---
title: "A student examines the periodic properties of the Period \\(3\\) elements sodium (\\(\\text{Na}\\)), silicon (\\(\\text{Si}\\)), and chlorine (\\(\\text{Cl}\\)). Which of the following lists these elements in order of increasing first ionization energy, and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/119563/"
date_modified: "2026-08-21T06:53:45+00:00"
---

# A student examines the periodic properties of the Period \(3\) elements sodium (\(\text{Na}\)), silicon (\(\text{Si}\)), and chlorine (\(\text{Cl}\)). Which of the following lists these elements in order of increasing first ionization energy, and provides the correct justification?

A student examines the periodic properties of the Period \(3\) elements sodium (\(\text{Na}\)), silicon (\(\text{Si}\)), and chlorine (\(\text{Cl}\)). Which of the following lists these elements in order of increasing first ionization energy, and provides the correct justification?

- **A.** \(\text{Na} < \text{Si} < \text{Cl}\), because the effective nuclear charge increases across the period while the number of core electron shielding layers remains constant.
- **B.** \(\text{Na} < \text{Si} < \text{Cl}\), because the number of occupied principal energy levels increases across the period, decreasing the average distance from the nucleus to the valence electrons.
- **C.** \(\text{Cl} < \text{Si} < \text{Na}\), because the increased number of valence electrons in \(\text{Cl}\) causes greater electron-electron repulsion, making its valence electrons easiest to remove.
- **D.** \(\text{Cl} < \text{Si} < \text{Na}\), because \(\text{Na}\) has fewer core electrons than \(\text{Cl}\), resulting in less shielding and a stronger attraction to the nucleus.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119563/*