Ground state: definition in chemistry
Ground state: The lowest-energy arrangement of the electrons in an atom, ion or molecule.
In the ground state, electrons occupy the available orbitals in order of increasing energy, following the aufbau principle, the Pauli exclusion principle and Hund's rule. When an atom absorbs energy, an electron can jump to a higher orbital, giving an excited state. When it falls back to the ground state it releases the extra energy, often as light of a specific frequency.
Examples
- Hydrogen: 1s¹
- Carbon: 1s² 2s² 2p²
- Sodium: [Ne] 3s¹
- Chromium is an exception: [Ar] 3d⁵ 4s¹, not [Ar] 3d⁴ 4s²
On the periodic table
Electron configurations given for elements are ground-state configurations, and an element's position shows how they end: for example, every group 1 element ends in s¹.