Electronegativity difference is plotted against the average value of this quantity for a crystal in Mooser-Pearson diagrams. This quantity is used to help categorize the K, L, and M edges that are produced during X-ray absorption spectroscopy. Ionization energy is proportional to the squared ratio of effective nuclear charge and this quantity. The difference in the reciprocals of the squares of two values of this quantity is related to the emitted (*) wavelength by the hydrogen-specific Rydberg formula. Electron transitions to a region where this quantity is 1 and 2 are used to define the Lyman and Balmer series, respectively. This integer quantity is used to identify which energy (10[1])shell a bound electron is likely occupying. For 10 points, the letter n symbolizes the first of what four quantum numbers? ■END■