An electron in a hydrogen atom can indeed exist in an energy eigenstate, particularly when the atom is isolated from external interactions. In such a scenario, measuring the electron's energy will confirm that it occupies a specific energy level, thus qualifying as an energy eigenstate. However, in practical situations, hydrogen atoms often interact with one another, forming diatomic molecules, which alters their energy states. The covalent bond in these diatomic hydrogen molecules is relatively weak, allowing for reactivity under certain conditions. Therefore, while an isolated hydrogen atom's electron can be in an energy eigenstate, this is less common in molecular contexts.