Question

What is the oxidation number of $Cl$ in $Ba{\left( {Cl{O_2}} \right)_2}$ $?$

Answer 1

First find the sum of the lone pairs of each atom. The oxidation number of each atom can be calculated by subtracting the sum of lone pairs and electrons it gains from bonds from the number of valence electrons. Bonds between atoms of the same element are always divided equally.

Complete answer:
Oxidation number in the number that is allocated to elements in a chemical combination. The oxidation number is basically the count of electrons that atoms in a molecule can share, lose or gain while forming chemical bonds with other atoms of a different element. The oxidation state defines the degree of oxidation of an atom in a molecule, whereas the oxidation number is defined as the charge that the central metal atom will retain even after all the ligands have been removed from the atom.
The oxidation number of $H$ is $+ 1$, but it is $- 1$ when combined with less electronegative elements. The oxidation number of $O$ in compounds is usually $- 2$, but it is $- 1$ in peroxides. The oxidation number of a Group $1$ element in a compound is $+ 1$.
Rules for assigning oxidation numbers are the convention is that the cation is written first in a formula, followed by the anion. The oxidation number of a free element is always 0. The oxidation number of a monatomic ion equals the charge of the ion.
Given $Cl{O_2}^ -$; by the definition the individual oxidation numbers of the elements $\left( {2 \times O + Cl} \right)$ must sum to the charge on the chlorite ion, which is $- 1$. Oxygen gets the charge when we break the $Cl - O$ bonds, so it is $- 2$ (oxygen is more electronegative than $Cl$). So $- 2 + 2 +$(oxidation number of $Cl$)$= - 1$. This gives $Cl$ in chlorite a formal oxidation number of $+ 3$. What is the oxidation number of Cl in perchlorate anion, ClO−4? Please post your answer here.
Note that the oxidation number of $O$ in its compounds is normally $- 2$, as here. Elemental oxygen is $O$, but peroxide $O_2^{ - 2}$ is −I
The oxidation state of $Cl$ in $Ba{\left( {Cl{O_2}} \right)_2}$ is $+ 3$.

Note:
Note that a lone pair means a pair of valence electrons that are not shared with another atom in a covalent bond. Lone pairs are sometimes called an unshared pair or non-bonding pair. Lone pairs are found in the outermost electron shell of atoms.