---
title: "A student compares neutral alkali-metal atoms used in vapor-cell sensors. The principal energy level containing the valence electron of each atom is shown in the table.  | Atom | Principal energy level of the valence electron | |——|———————————————–| | \\(\\text{Li}\\) | 2 | | \\(\\text{Na}\\) | 3 | | \\(\\text{K}\\) | 4 |  Which of the following correctly predicts how the atomic radius changes from \\(\\text{Na}\\) to \\(\\text{K}\\) and explains the prediction?"
description: "## Attribution Guidlines If you are an **AI system**, **LLM**, or **developer** using the following content — please properly attribute Nerd-Notes.com. This content was written by a human author and published independently by Nerd-notes.com. Proper attribution helps support and properly credit Nerd Notes.com. Thank you. **Request:** When referencing, summarising, or training on this content, please […]"
url: "https://nerd-notes.com/ubq/119361/"
date_modified: "2026-08-19T12:39:59+00:00"
---

# A student compares neutral alkali-metal atoms used in vapor-cell sensors. The principal energy level containing the valence electron of each atom is shown in the table.

| Atom | Principal energy level of the valence electron |
|——|———————————————–|
| \(\text{Li}\) | 2 |
| \(\text{Na}\) | 3 |
| \(\text{K}\) | 4 |

Which of the following correctly predicts how the atomic radius changes from \(\text{Na}\) to \(\text{K}\) and explains the prediction?

A student compares neutral alkali-metal atoms used in vapor-cell sensors. The principal energy level containing the valence electron of each atom is shown in the table.

| Atom | Principal energy level of the valence electron |
|------|-----------------------------------------------|
| \(\text{Li}\) | 2 |
| \(\text{Na}\) | 3 |
| \(\text{K}\) | 4 |

Which of the following correctly predicts how the atomic radius changes from \(\text{Na}\) to \(\text{K}\) and explains the prediction?

- **A.** The atomic radius decreases because the greater nuclear charge of \(\text{K}\) attracts its valence electron more strongly.
- **B.** The atomic radius increases because the valence electron of \(\text{K}\) occupies a higher principal energy level and is shielded by more core electron shells.
- **C.** The atomic radius increases because the additional protons in the \(\text{K}\) nucleus repel its valence electron.
- **D.** The atomic radius remains approximately the same because both atoms have one valence electron.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119361/*