---
title: "Covalent Bond — AP Chemistry Definition & Exam Guide"
description: "A covalent bond forms when atoms share valence electrons. Learn how bond order, bond length, and the potential energy curve show up on the AP Chem exam."
canonical: "https://fiveable.me/ap-chem/key-terms/covalent-bond"
type: "key-term"
subject: "AP Chemistry"
unit: "Unit 2"
---

# Covalent Bond — AP Chemistry Definition & Exam Guide

## Definition

A covalent bond is a chemical bond formed when two atoms share valence electrons, typically between nonmetals with similar electronegativities; its length depends on atomic size and bond order, with higher-order bonds (double, triple) being shorter and stronger (AP Chem Topics 2.1-2.2).

## What It Is

A covalent bond forms when two atoms share [valence electrons](/ap-chem/unit-1/valence-electrons-ionic-compounds/study-guide/XTtinEfGPR0jEJmpUuBx "fv-autolink") instead of transferring them. This usually happens between nonmetals, because both atoms pull on [electrons](/ap-chem/unit-1/atomic-structure-electron-configurations/study-guide/DiW6kVmwDRDakxKodjw5 "fv-autolink") with similar strength. If the electronegativities are nearly equal (like C and H), the sharing is even and the bond is **nonpolar covalent**. If one atom pulls harder, the sharing is lopsided and you get a **polar covalent** bond with partial charges.

The AP exam also wants you to think about covalent bonds in terms of energy and distance. Picture two atoms approaching each other. As they get closer, attraction between each [nucleus](/ap-chem/key-terms/nucleus "fv-autolink") and the shared electrons lowers the potential energy, until nucleus-nucleus repulsion takes over and the energy shoots back up. The bottom of that curve marks the **equilibrium bond length**, and the depth of the well is the **bond energy**. Bond length is set by two things, the size of each atom's core and the bond order. Triple bonds are shorter and stronger than double bonds, which are shorter and stronger than single bonds (EK 2.2.A.2).

## Why It Matters

[Covalent bonding](/ap-chem/key-terms/covalent-bonding "fv-autolink") lives in **[Unit 2](/ap-chem/unit-2 "fv-autolink"): Compound Structure and Properties**, specifically Topic 2.1 (Types of Chemical Bonds) and Topic 2.2 (Intramolecular Force and Potential Energy). It directly supports two learning objectives. **2.1.A** asks you to explain how the elements in a bond determine the bond type, using electronegativity trends and Coulomb's law. **2.2.A** asks you to interpret the potential energy vs. internuclear distance graph, reading off equilibrium bond length and bond energy. Covalent bonding is also the foundation everything else in Unit 2 is built on. Lewis structures, formal charge, resonance, VSEPR geometry, and polarity all assume you can first identify and describe a covalent bond.

## Connections

### [Polar Covalent Bond (Unit 2)](/ap-chem/key-terms/polar-covalent-bond)

Covalent bonding is a spectrum, not a switch. Equal sharing gives a nonpolar bond, unequal sharing gives a polar bond with partial charges, and a huge [electronegativity](/ap-chem/key-terms/electronegativity "fv-autolink") gap tips you into ionic territory. The exam loves asking you to place a specific bond on that spectrum.

### [Coulomb's Law (Units 1-2)](/ap-chem/key-terms/coulombs-law)

[Coulomb's law](/ap-chem/key-terms/coulombs-law "fv-autolink") explains why covalent bonds exist at all. The shared electrons sit between two nuclei and attract both, and that attraction is what lowers the potential energy. It also explains the periodic trends in electronegativity that decide whether a bond is covalent in the first place.

### Potential Energy and Internuclear Distance (Unit 2)

The PE vs. distance curve is the standard exam representation of a covalent bond. The minimum of the curve gives you the [bond length](/ap-chem/key-terms/bond-length "fv-autolink"), and the well depth gives you the bond energy. Stronger bonds mean deeper wells and shorter equilibrium distances.

