Ground State
Definition and meaning of Ground State in chemistry.
Ground state is the lowest-energy, most stable configuration of an atom, ion, or molecule, in which its electrons occupy the lowest available energy orbitals allowed by the Pauli exclusion principle.
In more detail
Electrons fill orbitals from lowest to highest energy following the Aufbau principle, with no more than two electrons per orbital (Pauli exclusion) and single occupancy of degenerate orbitals before pairing (Hund's rule). Any configuration with an electron in a higher orbital while a lower one remains empty is an excited state, which is less stable and typically short-lived. Atoms return to the ground state by releasing the absorbed energy, often as a photon, which is the basis of atomic emission spectra used in analytical techniques like flame tests and atomic absorption spectroscopy.
Key facts
| Governing Rules | Aufbau principle, Pauli exclusion principle, Hund's rule |
|---|---|
| Opposite State | Excited state |
| Return Mechanism | Photon emission (relaxation from excited state) |
| Field | General Chemistry |
The ground-state electron configuration of carbon is 1s² 2s² 2p², with its two 2p electrons occupying separate p orbitals with parallel spins per Hund's rule, rather than pairing in one orbital.
Frequently asked questions
What is the difference between ground state and excited state?
The ground state is an atom's lowest possible energy configuration; an excited state has at least one electron promoted to a higher-energy orbital after absorbing energy, such as a photon.
Does every atom have only one ground-state configuration?
Yes, each element has one lowest-energy configuration, though a few elements (like chromium and copper) have configurations that deviate from simple Aufbau predictions due to extra stability from half-filled or filled d subshells.