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A lanthanoid has the configuration [Xe] 4f⁷ 6s²…

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A lanthanoid has the configuration $[\text{Xe}]\,4f^7\,6s^2$ . Find its atomic number and its period. Then find the atomic number of the d-block element $[\text{Ar}]\,3d^6\,4s^2$ and its group.

Need a reminder? The key ideaShow

The period is the principal quantum number of the outermost shell. s-block: groups 1 and 2, $ns^{1 \text{ or } 2}$ . p-block: groups 13 to 18, group $= 10$ + outer s and p electrons. d-block: groups 3 to 12, group = d electrons + outer s electrons. f-block: lanthanoids (4f, period 6) and actinoids (5f, period 7).

The worked solution

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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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