Question

 A photoelectron spectrum of a compound containing nitrogen (N), aluminium (Al), and fluorine (F) shows three strong peaks at the following binding energies:

Peak X: ~686 eV

Peak Y: ~399 eV

Peak Z: ~73 eV

Find the best option from the choices given below that best explains the relative positioning of these peaks in terms of binding energy.

(i) Peak X corresponds to F 1s electrons, which have the highest binding energy because fluorine’s high electronegativity and small size give its 1s electrons a large effective nuclear attraction. Peak Y is N 1s and Peak Z is Al 2p.

(ii) Nitrogen has more valence electrons than fluorine or aluminium, therefore its peak appears at the highest binding energy.

(iii) The spectrum shows more aluminium atoms than nitrogen or fluorine, so its peak appears at the lowest binding energy due to dilution.

(iv) Aluminium has the highest nuclear charge, so its 2p peak should have the largest binding energy, but shielding effects reverse this trend.
Justify your answer. 

21 Jan 2026
Answer :
Word Count : 271
In photoelectron spectroscopy, the binding energy of an electron depends primarily on the effective nuclear charge experienced by that electron, the principal quantum number of the orbital, and the shielding by inner electrons. Core electrons that are closer to the nucleus and experience a higher effective nuclear attraction exhibit higher binding energies, while electrons in outer shells or higher subshells have lower binding energies. Fluorine has atomic number 9 and a very small atomic radius, with its 1s electrons located extremely close to the nucleus. Due to poor shielding
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