A PES spectrum shows three peaks with relative heights 2 : 2 : 6, from highest to lowest binding energy. Which element is it?
ACarbon
BOxygen
CNeon
DSodium
Heights 2, 2 and 6 match 1s², 2s² and 2p⁶, which is neon. Carbon and oxygen would show smaller 2p peaks, and sodium would add a fourth peak for 3s¹.
Question 2 True / False
In a PES spectrum, the tallest peak always corresponds to the electrons with the highest binding energy.
TTrue
FFalse
Answer: False
Peak height is proportional to the number of electrons in a subshell. In neon, the 2p peak is tallest because it holds six electrons, yet it has the lowest binding energy.
Question 3 Multiple Choice
How does the 1s peak of sodium compare with the 1s peak of neon?
ASame binding energy, same height
BHigher binding energy, same height
CLower binding energy, same height
DHigher binding energy, three times the height
Both 1s subshells hold two electrons, so the heights match. Sodium has one more proton, so its 1s electrons are held more tightly and the peak appears at higher binding energy.
Question 4 Short Answer
Explain how PES data support the idea that the second shell is divided into subshells.
Think about your answer, then reveal below.
Model answer: Electrons in the second shell give two separate peaks, not one. The 2s peak lies at higher binding energy than the 2p peak, and their heights (2 and up to 6) match the capacities of the s and p subshells.
If all n = 2 electrons had the same energy, they would give one peak. The split into two peaks with these height ratios is direct evidence for s and p subshells.