Question

How many unpaired electrons are in an O atom?

Answer 1

Hint: Each bonding or nonbonding electron pair has two electrons which are in opposite spin orientation, $$+1/2$$ and $$-1/2$$ in one orbital based on Pauli's exclusion principle, whereas an unpaired electron is a single electron, alone in one orbital. The oxygen atom contains eight electrons and the configuration of oxygen is$$1s-2,2s-2,2p-4$$. For the determination of unpaired electrons of any atom you should know the number of electrons and electronic configuration of that atom.

Complete step by step answer:
An atom of an element has different shells, subshells and orbitals and the distribution of electrons in these shells is called the electronic configuration.
To calculate unpaired electrons of elements you should know the electronic configuration of that element and the orbital diagrams.
Oxygen is an element that belongs to group $16.$and has a total $8$ number of electrons.
So if we write the electronic configuration of oxygen it will be $1s^2,2s^2,2p^4$
Then we will make the orbital diagrams for oxygen to get the unpaired electrons.

$S$ shell can held maximum of $2$ electrons $p$ shell can hold $6$ electrons.
In writing orbital diagrams:
Lower energy levels are filled first.
When you proceed to produce $p$ subshell you Need to remember Hund's rule-which states that every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied and all electrons in singly occupied orbitals have the same spain.
So from the orbital diagram of oxygen atom we can conclude that oxygen atom we can conclude that oxygen atom contains $2$ unpaired electrons in orbit.

Note: In writing the orbital Diagrams and electron configuration of atoms remember aufbau principle and Hund’s rule.
The aufbau principle states that : According to the Aufbau principle, the available atomic orbitals with the lowest energy levels are occupied before those with higher energy levels.
Hund's rule states that : 1. In a sublevel, each orbital is singly occupied before it is doubly occupied.
2. The electrons present in singly occupied orbitals possess identical spin.