Final answer:
A chemical reaction where a molecule or atom loses electrons is called an oxidation, which is part of a redox reaction where this loss is coupled with a gain of electrons by another substance.
Step-by-step explanation:
A reaction in which a molecule or atom loses electrons is called an oxidation. This process is driven by the electron affinity difference between substances. Just as rocks move downhill due to gravity, electrons move from molecules with lower electron affinity to those with higher affinity, releasing energy in the process. This reaction is energetically favored, much like a rock will naturally roll downhill rather than uphill.
In the context of redox reactions, the substance that loses the electrons, thereby being oxidized, experiences an increase in its oxidation number. Conversely, the substance that gains electrons is said to be reduced, and its oxidation number decreases. Oxidation and reduction always occur simultaneously, defining a redox reaction.
Atoms may lose electrons in order to achieve a more stable electron configuration, which is often the valence electron configuration of the nearest noble gas. This reflects a natural tendency to reach an energetically favorable state.