The process of combining the atomic orbitals to produce new orbitals (hybrid orbitals) of varying energies and shapes than the initial orbitals, is called hybridization.
VSEPR theory:-
VSEPR stands for, Valence Shell Electron Pair Repulsion theory.
In 1940, Sidgwick and Powell proposed this theory on the basis of the repulsion interaction of the electron pairs in the valence shell of the atoms.
Basically from this theory we can calculate the number of electrons pairs present in a molecule with the help of this formula :
Here, V= the number of valence electrons present in the central atom, N= total number of monovalent atoms, C= cationic charge, and A= anionic charge.
Hybridisation of Mercury (II) chloride using VSEPR theory:-
In Mercury (II) chloride , there are 2 Chlorine atoms that are linked with 1 Mercury atom.
Electronic configuration of Mercury is, hence it has 2 valence electrons in its outermost shell.
Here Chlorine is the monovalent atom as its valency is 1.
So according to the formula, for calculating electron pair, the values of V= 2 (Mercury has 2 valence electrons), N= 2(as there are 2 Chlorine monovalent atom is present), and C= 0 and A=0 (No cations or anions are present in Mercury (II) chloride, hence charge is 0).
Putting the values in the formula we get the number of electron pair
Here total of 2 electron pairs are present, and both of them are bond pairs
Now since there are 2 electron pairs present, the hybridization will be , so its shape will be linear: