[VISUAL] The photoelectron spectra for H and He are represented above. Which of the following statem — Atomic Structure Chemistry Question

STEPS:

1. Understand what photoelectron spectroscopy (PES) represents:
PES measures the binding energy (or ionization energy) of electrons in various subshells of an atom.
* The position of a peak along the horizontal (x) axis represents the binding energy of the electrons in a particular shell or subshell. Standard PES scales increase from right to left, meaning peaks located further to the left represent electrons that are more tightly attracted to the nucleus and have higher binding energies.
* The height of a peak along the vertical (y) axis is directly proportional to the relative number of electrons residing in that specific subshell.

2. Analyze the electron configurations of Hydrogen (H) and Helium (He):
* Hydrogen (atomic number 1) has the electron configuration $1s^1$, containing exactly one electron in its outer shell.
* Helium (atomic number 2) has the electron configuration $1s^2$, containing exactly two electrons in its outermost (valence) shell.

3. Account for the peak height difference:
* Because Helium possesses two valence electrons in its $1s$ subshell and Hydrogen possesses only one, Helium has twice as many electrons in this orbital.
* This stoichiometric difference dictates that the peak representing Helium's $1s$ subshell must be twice as high as the peak representing Hydrogen's $1s$ subshell.

4. Account for the peak position difference (shift to the left):
* Hydrogen has a nucleus containing one proton (nuclear charge of $+1$), while Helium has a nucleus containing two protons (nuclear charge of $+2$).
* The valence electrons for both elements reside in the same $1s$ energy level.
* Because Helium has a greater nuclear charge (more protons), it exerts a significantly stronger Coulombic attraction on its electrons than Hydrogen does.
* This stronger electrostatic attraction increases the binding energy of the electrons in Helium, making them more difficult to remove.
* Consequently, the peak for Helium is shifted further to the left on the PES energy scale.

5. Select the correct option:
* Option B correctly identifies both factors: Helium has a greater nuclear charge, which increases the attraction of its electrons to the nucleus, and has twice as many electrons in its $1s$ orbital.

*

WHY_OTHERS_WRONG:

• Option A is incorrect: Hydrogen has a nuclear charge of $+1$, which is *smaller* than Helium's nuclear charge of $+2$. If Hydrogen had a greater nuclear charge, its peak would be shifted to the left of Helium's, which is the opposite of the given PES spectra.
• Option C is incorrect: Although Helium contains two electrons in its $1s$ shell and experiences some electron-electron repulsion, the effect of its doubled nuclear charge ($2$ protons vs. $1$ proton) far outweighs any shielding or repulsion. As a result, the distance of the valence electrons from the nucleus is less in Helium, and its electrons have a *greater* binding energy, not a decreased binding energy.
• Option D is incorrect: Helium has two valence electrons in its outer shell, whereas Hydrogen has only one. Therefore, Hydrogen has *fewer* valence electrons than Helium, which would make its peak shorter (not taller) than Helium's.