argon ( $2, 8, 8$ ).

What is special about the atoms that do?

Need a reminder? The key ideaShow

The valence electrons are those in the outermost shell. With $1$ to $4$ of them, the valency is that number; with $5$ to $7$ , it is $8$ minus the number. A full outer shell gives a valency of $0$ . Atoms lose, gain or share electrons to reach a full outer shell, like a noble gas.

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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← Find the valency of lithium (2, 1), fluorine (2, 7), phosphorus (2, 8, 5) and argon (2, 8, 8).The calcium ion, Ca²⁺, and the chloride ion, Cl⁻, each have the same electron arrangement as a… →

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