---
title: "A student models the bond energetics of \\(\\text{F}_2\\), \\(\\text{Cl}_2\\), and \\(\\text{Br}_2\\) using the potential-energy curves shown. The zero of potential energy represents completely separated atoms. The covalent radii increase in the order \\(\\text{F}"
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date_modified: "2026-08-21T08:41:28+00:00"
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# A student models the bond energetics of \(\text{F}_2\), \(\text{Cl}_2\), and \(\text{Br}_2\) using the potential-energy curves shown. The zero of potential energy represents completely separated atoms. The covalent radii increase in the order \(\text{F}

A student models the bond energetics of \(\text{F}_2\), \(\text{Cl}_2\), and \(\text{Br}_2\) using the potential-energy curves shown. The zero of potential energy represents completely separated atoms. The covalent radii increase in the order \(\text{F}<\text{Cl}<\text{Br}\), and the depth of a curve’s minimum below zero corresponds to the bond dissociation energy.

Which choice correctly assigns the curves and explains why the curve with the shortest equilibrium bond does not have the greatest bond dissociation energy?

![Draw a grayscale graph with light horizontal and vertical gridlines. The horizontal axis is labeled \(r\ (\text{pm})\), spans \(100\) to \(350\), and increases rightward. The vertical axis is labeled \(E_{\text{potential}}\ (\text{kJ mol}^{-1})\), spans \(-300\) to \(+250\), and increases upward. A legend maps a solid line to \(X\), a dashed line to \(Y\), and a dotted line to \(Z\). Each line rises very steeply above \(+200\) at short distance, descends through \(0\) to a single smooth minimum, and then approaches \(0\) from below as distance increases. Put the solid-line minimum at \((140,-160)\), the dashed-line minimum at \((200,-240)\), and the dotted-line minimum at \((230,-190)\). Mark each minimum with a small filled point. Make the minimum order and relative well depths unmistakable. No molecular sketches, arrows, explanatory annotations, or other text appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787301688-erN2oY.jpg)

- **A.** \(X=\text{F}_2\), \(Y=\text{Cl}_2\), and \(Z=\text{Br}_2\); the \(\text{F}-\text{F}\) bond is weaker because a shorter equilibrium bond necessarily permits less orbital overlap.
- **B.** \(X=\text{F}_2\), \(Y=\text{Br}_2\), and \(Z=\text{Cl}_2\); the \(\text{Br}-\text{Br}\) bond has the deepest well because the greater polarizability of \(\text{Br}\) strengthens London dispersion forces.
- **C.** \(X=\text{F}_2\), \(Y=\text{Cl}_2\), and \(Z=\text{Br}_2\); at the short \(\text{F}-\text{F}\) separation, repulsions between compact filled electron regions, especially adjacent lone pairs, offset more of the bonding attraction.
- **D.** \(X=\text{Br}_2\), \(Y=\text{Cl}_2\), and \(Z=\text{F}_2\); atoms with more core electrons experience greater repulsion and therefore have shorter equilibrium bond lengths.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120090/*