Which series of quantum numbers describes the highest (energy) occupied orbital in a ground state of At atom?

a) n = 6, l = 0
b) n = 6, l = 2
c) n = 5, l = 2
d) n = 4, l = 3
e) n = 6, l = 1

According to my teacher, the answer is e.

My analysis:

  • The electron configuration of At atom:

$$\begin{aligned}1s^22s^22p^63s^23p^6\ce{3d^10}4s^24p^64\ce{d^10}5s^25p^64\ce{f^14}\ce{5d^10}6s^26p^5 \end{aligned}$$

Knowing for levels 0,1,2,3 correspond to s,p,d,f respectively we can say that:

a) $$\begin{aligned}6s^2\end{aligned}$$ b) $$\begin{aligned}Nothing \end{aligned}$$ c) $$\begin{aligned}\ce{5d^10}\end{aligned}$$ d) $$\begin{aligned}\ce{4f^14}\end{aligned}$$ e) $$\begin{aligned}\ce{6p^5}\end{aligned}$$

What I thought here first is that d is the answer since 4f14 has the largest number of electrons, and thus will occupy the highest energy around.

Then I saw on another question that the orbitals are filled so that the ones of lowest energy are filled first.

$$1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s ...$$

In this case, e is the answer since 6p5 has the highest energy regardless of the number of electrons it is holding?

  • $\begingroup$ Your second way of thinking about it is correct. The number of electrons in the orbital is not the determining factor here. Well written question. $\endgroup$ Commented Oct 8, 2014 at 18:15

1 Answer 1


Yes , there is another name for it (n+l) rule or Aufbau principle


Even though it is not correct to check this rule at such higher values of Z where the trend sometimes changes due to very less differnce between higher values of shell and orbitals .But if you are a beginner you should not heed to this statement.


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