What is the octet rule and how is it used in covalent bonding?

The octet rule is the fundamental explanation to give the reasons as for why atoms would undergo complex molecular and ionic arrangements, by sharing or transferring valence or bonding electrons between atoms in a compound.

It states that atoms would need to have the maximum number of electrons in their valence shell to be inactive and stable. Thus atoms would tend to bond to other atoms to achieve this Lower energy and stability.

They do this by sharing between electrons between atoms as in covalent bonds.

2.00 is the !

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.