How is the oxidation state determined for an atom in a compound?

The oxidation state of an atom in a compound is determined by assigning shared electrons to the atom that has a greater electronegativity, or attraction for electrons. This method of assigning oxidation states is grounded in the concept of electron ownership in covalent bonds. When two atoms share electrons, the atom that is more electronegative will be considered to "own" the shared electrons, which effectively gives it a partial negative charge.

For example, in a molecule like water (H₂O), the oxygen atom is more electronegative than the hydrogen atoms. As a result, we assign the electrons in the O-H bonds to oxygen, leading to an oxidation state of -2 for oxygen (since it is more electronegative) and +1 for each hydrogen.

This method allows for a systematic way of understanding the oxidation state in various compounds, making it easier to predict chemical behavior, reactivity, and the types of reactions that might occur. The determination of oxidation states is crucial in redox reactions, where changes in oxidation states signify the transfer of electrons.