---
title: "A student compares the first ionization energies and valence-electron configurations of two pairs of Period 3 elements.  | Element | Valence-electron configuration | First ionization energy \\(\\text{(kJ/mol)}\\) | |—|—|—:| | \\(\\text{Mg}\\) | \\([\\text{Ne}]3s^2\\) | \\(738\\) | | \\(\\text{Al}\\) | \\([\\text{Ne}]3s^2 3p^1\\) | \\(578\\) | | \\(\\text{P}\\) | \\([\\text{Ne}]3s^2 3p^3\\) | \\(1{,}012\\) | | \\(\\text{S}\\) | \\([\\text{Ne}]3s^2 3p^4\\) | \\(1{,}000\\) |  The student observes that the first ionization energy decreases from \\(\\text{Mg}\\) to \\(\\text{Al}\\) and from \\(\\text{P}\\) to \\(\\text{S}\\). Which row correctly predicts the electronegativity comparison for each pair?"
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url: "https://nerd-notes.com/ubq/119355/"
date_modified: "2026-08-19T12:39:57+00:00"
---

# A student compares the first ionization energies and valence-electron configurations of two pairs of Period 3 elements.

| Element | Valence-electron configuration | First ionization energy \(\text{(kJ/mol)}\) |
|—|—|—:|
| \(\text{Mg}\) | \([\text{Ne}]3s^2\) | \(738\) |
| \(\text{Al}\) | \([\text{Ne}]3s^2 3p^1\) | \(578\) |
| \(\text{P}\) | \([\text{Ne}]3s^2 3p^3\) | \(1{,}012\) |
| \(\text{S}\) | \([\text{Ne}]3s^2 3p^4\) | \(1{,}000\) |

The student observes that the first ionization energy decreases from \(\text{Mg}\) to \(\text{Al}\) and from \(\text{P}\) to \(\text{S}\). Which row correctly predicts the electronegativity comparison for each pair?

A student compares the first ionization energies and valence-electron configurations of two pairs of Period 3 elements.

| Element | Valence-electron configuration | First ionization energy \(\text{(kJ/mol)}\) |
|---|---|---:|
| \(\text{Mg}\) | \([\text{Ne}]3s^2\) | \(738\) |
| \(\text{Al}\) | \([\text{Ne}]3s^2 3p^1\) | \(578\) |
| \(\text{P}\) | \([\text{Ne}]3s^2 3p^3\) | \(1{,}012\) |
| \(\text{S}\) | \([\text{Ne}]3s^2 3p^4\) | \(1{,}000\) |

The student observes that the first ionization energy decreases from \(\text{Mg}\) to \(\text{Al}\) and from \(\text{P}\) to \(\text{S}\). Which row correctly predicts the electronegativity comparison for each pair?

- **A.** \(\chi(\text{Al})<\chi(\text{Mg})\) ; \(\chi(\text{S})<\chi(\text{P})\)
- **B.** \(\chi(\text{Al})<\chi(\text{Mg})\) ; \(\chi(\text{S})>\chi(\text{P})\)
- **C.** \(\chi(\text{Al})>\chi(\text{Mg})\) ; \(\chi(\text{S})<\chi(\text{P})\)
- **D.** \(\chi(\text{Al})>\chi(\text{Mg})\) ; \(\chi(\text{S})>\chi(\text{P})\)

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119355/*