Final answer:
When a compound loses an electron in a chemical reaction, it has been oxidized. This process is part of a redox reaction, where the substance losing electrons increases its positive charge.
Step-by-step explanation:
In a chemical reaction, when a compound loses an electron, the compound has been oxidized. Oxidation is defined broadly today as the loss of one or more electrons by a substance. When a substance loses electrons, its charge will increase because electrons are negative. If an atom loses electrons, it is losing negative charges, resulting in the atom having a greater positive charge. This change in charge signifies that oxidation has occurred.
To illustrate further, in a redox (reduction-oxidation) reaction, one element loses electrons and is oxidized, which increases its oxidation number. Conversely, the element that gains electrons is said to be reduced, and its oxidation number decreases. The concept of oxidation and reduction can also be likened to the movement of rocks downhill due to gravity, as elements move electrons from a lower to a higher affinity, similar to rocks moving to a lower position due to gravity.