• $summary_{type}$: concept
• $word_{count}$: 170

The hydrogen energy level diagram shows horizontal lines at $E_n$ = -13.6/$n^2$ eV. Ground state (n=1) is at -13.6 eV, first excited state (n=2) at -3.4 eV, second excited state (n=3) at -1.51 eV, and ionization level (n=infinity) at 0 eV. The levels get closer together as n increases. Downward transitions (higher to lower n) emit photons — this is the emission spectrum (bright lines on dark background). Upward transitions absorb photons — absorption spectrum (dark lines on continuous background). Photon wavelength: 1/lambda = R*$Z^2$*(1/$n_f^2$ - 1/$n_i^2$). At room temperature, hydrogen atoms are in the ground state, so only Lyman series ($n_f$ = 1) absorption lines appear. The largest energy gap in any series is between consecutive levels (first line), and the smallest gap (series limit) is from n = infinity. Within a series, the first line has the longest wavelength and the series limit has the shortest.