Atoms in their ground state are considered stable in the sense that they do not spontaneously undergo changes or decay without external influences. The ground state of an atom corresponds to the lowest energy configuration of its electrons, where they occupy the lowest available energy levels.
In quantum mechanics, the ground state is often associated with the most stable arrangement of electrons, and it represents the state of minimum energy for the atom. However, it's important to note that even in the ground state, atoms can still undergo various interactions and processes.
While atoms in the ground state do not typically decay on their own, they can be influenced or perturbed by external factors. External energy, such as absorption of photons or collisions with other particles, can excite atoms and cause transitions to higher energy levels or even ionization (loss or gain of electrons). These processes can lead to changes in the atom's stability and behavior.
Additionally, quantum fluctuations and effects, such as tunneling, can occur even in the ground state. These phenomena can lead to temporary and small fluctuations in the atom's behavior, but they do not typically result in permanent changes or instability.
In summary, atoms in their ground state are considered stable and do not spontaneously decay or change without external influences. However, interactions with the environment or external energy sources can perturb the atom and lead to excitations or other processes that may affect its stability.