Question

According to Hund's rule, the nitrogen atom has ___ unpaired electrons.

• A. 0
• B. 1
• C. 2
• D. 3

Answer 1

The correct option is D 3

Hund's rule states that:

Every orbital in a sublevel is singly occupied before any orbital is doubly occupied. All of the electrons in singly occupied orbitals have the same spin (to maximize total spin). When assigning electrons to orbitals, an electron first seeks to fill all the orbitals with similar energy (also referred to as degenerate orbitals) before pairing with another electron in a half-filled orbital. Atoms at ground states tend to have as many unpaired electrons as possible.

The electron configuration of the nitrogen (Z = 7) atom:$1s^{2}2s^{2}2p^3$. It has three unpaired electrons.

The $p$ orbitals are half-filled; there are three electrons and three p orbitals. This is because the three electrons in the $2p$ subshell will fill all the empty orbitals first before pairing with electrons in them.