Question

How to compare the formal charge and oxidation number of the chlorine atom in the chlorate ion ?      #   # 

Answer 1

The formal charge on Cl is zero. The oxidation number of Cl is +5.

The definitive way to determine formal charge and oxidation number is to draw the Lewis structure.

Formal Charge

The rules are:

• The lone pair electrons belong entirely to the central atom
• The bonding electrons are shared equally between the bonded atoms.

Here, Cl keeps its two lone pair electrons and gets half (five) of the ten bonding electrons.

That gives it seven valence electrons.

An isolated Cl atom has seven valence electrons, so Cl has neither lost nor gained electrons.

The formal charge of Cl is zero.

Oxidation Number

The rules are:

• The lone pair electrons belong entirely to the central atom
• The bonding electrons belong entirely to the more electronegative atom.

Here, Cl "loses" all the bonding electrons to the more electronegative O atom.

It "owns" only the two lone pair electrons.

An isolated Cl atom has seven valence electrons, so Cl has "lost" 5 electrons

The oxidation number of Cl is +5.