Here are some common scenarios and exceptions regarding the oxidation number of oxygen:
1. In Oxides: In binary compounds formed between oxygen and a metal, such as metal oxides, the oxidation number of oxygen is usually -2. For example, in magnesium oxide (MgO), the oxidation number of oxygen is -2, while magnesium has an oxidation number of +2.
2. Peroxides and Superoxides: In peroxides, such as hydrogen peroxide (H2O2), the oxidation number of oxygen is -1. This is because the oxygen-oxygen bond in peroxides contains a single bond and a single electron pair shared between the two oxygen atoms. In superoxides, like potassium superoxide (KO2), the oxidation number of oxygen is -1/2. This is due to the presence of an unpaired electron in the oxygen-oxygen bond.
3. Oxygen Fluorides: In oxygen fluorides, such as oxygen difluoride (OF2), the oxidation number of oxygen is +2. This is because fluorine is more electronegative than oxygen, causing oxygen to lose two electrons and acquire a positive oxidation number.
4. Compounds with Hydrogen: In compounds where oxygen is bonded to hydrogen, such as water (H2O), the oxidation number of oxygen is usually -2. This is because the electronegativity of oxygen is higher than hydrogen, resulting in a partial negative charge on oxygen and a partial positive charge on hydrogen.
5. Organic Compounds: In organic compounds, the oxidation number of oxygen can vary depending on the specific functional group. For example, in alcohols, the oxidation number of oxygen is -1, in ethers, it is -2, and in carboxylic acids, it is -1.
It's important to note that the oxidation number assigned to an atom is a formal concept used to represent the electron transfer within a molecule. In reality, the electron distribution in molecules is more complex and may involve partial charges rather than discrete integer values.
