hund's rule states that the electrons pair up only after each orbital in a sublevel is occupied by _________________ fill in blank ?

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Payal Khullar | College Teacher | (Level 2) Associate Educator

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Hund's rule states that the electrons pair up only after each orbital in a sublevel is occupied by one electron.

Explanation:

This means that first one electron occupies an orbital in the sublevel and only after that, pairing starts to occur in that orbital. For your understanding, I have given an example to show how pairing of electrons occurs in, say the orbitals of “2p” sublevel.

= electrons 

(Note that upper and down arrow represent electrons with opposite spins (+/-) as no two electrons in an orbital can have the same spin).

2p can accommodate 6 electrons in 3 orbitals. Hence each orbital gets 3 pairs of electrons.


_ ­_ _ (The _ represent the 3 orbitals of 2p)

2p
↑ _ _ (First electron in first orbital) 

2p
↑ ↑ _ (Second electron)


2p
↑ ↑ ↑ (Third electron)


2p
↑↓ ↑ ↑(Pairing of electrons starts in first orbital)


Hence pairing occurs after each of the three orbitals get occupied with one electron.