Why does oxygen have an oxidation number of 2?
The Correct Answer and Explanation is :
Oxygen typically has an oxidation number of -2 in most of its compounds, which can be understood through its electronic structure and bonding behavior. Oxygen, found in Group 16 of the periodic table, has six valence electrons. To achieve a stable electron configuration similar to that of the noble gases, it tends to gain or share two additional electrons, resulting in a full octet.
When oxygen forms compounds, it usually does so by gaining two electrons, leading to an oxidation state of -2. This can be observed in common oxides, such as water (H₂O) and carbon dioxide (CO₂). In these compounds, oxygen atoms accept electrons from more electropositive elements (like hydrogen and carbon), effectively reducing their own oxidation state while oxidizing the other elements.
The -2 oxidation state can be attributed to the strong electronegativity of oxygen, which is the tendency of an atom to attract electrons. Oxygen is the second most electronegative element (after fluorine), meaning it has a strong pull on electrons shared in covalent bonds. For instance, in water, the shared electrons are more attracted to the oxygen atom than to the hydrogen atoms, creating a partial negative charge on the oxygen and reinforcing its -2 oxidation state.
However, it’s important to note that oxygen can exhibit other oxidation states, such as -1 in peroxides (like hydrogen peroxide, H₂O₂) and +2 in certain compounds like OF₂ (oxygen difluoride). In these cases, the bonding context and the presence of more electronegative or electropositive elements alter the typical oxidation behavior of oxygen.
In summary, oxygen has an oxidation number of -2 in most compounds due to its tendency to gain two electrons, driven by its electronegativity and the desire to achieve a stable electron configuration. This characteristic is fundamental to understanding chemical bonding and reactivity involving oxygen in various chemical reactions.