---
title: "Noncovalent Interactions — AP Chemistry Definition & Guide"
description: "Noncovalent interactions are the intermolecular forces (London dispersion, dipole-dipole, ion-dipole, hydrogen bonding) that set boiling points and hold biomolecules together on the AP Chem exam."
canonical: "https://fiveable.me/ap-chem/key-terms/noncovalent-interactions"
type: "key-term"
subject: "AP Chemistry"
unit: "Unit 3"
---

# Noncovalent Interactions — AP Chemistry Definition & Guide

## Definition

In AP Chemistry, noncovalent interactions are the attractive forces between molecules (or between regions of one large molecule) that don't share electrons, including London dispersion, dipole-dipole, ion-dipole, and hydrogen bonding.

## What It Is

Noncovalent interactions are the attractions that happen *between* molecules instead of *within* them. A [covalent bond](/ap-chem/key-terms/covalent-bond "fv-autolink") shares [electrons](/ap-chem/unit-1/atomic-structure-electron-configurations/study-guide/DiW6kVmwDRDakxKodjw5 "fv-autolink") to hold atoms together inside a molecule. Noncovalent interactions are weaker, and they pull separate molecules toward each other (or pull together different parts of one big molecule like a protein or DNA strand). The main types are London dispersion forces, dipole-dipole forces, ion-dipole forces, and hydrogen bonding.

All of these come from the same root cause: Coulombic attraction between partial or temporary charges. London dispersion forces show up in everything because electron clouds are always shifting, creating brief temporary dipoles (per [AP Chem](/ap-chem "fv-autolink") 3.1.A.1, they're often the *strongest* net force between large molecules because bigger, more polarizable electron clouds make them stronger). Dipole-dipole and hydrogen bonding need permanent polarity, and ion-dipole needs an actual ion. "Noncovalent interactions" is just the umbrella term that covers all of them, especially when chemists talk about biomolecules.

## Why It Matters

This sits in [Unit 3](/ap-chem/unit-3 "fv-autolink") (Properties of Substances and Mixtures), built on topics 3.1 (Intermolecular and Interparticle Forces) and 3.2 (Properties of Solids). The learning objective AP Chem 3.1.A asks you to connect a molecule's structure to the relative strength of its [intermolecular forces](/ap-chem/key-terms/intermolecular-forces "fv-autolink"), both for identical molecules and for two different species. AP Chem 3.2.A then pushes you to link those forces to macroscopic properties. Essential knowledge 3.2.A.1 spells out the payoff: because intermolecular forces are completely overcome during vaporization, boiling point and vapor pressure track directly with how strong those noncovalent interactions are. So this term is the bridge between what a molecule looks like on paper and how it behaves in a beaker.

## Connections

### [London Dispersion Forces (Unit 3)](/ap-chem/key-terms/london-dispersion-forces)

These are the floor that every [molecule](/ap-chem/unit-2/lewis-diagrams/study-guide/KjqTRYr5TVr2C3Be3u0J "fv-autolink") has. Even nonpolar molecules attract each other because electron clouds flicker into temporary dipoles, and bigger clouds (more electrons, more pi bonding) flicker harder, so dispersion can quietly become the dominant noncovalent interaction in large molecules.

### [Hydrogen Bonding (Unit 3)](/ap-chem/key-terms/hydrogen-bonding)

The strongest of the standard noncovalent interactions, and the reason water boils so high for its tiny size. On the exam it's the headline force holding the two strands of a DNA double helix together and stabilizing protein shapes.

### Boiling Point and Vapor Pressure (Unit 3)

Stronger noncovalent interactions mean a higher [boiling point](/ap-chem/key-terms/boiling-point "fv-autolink") and lower vapor pressure, because you have to dump in more energy to fully separate the molecules. This is the most common way the exam asks you to *use* intermolecular forces instead of just naming them.

### [Ion-Dipole Forces (Unit 3)](/ap-chem/key-terms/ion-dipole-forces)

The reason ionic compounds dissolve in water. The full ion [charge](/ap-chem/unit-9 "fv-autolink") tugs hard on the partial charges of polar solvent molecules, which is why this term reaches into solubility and solution questions, not just pure-substance properties.

## On the AP Exam

Multiple-choice stems love to make you rank substances by boiling point, melting point, or vapor pressure, and the trick is to identify which noncovalent interactions are present and which is strongest. Practice questions also stretch this term into biology-flavored contexts: stabilizing a DNA double helix, holding a protein's tertiary or quaternary structure together, or driving an enzyme binding to its substrate. You may even see a thermodynamics twist where a given ΔH° and ΔS° point you toward which type of interaction is at work. No released FRQ uses "noncovalent interactions" word-for-word, but free-response prompts regularly ask you to draw particulate-level pictures (as in EK 3.2.A.2) and explain a property like boiling point in terms of the forces between particles. Your job is always to name the force AND explain it using molecular structure.

## noncovalent interactions vs Covalent bonds

Covalent bonds hold atoms together *inside* a molecule by sharing electrons, and they're strong. Noncovalent interactions act *between* molecules and are much weaker, so they're the ones broken when something boils or when a protein denatures. When a liquid vaporizes, you overcome noncovalent interactions, not covalent bonds. The covalent bonds inside each molecule stay intact.

## Key Takeaways

- Noncovalent interactions are the intermolecular forces between molecules, covering London dispersion, dipole-dipole, ion-dipole, and hydrogen bonding.
- They all trace back to Coulombic attraction between partial or temporary charges, just at different strengths.
- London dispersion forces exist in every substance and can be the strongest net force in large, highly polarizable molecules.
- Because vaporization fully overcomes these forces, boiling point and vapor pressure directly track their strength.
- Noncovalent interactions also hold biomolecules together, like the two strands of DNA and the folded shape of a protein.
- On the exam, name the force AND justify it using molecular structure, don't just label it.

## FAQs

### What are noncovalent interactions in AP Chemistry?

They're the attractive forces between molecules (or between regions of one large molecule) that don't involve sharing electrons. The four you need are London dispersion, dipole-dipole, ion-dipole, and hydrogen bonding, and they all come from Coulombic attraction between charges or partial charges.

### Are noncovalent interactions the same as intermolecular forces?

Yes, essentially. "Noncovalent interactions" is just the broader name often used when discussing biomolecules, but in AP Chem Unit 3 it refers to the same set of intermolecular forces: London dispersion, dipole-dipole, ion-dipole, and hydrogen bonding.

### How are noncovalent interactions different from covalent bonds?

Covalent bonds share electrons to hold atoms together inside a single molecule and are strong. Noncovalent interactions act between separate molecules and are much weaker, which is why boiling or denaturing a protein breaks the noncovalent interactions while leaving the covalent bonds intact.

### Which noncovalent interaction is the strongest?

Among the standard four, hydrogen bonding is the strongest, followed by dipole-dipole, then London dispersion (ion-dipole is also very strong because a full ion charge is involved). But for large molecules, London dispersion can add up to be the dominant net force because polarizability grows with electron count.

### Why do noncovalent interactions affect boiling point?

Boiling means fully separating molecules from each other, so you have to overcome all the noncovalent interactions holding them together. Per essential knowledge 3.2.A.1, stronger interactions mean a higher boiling point and lower vapor pressure.

## Related Study Guides

- [3.1 Intermolecular and Interparticle Forces](/ap-chem/unit-3/intermolecular-forces/study-guide/aq9pSoNJoW70eCdben01)

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