Question

Water is an oxide of hydrogen represented by the formula ${{H}_{2}}O$.However ,the oxide of fluorine is represented by the formula $O{{F}_{2}}$ and not ${{F}_{2}}O$.How do you justify this?

Answer 1

Oxides generally have an oxidation state of −2. In the case of oxygen difluoride, the oxidation state of oxygen is +2. When we are writing the formula of compounds electronegativity also plays a major role.

Complete step by step solution:
- Let's start with the concept of oxides. They are the chemical compounds with one or more oxygen atoms combined with another element. For example, in a water molecule (${{H}_{2}}O$) one oxygen atom is combined with two hydrogen atoms and thus its an oxide of hydrogen.
- Generally, in an oxide oxygen has the oxidation number −2. Thus, it exists as ${{O}^{-2}}$.The oxidation state of oxygen will vary accordingly in peroxides, super oxides etc.
- As we know, oxygen is one of the most electronegative atoms. This means that the oxygen will pull electrons towards itself. When oxygen combines with a metal to form a compound, oxygen pulls electrons from the metal and thus oxide ion is formed.
- This is what happens in the case of water molecules and other examples. Hence, we can say that water is an oxide of hydrogen.
- As we are aware, the fluorine atom is more electronegative than oxygen. As a result, when oxygen combines with fluorine, the electrons of oxygen are getting pulled by fluorine.
- Therefore, in $O{{F}_{2}}$ fluorine is present as fluoride (${{F}^{-1}}$) ion and hence oxygen exists as dipositive ion (${{O}^{+2}}$). So, as we mentioned above an oxide is having an oxidation number of −2. But in $O{{F}_{2}}$ oxygen is having +2 charge. Hence it is not an oxide.
- Thus $O{{F}_{2}}$ is not an oxide of fluorine. Instead, we can say that it is a fluoride of oxygen.

Therefore $O{{F}_{2}}$ is called oxygen difluoride.

Note: The explanation can also be given in a simpler way. When we usually write the symbols or names of compounds, the name of electropositive element is written first and then the name of electronegative element is written. In $O{{F}_{2}}$ oxygen is more electropositive when compared to fluorine. So, oxygen should be written first as in $O{{F}_{2}}$ not as in ${{F}_{2}}O$.