Apentix/AP Chemistry/Unit 1: Atomic Structure and Properties/Question
AP Chemistrymediummcq1 pt

Within the same electron shell of an atom, the 2s peak in a PES spectrum sits at higher binding energy than the 2p peak. Why?

A.2s electrons penetrate closer to the nucleus and feel less shielding
B.2s electrons sit farther from the nucleus
C.The 2s subshell holds more electrons
D.2p electrons experience a smaller nuclear charge

Explanation

Core Concept

Although 2s and 2p share the same shell, a 2s orbital's probability density leaks nearer the nucleus. That penetration lets 2s electrons dodge part of the shielding from other electrons and feel a stronger net attraction. Ejecting them therefore costs more energy, shifting the 2s peak toward higher binding energy.

Correct Answer

A2s electrons penetrate closer to the nucleus and feel less shielding

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