- Ground state → The atom’s electrons are in the lowest energy levels. This is the most stable state.
- Excited state → When an atom absorbs energy, an electron jumps to a higher energy level. This state is unstable and short-lived.
Example: In hydrogen
- Ground state: electron in 1s
- Excited state: electron jumps to 2s or 2p
Atoms in the excited state usually fall back down to the ground state, giving off energy as light or heat.