---
title: "A student compares wires of identical length and cross-sectional area made from pure copper and from a copper-tin bronze alloy. In the bronze, the \\(\\text{Sn}\\) atoms occupy substitutional positions in the metallic \\(\\text{Cu}\\) lattice. At \\(298\\ \\text{K}\\), the student obtains the following results.  | Sample | Conductivity, \\(\\sigma\\) (\\(\\text{S}\\,\\text{m}^{-1}\\)) | |—|—:| | Pure \\(\\text{Cu}\\) | \\(5.9\\times10^{7}\\) | | \\(\\text{Cu}\\)-\\(\\text{Sn}\\) bronze | \\(1.0\\times10^{7}\\) |  A particulate model of each metallic solid is shown. Which statement best explains the observed difference in conductivity?"
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url: "https://nerd-notes.com/ubq/120094/"
date_modified: "2026-08-21T08:41:32+00:00"
---

# A student compares wires of identical length and cross-sectional area made from pure copper and from a copper-tin bronze alloy. In the bronze, the \(\text{Sn}\) atoms occupy substitutional positions in the metallic \(\text{Cu}\) lattice. At \(298\ \text{K}\), the student obtains the following results.

| Sample | Conductivity, \(\sigma\) (\(\text{S}\,\text{m}^{-1}\)) |
|—|—:|
| Pure \(\text{Cu}\) | \(5.9\times10^{7}\) |
| \(\text{Cu}\)-\(\text{Sn}\) bronze | \(1.0\times10^{7}\) |

A particulate model of each metallic solid is shown. Which statement best explains the observed difference in conductivity?

A student compares wires of identical length and cross-sectional area made from pure copper and from a copper-tin bronze alloy. In the bronze, the \(\text{Sn}\) atoms occupy substitutional positions in the metallic \(\text{Cu}\) lattice. At \(298\ \text{K}\), the student obtains the following results.

| Sample | Conductivity, \(\sigma\) (\(\text{S}\,\text{m}^{-1}\)) |
|---|---:|
| Pure \(\text{Cu}\) | \(5.9\times10^{7}\) |
| \(\text{Cu}\)-\(\text{Sn}\) bronze | \(1.0\times10^{7}\) |

A particulate model of each metallic solid is shown. Which statement best explains the observed difference in conductivity?

![A grayscale, \(2\)-panel particulate diagram. A legend centered above the panels maps an open circle to a \(\text{Cu}\) ion core, a larger gray circle to a \(\text{Sn}\) ion core, and a small solid dot to a representative delocalized electron. The left panel, labeled “Pure metal,” contains a rectangular \(4\)-by-\(5\) array of exactly \(20\) open circles with uniform horizontal and vertical spacing. Exactly \(8\) small solid dots appear in spaces between the rows without touching any circle. The right panel, labeled “Substitutional alloy,” contains the same \(4\)-by-\(5\) lattice positions. Exactly \(4\) positions—row \(1\), column \(4\); row \(2\), column \(2\); row \(3\), column \(5\); and row \(4\), column \(3\)—hold larger gray circles; the remaining \(16\) positions hold open circles. Exactly \(8\) small solid dots are dispersed between rows. Use bare axes-free panel boxes with no gridlines. No arrows, bonds, charges, or other annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787301692-kN2xmE.jpg)

- **A.** The bronze has lower conductivity because the greater molar mass of \(\text{Sn}\) causes its ion cores to remove more kinetic energy from delocalized electrons during collisions.
- **B.** The bronze has lower conductivity because differences in the sizes and electrostatic environments of the \(\text{Cu}\) and \(\text{Sn}\) ion cores disrupt the regular lattice and increase the scattering of delocalized electrons.
- **C.** The bronze has lower conductivity because \(\text{Sn}\) forms discrete covalent electron-pair bonds with neighboring \(\text{Cu}\) atoms, localizing the electrons that conduct electricity.
- **D.** The bronze has lower conductivity because the larger \(\text{Sn}\) atoms increase the average separation of the ion cores, weakening their attraction to the electron sea and decreasing the force that drives electrons through the wire.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120094/*