Question

How do you calculate formal charge of a molecule?

Answer 1

The formal charge is the (valence electrons - (nonbonding electrons $+\frac{1}{2}$ bonding electrons)).
For example:

$N{H}_3$ has one lone pair and three bonds with hydrogen. It is in the group $5A,$ so it has $5$ valence electrons.

Thus, $5-(2+(1/2\left)\right(6)=0$

So, $N{H}_3$ has a formal charge of $0.$

$N{H}_4$ has no lone pairs and four bonds with hydrogen.

Thus, $5-(0+(1/2\left)\right(8\left)\right)=1$

So, $N{H}_4$ has a $+1$ formal charge.