explain lone pair and formal charges with example in simple language.

The pair of valence electrons which does not take part in active bonding in a molecules are known as lone pair electrons. 

  

 

Formal charge is the difference between the number of valence electrons of each atom and the number of electrons the atom is associated with. Formal charge assumes any shared electrons are equally shared between the two bonded atoms.

 

Formal Charge = [No. of valence electrons on atom] – no of [non-bonded electrons + number of bonds].

 

Let’s apply it to some examples. for example BH4 (top left corner).

• The number of valence electrons for boron is 3.
• The number of non-bonded electrons is zero.
• The number of bonds around boron is 4.

So formal charge = 3 – (0 + 4)  = 3 – 4  = –1