---
title: "Covalent Bonding — AP Chem Definition & Catalysis Guide"
description: "Covalent bonding is the sharing of electrons between atoms. In AP Chem it underlies Unit 2 bonding and explains how catalysts form intermediates in Topic 5.11."
canonical: "https://fiveable.me/ap-chem/key-terms/covalent-bonding"
type: "key-term"
subject: "AP Chemistry"
unit: "Unit 5"
---

# Covalent Bonding — AP Chem Definition & Catalysis Guide

## Definition

Covalent bonding is the sharing of electron pairs between atoms to form a chemical bond. On the AP Chem exam it appears as a core bonding concept and again in Topic 5.11, where some catalysts speed up reactions by covalently bonding to a reactant to form a reaction intermediate.

## What It Is

Covalent bonding is what happens when two atoms share [electrons](/ap-chem/unit-1/atomic-structure-electron-configurations/study-guide/DiW6kVmwDRDakxKodjw5 "fv-autolink") instead of transferring them. The shared pair sits between the nuclei, both atoms are attracted to it, and that attraction holds the atoms together. Breaking a [covalent bond](/ap-chem/key-terms/covalent-bond "fv-autolink") costs energy, and forming one releases energy. That energy bookkeeping is why bond strength shows up constantly on the exam.

In [Unit 5](/ap-chem/unit-5 "fv-autolink"), covalent bonding gets a second job. Under EK 5.11.A.3, some catalysts work by *covalently bonding* to a reactant, creating a new species called a reaction intermediate. That intermediate then reacts along a different pathway with a lower activation energy than the uncatalyzed route. So the same electron-sharing idea you learned for Lewis structures becomes the actual mechanism by which a catalyst rewrites a reaction's path. The catalyst forms a bond, the intermediate does its thing, and the catalyst is regenerated unchanged at the end.

## Why It Matters

This term lives in [Topic 5.11](/ap-chem/unit-5/catalysts/study-guide/bkTgdolcJRgD7fG434Ru "fv-autolink") (Catalysis) in Unit 5 and supports learning objective 5.11.A, which asks you to explain how a [catalyst](/ap-chem/key-terms/catalyst "fv-autolink") changes a reaction mechanism. The CED gives you three main ways catalysts work, and covalent bonding to form an intermediate is one of them (alongside acid-base catalysis and surface catalysis). If you can spot the mechanism step where the catalyst covalently bonds a reactant, you can explain why the catalyzed path has a lower activation energy, why the rate increases, and why the catalyst's net concentration stays constant (5.11.A.2). Covalent bonding is also foundational chemistry from the bonding unit, so understanding it well pays off across the whole course.

## Connections

### [Reaction Intermediate (Unit 5)](/ap-chem/key-terms/reaction-intermediate)

This is the direct link. When a catalyst covalently bonds to a reactant, the new species it creates is a [reaction intermediate](/ap-chem/key-terms/reaction-intermediate "fv-autolink"). The intermediate appears in the mechanism but cancels out of the overall equation, just like the catalyst does.

### [Activation Energy (Unit 5)](/ap-chem/key-terms/activation-energy)

Forming a covalent bond with the catalyst opens a new reaction pathway with a lower [activation energy](/ap-chem/key-terms/activation-energy "fv-autolink") than the original route. The reaction is faster not because molecules move faster, but because the energy hill they have to climb got shorter.

### [Effective Collisions (Unit 5)](/ap-chem/key-terms/effective-collisions)

Per 5.11.A.1, a catalyst must increase [effective collisions](/ap-chem/key-terms/effective-collisions "fv-autolink") and/or lower activation energy. Covalent catalysis does the second one by holding a reactant in a bonded intermediate that reacts more easily.

### Types of Chemical Bonds (Unit 2)

Unit 2 is where covalent bonding gets its full treatment, including Lewis structures, bond polarity, and bond energy. The Haber process question type leans on this. Nitrogen's triple bond is extremely strong (945 kJ/mol in the gas phase), which is exactly why an iron catalyst surface is needed to weaken it.

## On the AP Exam

No released FRQ has used "covalent bonding" verbatim in the catalysis context, but it shows up in multiple-choice stems built around mechanisms. A typical question gives you the acid-catalyzed hydrolysis of an ester and asks which step shows the catalyst forming a reaction intermediate through covalent bonding. Another classic move is the Haber process. You're told N2 + 3H2 → 2NH3 barely happens at room temperature but races on an iron surface, and you have to explain that the catalyst provides a lower-energy pathway for breaking that 945 kJ/mol N-N bond. Your job on these questions is to (1) identify which mechanism step involves the catalyst bonding to a reactant, (2) label the resulting species as an intermediate, and (3) confirm the catalyst is regenerated later so its net concentration is unchanged.

## covalent bonding vs Ionic bonding

Covalent bonding is sharing electrons between atoms (usually two nonmetals). Ionic bonding is a full transfer of electrons that creates oppositely charged ions held together by electrostatic attraction (usually metal + nonmetal). In catalysis questions, the CED specifically says some catalysts bind reactants covalently, meaning a real shared-electron bond forms in the intermediate, not just an electrostatic attraction.

## Key Takeaways

- Covalent bonding means two atoms share electron pairs, and the attraction of both nuclei to the shared pair holds the bond together.
- In Topic 5.11, some catalysts speed up reactions by covalently bonding to a reactant, forming a reaction intermediate that reacts along a lower-energy pathway.
- Even when a catalyst covalently bonds to a reactant, it is regenerated in a later step, so its net concentration never changes (EK 5.11.A.2).
- A catalyzed pathway works by lowering activation energy or increasing effective collisions, per EK 5.11.A.1, not by changing the overall reaction or its thermodynamics.
- Strong covalent bonds like nitrogen's 945 kJ/mol triple bond explain why some reactions, like the Haber process, are negligibly slow without a catalyst.

## FAQs

### What is covalent bonding in AP Chem?

Covalent bonding is the sharing of electrons between atoms to form a chemical bond. It's foundational in the bonding unit and reappears in Topic 5.11, where some catalysts covalently bond to reactants to form intermediates.

### Does a catalyst get used up when it covalently bonds to a reactant?

No. The catalyst is often consumed in an early step (sometimes the rate-determining step) but is regenerated in a later step, so its net concentration stays constant per EK 5.11.A.2. If it weren't regenerated, it would be a reactant, not a catalyst.

### What's the difference between covalent and ionic bonding?

Covalent bonds share electrons between atoms, while ionic bonds transfer electrons completely, creating ions held together by electrostatic attraction. Catalysis questions about intermediates specifically involve covalent bonds, where the catalyst and reactant share electrons in a new species.

### How does covalent bonding relate to catalysis on the AP exam?

EK 5.11.A.3 says some catalysts accelerate reactions by covalently binding to a reactant to form a reaction intermediate. Multiple-choice questions often show a mechanism, like acid-catalyzed ester hydrolysis, and ask you to identify the step where that covalent bond forms.

### Why does the Haber process need an iron catalyst?

The N-N triple bond is extremely strong, about 945 kJ/mol in the gas phase, so the uncatalyzed reaction is negligibly slow at room temperature. The iron surface provides a pathway with a lower activation energy, making bond breaking feasible.

## Related Study Guides

- [5.11 Catalysis](/ap-chem/unit-5/catalysts/study-guide/bkTgdolcJRgD7fG434Ru)

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