Question

How does formal charge relate to the number of valence electrons?

Answer 1

Hint : We know that formal charge is the number of electrons around a neutral atom vs the number of electrons present around the atom in molecules. It is assumed that when a chemical bond is shared, the bonds are equally shared between the atoms and thus the formal charge is assigned.

Complete Step By Step Answer:
The formal charge of each atom in a molecule can be calculated using the following equation: Formal charge $ = $ no. of valence electrons in free atom $ - $ no. of lone pair electrons $ -\dfrac{1}{2} $ no. of bond pair electrons.
When we talk about oxidation or reduction reactions, we are conceived that they occur in an atom’s valence shell. The formal charge is thus related to the presence or absence of the valence electrons present in the outermost shell. There isn’t any relative electronegativity taken into consideration.
For example, we know oxygen has an atomic number of eight. This means that an oxygen atom will have eight protons in its nucleus and eight electrons in its orbit, with two of these inner core electrons and six present in the outermost shell. Thus, we can see that in an oxygen molecule $ R-O-R $ is the presentation of its depiction with two lone pairs on oxygen.
When we see the two lone pairs, it is known that they have a charge which is associated with the oxygen atom entirely while the oxygen centre is conceived to comprise half a share of the two electrons which are present in a $ C-O $ bond with one electron. Thus for the formal charge, an oxygen atom has eight protons in its nucleus.

Note :
Remember that in order to calculate the formal charge; we assign electrons in the molecules to individual atoms as per certain rules. These consist of how non-bonding electrons are assigned to atoms on which they are located and also how bonding electrons are divided equally between two bonded atoms so one electron from each bond goes to each atom.