Question

Write electronic configurations of the elements (number in the bracket indicate atomic number) Oxygen$\left( 8 \right)$

Answer 1

Hint- To write electronic configuration of oxygen, use Aufbau’s principle which tells the manner in which electrons are filled in atomic orbitals of an atom in ground state. The maximum number of electrons that can be filled in s-orbital is $2$, p-orbital is $6$,d-orbital is $10$ and f-orbital is $14$.

Step-by-Step Solution: We have to write electronic configuration of Oxygen whose atomic number is $8$
According to Aufbau principle,
The electrons first occupy the orbitals whose energy is lowest. The electrons enter higher energy orbitals only when lower energy orbitals are completely filled.
The order of increase in energy of orbitals is determined by (n+l) rule where n is principal quantum number and l is azimuthal quantum number.
If two orbitals have equal (n+l) value then electrons will first enter the orbital having lower n value.
The order of filling of electrons in orbitals is-$1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p$ and so on.
Then using this principle, two electrons will first enter $1s$ orbital. Now two electrons will enter in $2s$ orbital. The remaining four orbitals enter in $2p$ orbital. Hence we can write-

Answer-Electronic configuration of oxygen=$1{s^2},2{s^2},2{p^4}$

Note: There are some exceptions of Aufbau Principle like chromium and copper.
Chromium has atomic number $24$ and has electronic configuration $\left[ {{\text{Ar}}} \right]3{d^5}4{s^1}$ because the orbitals are half-filled and the element is most stable in this configuration. Copper has atomic number $29$ and has electronic configuration $\left[ {{\text{Ar}}} \right]3{d^{10}}4{s^1}$ because the d-orbital is fulfilled and s-orbital is half-filled and the element is most stable in this configuration.