Question

What is the oxidation number of chlorine atoms in HCl, $C{l}_2$and HClO?

Answer 1

Hint: Oxidation number of any atom represents its capability to gain or lose electrons. Oxidation number is dependent on other atoms in a molecule. Oxidation number for any atom in a molecule can be calculated by the fact that the net charge on a molecule is equal to 0.

Complete answer:
The oxidation number or oxidation state of any atom is the ability of that atom to gain or lose electrons. The oxidation state is the charge on an atom when it is in its ionic form, or when in a molecule. The charge is negative when an atom has the tendency to take electrons, while the charge is positive when an atom has an ability to donate electrons.
As the oxidation state is calculated in the form of ions, so the oxidation state of any neutral molecule is zero. So any molecule without a charge has a 0 oxidation number. Then by adding the respective oxidation numbers we can take out the oxidation number of any element to be positive or negative.
So, finding the oxidation number of chlorine in:
-HCl, this molecule has $H^{+}$ and $C{l}^{-}$, as hydrogen has a +1, then chlorine will have,
+1 + Cl = 0, so Cl = -1. So, chlorine has -1 in HCl.
-$C{l}_2$is a gas in its elementary form. Both the chlorine atoms have equal tendency to gain electrons, so the charge on this diatomic molecule is 0. So, chlorine in $C{l}_2$has 0 oxidation number.
-HClO is hypochlorous acid. The charge on hydrogen is +1, while on oxygen is -2, so chlorine will have,
+1 + Cl + (-2) = 0
Cl = +2 – 1
Cl = +1
So, it has +1 oxidation number.
Hence, the oxidation number of chlorine atoms in HCl, $C{l}_2$and HClO is -1, 0, and +1 respectively.

Note:
Alkali metals have a +1 oxidation state, alkaline earth metals have +2 oxidation state, all halogens have a -1 oxidation state, while oxygen in oxide has -2, in peroxide has -1 and in superoxide has -2. Chlorine has positive oxidation number in HClO as oxygen is more electronegative than chlorine due to the small size of oxygen.