### [Molecular Geometry (Unit 2)](/ap-chem/key-terms/molecular-geometry)

Once you know which atoms are covalently bonded, VSEPR takes over. Covalent bonds and lone pairs repel each other, and that repulsion sets the molecule's shape, which then determines whether the whole molecule is polar.

## On the AP Exam

Covalent bonding shows up in both MCQs and FRQs, and it's almost never just "define covalent bond." Multiple-choice stems ask you to pick the most nonpolar bond from a set of element pairs (pure electronegativity reasoning), to interpret how potential energy changes as internuclear distance changes, or to explain why an ionic compound and a covalent compound with similar electronegativity differences have wildly different melting points. On FRQs, covalent bonding is usually the entry point to a multi-part structure question. The 2021 long FRQ on silicon compounds and a long FRQ on the chromate ion CrO₄²⁻ both started by treating bonds as covalent, then built toward Lewis structures, bond order, and bond length comparisons. The reliable move to practice is the bond order argument. Higher bond order means shorter bond and larger bond energy, and you should be able to justify that from a Lewis structure.

## covalent bond vs Ionic bond

Covalent bonds share electrons; ionic bonds transfer them. Covalent bonds form between atoms of similar electronegativity (usually two nonmetals), while ionic bonds form between atoms with a large electronegativity difference (usually a metal and a nonmetal), creating cations and anions held together by Coulombic attraction. Watch out for the classic trap, though. Electronegativity difference alone doesn't settle it. The AP exam has asked why two compounds with the same electronegativity difference (1.9) have melting points of 801°C and 115°C. The answer is that one is actually ionic and one is covalent, so you have to use properties as evidence, not just the difference value.

## Key Takeaways

- A covalent bond is the sharing of valence electrons between atoms, typically two nonmetals with similar electronegativities.
- Equal sharing makes a nonpolar covalent bond, and unequal sharing makes a polar covalent bond; C-H bonds count as effectively nonpolar even though carbon is slightly more electronegative.
- On a potential energy vs. internuclear distance graph, the minimum marks the equilibrium bond length and the well depth equals the bond energy.
- Higher bond order means a shorter, stronger bond, so a triple bond is shorter and has a larger bond energy than a double or single bond between the same atoms.
- Bond length also depends on atomic size, so bonds between atoms with larger cores are longer.
- Electronegativity difference suggests bond type, but physical properties like melting point are the real evidence the exam expects you to cite.

## FAQs

### What is a covalent bond in AP Chemistry?

It's a bond formed when two atoms share valence electrons, usually between nonmetals with similar electronegativities. In Topics 2.1 and 2.2 you describe it using electronegativity, bond order, bond length, and the potential energy vs. internuclear distance graph.

### How is a covalent bond different from an ionic bond?

Covalent bonds share electrons between atoms; ionic bonds transfer electrons to form ions held together by Coulombic attraction. Covalent compounds tend to have much lower melting points, which is why the exam treats a 115°C melting point as evidence of covalent bonding and 801°C as evidence of ionic bonding.

### Are all covalent bonds nonpolar?

No. Only bonds between atoms of similar electronegativity are nonpolar (like C-H). When one atom is noticeably more electronegative, the electrons sit closer to it and the bond is polar covalent, with partial positive and negative charges.

### Why are triple bonds shorter than single bonds?

More shared electron pairs means more attraction pulling the two nuclei together, so the equilibrium bond length shrinks and the bond energy grows. This is EK 2.2.A.2, and 'higher bond order, shorter and stronger' is a phrase worth memorizing for FRQs.

### What does the potential energy curve for a covalent bond show?

It plots potential energy against internuclear distance. The lowest point on the curve gives the equilibrium bond length, and the energy needed to climb out of that well and separate the atoms is the bond energy. Be ready to read both values off a graph on the exam.

## Related Study Guides

- [2.2 Intramolecular Force and Potential Energy ](/ap-chem/unit-2/intramolecular-force-potential-energy/study-guide/2ybBItwMrCkB9MAOO9lC)

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