For example, the electronic configuration for the element boron can be writen as:

1s2 2s2 2p1

However, it is can be written more accurately by taking the different p-orbitals into account:

enter image description here

The electronic configuration with the different p-orbitals starting from boron ascending in atomic number:

B - 1s2 2s2 2px1

C - 1s2 2s2 2px1 2py1

N - 1s2 2s2 2px1 2py1 2pz2

O - 1s2 2s2 2px2 2py1 2pz2

F - 1s2 2s2 2px2 2py1 2pz2

Each type of 'p-orbital' can hold a maximum of 2 electrons. But the way they are assigned to which orbital is not always systematic e.g. the electrons do no wait till, pX orbital is full to be able to fill the next one (I know this has something to do with energy levels and trends in periodic table).

Can someone tell me how this works and how I can use it to be able to write electronic configurations for p-orbitals. It is much easier just using the summation of px + py + pz = pX; but my teacher sometimes writes it out fully...

  • $\begingroup$ Please explain what exactly you want to know in 'how this works'; do you want to know how the Hund's rule works out or the nomenclature system? $\endgroup$
    – Kartik
    Apr 19, 2019 at 17:34
  • $\begingroup$ Remember also that even the "more accurate" notation you've used is somewhat artificial. Consider, e.g., "C: $1s^2 2s^2 2p_x^1 2p_y^1$. This notation may suggest the two 2p electrons occupy the $2p_x \text{ and } 2p_y$ orbitals, leaving the $2p_z$ orbital empty. But that's not the case; the electrons can't tell the difference among them – they're equivalent orbitals. Instead, the two 2p electrons are evenly distributed across the $2p_x, 2p_y, \text{ and } 2p_z$ orbitals. For this reason carbon, as well as all other isolated atoms, have spherically symmetric electron distributions. $\endgroup$
    – theorist
    Apr 20, 2019 at 0:55
  • $\begingroup$ @theorist; I’m not sure what you mean by “electrons can’t tell the difference among them” - doesn’t that go against Hund’s rule? $\endgroup$
    – aesking
    Apr 20, 2019 at 1:51
  • $\begingroup$ (cont.) that before filling up one orbital that is halfly occupied it first fills orbitals with similar energy; I don’t believe the assignment of e- is purely random ... what I don’t understand is why the p values don’t add up to the total summative p value for Nitrogen, Oxygen and Fluorine. F has 3e-s in its 2p shell, O has 4e-s in its 2p shell etc. $\endgroup$
    – aesking
    Apr 20, 2019 at 2:04
  • $\begingroup$ What we label as $p_x, p_y, \text{ and } p_z$ are arbitrary (e.g., you could switch what you label as $p_y \text{ and } p_z$). In the absence of an external field, they're degenerate. The two 2p electrons in carbon thus occupy a linear combination of those three orbitals. And physically, considering $e^-–e^-$ repulsion, it makes sense that the two electrons would want to spread their density among all three orbitals, rather than being confined to two of them. It's been a while since I've played with the details of Hund's rule, so perhaps someone else could address your Hund's rule question. $\endgroup$
    – theorist
    Apr 20, 2019 at 4:14

1 Answer 1


Electrons don't pair up in orbitals before each is singly occupied by Hund's rule of maximum multiplicity. Writing out px, py, pz fully or using p^n notation (n=no of electrons in a p orbital) is a matter of context and circumstance rather than the standard convention; you might use the 'full version' when explaining bonding through hybridization but omit it while stating the electronic configuration of an atom generally. Both notations are quite interchangeable.

  • $\begingroup$ Hi Kartik, "if it is a matter of preference" then how in exam situations are we expected to discern the element or ion from its e- config using the Cartesian axes of pX, pY & pZ? For example what element has the following e. config: 1s2 2s2 2px1 2py1 2pz2. I would need to know this works and how the e- are assigned to be able to do this..or even write them out myself. $\endgroup$
    – aesking
    Apr 19, 2019 at 17:36
  • $\begingroup$ @aesking It's mainly a matter of context (you can't go without coordinate representations here)! Px, py, pz can be preferably used also in writing the electronic configuration of any atom in general, standalone. $\endgroup$
    – Kartik
    Apr 19, 2019 at 17:38
  • $\begingroup$ @Kartix I see. Sifting through past exam papers we don't get coordinate representations! (Is there no way?). Or can you exemplify it in a specific context so I have a better understanding. Thanks. $\endgroup$
    – aesking
    Apr 19, 2019 at 17:41
  • $\begingroup$ @aesking You've to write orbital diagrams in your answers the way the image shows in the question; exams may or may not give them. I am still not clear on what exactly you want to know: notation or the chemistry of orbitals? Well, ChemSE always discourages an exam-oriented approach. $\endgroup$
    – Kartik
    Apr 19, 2019 at 17:43
  • 1
    $\begingroup$ @aesking Try reading here: chem.libretexts.org/Under_Construction/…; chem.libretexts.org/Bookshelves/…. $\endgroup$
    – Kartik
    Apr 19, 2019 at 17:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.