Final answer:
The oxidation number of hydrogen is +1 when combined with nonmetals and -1 when combined with metals. This distinction helps in keeping track of electron movement during chemical reactions. Examples include H2O with hydrogen at +1, and LiH with hydrogen at -1.
Step-by-step explanation:
Oxidation Numbers of Hydrogen
The oxidation number of hydrogen when combined with nonmetals is typically +1. This is because hydrogen usually acts as the reducing agent and is assumed to have lost an electron in such compounds. For instance, in water (H₂O), each hydrogen atom has an oxidation number of +1. In contrast, when hydrogen is combined with metals, it often takes a negative oxidation number of -1. This occurs in binary hydrides, such as lithium hydride (LiH) where hydrogen is treated as if it has gained an electron from the metal. It's crucial to remember that these are conventions used to track electron movement during reactions and do not necessarily represent actual ionic charges in the molecules.
For practice examples, consider hydrogen gas (H₂) where both atoms have an oxidation number of 0. In magnesium chloride (MgCl₂), magnesium has an oxidation number of +2 while chlorine is -1. In hydrogen peroxide (H₂O₂), each hydrogen has an oxidation number of +1 and each oxygen atom is assigned -1.