定义Definition
基态是原子、分子或离子能量最低的状态。基态原子的电子按构造原理、泡利不相容原理和洪特规则排布在能量最低的轨道上。吸收能量后电子跃迁到较高能级，称为激发态。
The ground state is the lowest-energy state of an atom, molecule or ion. In a ground-state atom the electrons occupy the lowest available orbitals according to the Aufbau principle, the Pauli exclusion principle and Hund's rule. Absorbing energy promotes an electron to a higher level, giving an excited state.
激发与发射Excitation and emission
激发态不稳定，电子回到较低能级时以光的形式放出能量，光的频率由 ΔE = hν 决定。原子发射光谱由一系列分立的谱线组成，说明电子能量是量子化的；焰色反应也是这一原理。
Excited states are unstable; when an electron falls to a lower level it emits light of frequency given by ΔE = hν. Atomic emission spectra consist of separate lines, showing that electron energies are quantised; flame tests work the same way.
书写示例Examples
基态 C：1s² 2s² 2p²，两个 2p 电子分占两个轨道、自旋平行；基态 Fe：[Ar] 3d⁶ 4s²；激发态碳的一种排布为 1s² 2s¹ 2p³。
Ground-state C: 1s² 2s² 2p², the two 2p electrons in separate orbitals with parallel spins; ground-state Fe: [Ar] 3d⁶ 4s²; one excited configuration of carbon is 1s² 2s¹ 2p³.