Shells and the Periodic Table Photoelectron Spectroscopy

FIGURE 5.18 The energy of photoelectrons Is determined by measuring the voltage required to deflect the electrons along a semicircular pathway between two charged metallic hemispherical plates in vacuum so they arrive at the detector. 

FIGURE 5.19 Photoelectron spectrum of neon. The spectrum shows three peaks, demonstrating that the electrons of neon are organized in three bonding states of distinct energy values. The peak at 383.4 eV has been reduced by a factor of 4 for display on the same scale as the other two. 

These results are connected to the shell model by Koopmans s approximation, which asserts in a form suitable for our discussion that the ionization energy of an electron is the negative of the energy of the Hartree orbital of the electron  

These experimental results for neon are consistent with the electron configuration Ne ls 2s 2p predicted by the aufbau principle. Ionization energies measured in this way are used to construct the energy-level diagram for atoms and to show explicitly the value of the ground-state energy. 

FIGURE 5.20 Energy-level diagram of neon as determined by photoelectron spectroscopy. 

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