# 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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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.