---
title: "sp Hybridization — AP Chem Definition & Exam Guide"
description: "sp hybridization mixes one s and one p orbital into two equivalent hybrids, giving linear geometry and 180° bond angles. Key to triple bonds on AP Chem."
canonical: "https://fiveable.me/ap-chem/key-terms/sp-hybridization"
type: "key-term"
subject: "AP Chemistry"
unit: "Unit 2"
---

# sp Hybridization — AP Chem Definition & Exam Guide

## Definition

sp hybridization is the mixing of one s orbital and one p orbital on a central atom to form two equivalent hybrid orbitals (each 50% s, 50% p character), producing a linear geometry with 180° bond angles and leaving two unhybridized p orbitals available for pi bonding.

## What It Is

sp hybridization happens when an atom blends one s orbital with one p orbital to make two identical hybrid [orbitals](/ap-chem/key-terms/orbitals "fv-autolink"). Each hybrid is half s character and half p character. Those two hybrids point in exactly opposite directions, which is why sp-hybridized atoms sit in a **linear** arrangement with **180° [bond angles](/ap-chem/unit-2/vsepr-bond-hybridization/study-guide/OslsAmh8LcVoqbpnjPAu "fv-autolink")**.

Here's the part the AP exam loves. Hybridizing only one of the three p orbitals leaves **two unhybridized p orbitals** behind. Those leftover p orbitals overlap side-by-side to form **pi bonds**. That's why sp hybridization shows up wherever you see triple bonds (like the carbons in acetylene, HC≡CH) or an atom with two double bonds (like the central carbon in CO₂). A quick shortcut you can trust on the exam is to count regions of electron [density](/ap-chem/key-terms/density "fv-autolink") around the atom. Two regions, whether they're bonds or lone pairs, means sp.

## Why It Matters

This term lives in **Topic 2.7 (VSEPR and Bond Hybridization)** in **[Unit 2](/ap-chem/unit-2 "fv-autolink"): Compound Structure and Properties**, supporting learning objective **2.7.A**. That objective asks you to connect Lewis diagrams, VSEPR theory, bond orders, and hybridization to explain a molecule's structural and electronic properties. sp hybridization is the bridge between two skills you've already built. VSEPR tells you that two electron domains repel each other into a linear shape, and hybridization explains *which orbitals* the atom actually uses to make that happen. It also explains where pi bonds come from, which connects directly to [bond order](/ap-chem/key-terms/bond-order "fv-autolink"), bond energy, and bond length comparisons. If you can identify sp hybridization, you can justify why a triple bond is shorter and stronger than a double or single bond.

## Connections

### Linear Molecular Geometry (Unit 2)

sp hybridization and [linear geometry](/ap-chem/key-terms/linear-geometry "fv-autolink") are two descriptions of the same situation. Two electron domains push apart to 180°, and the two sp hybrids are the orbitals that point in those opposite directions. If the question says linear with no lone pairs distorting things, think sp.

### Triple Bond & Acetylene (Unit 2)

A [triple bond](/ap-chem/key-terms/triple-bond "fv-autolink") is one sigma bond plus two pi bonds, and those two pi bonds come from the two unhybridized p orbitals left over after sp hybridization. Acetylene (HC≡CH) is the classic example, with both carbons sp-hybridized and the whole molecule perfectly linear.

### sp2 and sp3 Hybridization (Unit 2)

The pattern is just counting. Mixing in more p orbitals gives more hybrids and a wider spread of angles. sp gives 2 hybrids at 180°, sp² gives 3 at 120°, sp³ gives 4 at 109.5°. Each step up in hybridization means one fewer leftover p orbital for [pi bonding](/ap-chem/unit-3/intermolecular-forces/study-guide/aq9pSoNJoW70eCdben01 "fv-autolink").

### Bond Order and Bond Energy (Unit 2)

Under LO 2.7.A you compare relative bond energies using bond order. sp-hybridized atoms host the highest bond orders (triple bonds), so spotting sp hybridization lets you argue that a C≡C bond is shorter and stronger than C=C or C–C.

## On the AP Exam

sp hybridization is a multiple-choice staple. Common stems ask you to identify which species has an sp-hybridized central atom (CO₂ and HC≡CH are the go-to answers), to count sigma and pi bonds in acetylene (3 sigma, 2 pi), or to state the ideal bond angle for sp hybridization (180°). The trap answers usually mix up hybridization with bond count, so remember to count *electron domains*, not individual bonds. No released FRQ has asked for the term verbatim, but FRQs regularly hand you a Lewis structure and ask you to justify geometry, bond angles, or relative bond lengths. Naming the hybridization and the leftover p orbitals is exactly the kind of particulate-level reasoning that earns those points.

## sp Hybridization vs sp2 hybridization

Students mix these up because both involve double or multiple bonds. The difference is the number of electron domains. sp means two domains (linear, 180°, two unhybridized p orbitals, so it can support a triple bond or two double bonds). sp² means three domains (trigonal planar, 120°, only one unhybridized p orbital, so at most one pi bond). A carbon with one double bond and two single bonds is sp², not sp.

## Key Takeaways

- sp hybridization mixes one s orbital with one p orbital to form two equivalent hybrid orbitals, each with 50% s and 50% p character.
- An sp-hybridized atom has exactly two regions of electron density, giving a linear arrangement with 180° bond angles.
- Hybridizing only one p orbital leaves two unhybridized p orbitals, which form the two pi bonds in a triple bond or in two double bonds.
- Acetylene (HC≡CH) is the classic sp example, with two sp-hybridized carbons, 3 sigma bonds, and 2 pi bonds total.
- CO₂ is also sp-hybridized at carbon because two double bonds still count as just two electron domains.
- The shortcut for any hybridization question is to count electron domains on the atom: 2 means sp, 3 means sp², 4 means sp³.

## FAQs

### What is sp hybridization in AP Chem?

sp hybridization is the mixing of one s orbital and one p orbital to create two equivalent hybrid orbitals pointing 180° apart. It's tested in Topic 2.7 (Unit 2) and explains linear molecules like CO₂ and acetylene.

### Does sp hybridization always mean there's a triple bond?

No. A triple bond guarantees sp hybridization, but sp doesn't guarantee a triple bond. The carbon in CO₂ is sp-hybridized with two double bonds, and BeCl₂'s central atom is sp with only single bonds. What sp really means is two electron domains.

### How is sp hybridization different from sp2 hybridization?

sp has two electron domains (linear, 180°) and two leftover p orbitals for pi bonding, while sp² has three domains (trigonal planar, 120°) and only one leftover p orbital. Count the domains around the atom and the answer falls out.

### What is the bond angle for sp hybridization?

180°. The two sp hybrid orbitals point in exactly opposite directions, which is why sp-hybridized atoms produce linear geometry. This shows up as a direct multiple-choice question on the AP exam.

### How many sigma and pi bonds are in acetylene (HC≡CH)?

Acetylene has 3 sigma bonds (two C–H and one C–C) and 2 pi bonds (both inside the C≡C triple bond). Both carbons are sp-hybridized, and the two pi bonds come from their unhybridized p orbitals.

## Related Study Guides

- [2.7 VSEPR and Bond Hybridization](/ap-chem/unit-2/vsepr-bond-hybridization/study-guide/OslsAmh8LcVoqbpnjPAu)

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