U1.6 · Photoelectron Spectroscopy (PES)Practice · 光电子能谱（PES）

From left (high binding energy) to right, the five peaks are 1s, 2s, 2p, 3s, and 3p, with heights 2 : 2 : 6 : 2 : 1: [Ne]3s²3p¹, 13 electrons, which is Al. Na and Mg have only four peaks (3s¹ and 3s²), and Si’s 3p peak would be as tall as its 3s peak.

The two lowest-energy peaks are the outer shell (n = 3): 3s with height 2 and 3p with height 4, so 6 valence electrons. This is sulfur ([Ne]3s²3p⁴). Counting only the rightmost peak (4) misses the 3s electrons; 16 is the total number of electrons.

Both atoms’ 1s electrons are innermost and nearly unshielded, so their attraction depends mainly on nuclear charge. Ar has 18 protons and Ne 10, so Ar’s 1s electrons are held more tightly and sit closer in, with about 3.7 times the binding energy (data: LBNL X-ray Data Booklet). Both are noble gases, and 1s is n = 1 in both.

Na is [Ne]3s¹ (peak heights 2 : 2 : 6 : 1) and Mg is [Ne]3s² (2 : 2 : 6 : 2): both have four peaks (1s, 2s, 2p, 3s), and Mg’s 3s peak is twice as tall. With one more proton, every level in Mg is held more tightly, so each peak shifts to a higher binding energy (to the left).

Peak heights 2 : 2 : 6 : 2 : 5 mean 1s²2s²2p⁶3s²3p⁵, 17 electrons: chlorine. With 7 valence electrons, it gains 1 to reach argon’s configuration, forming $\ce{Cl-}$ with a charge of −1.