When should a lone pair become a multiple bond?
You will be able to: Build CO₂ by redistributing electrons without changing the budget.
When should a lone pair become a multiple bond?
The initial O–C–O skeleton gives carbon only four nearby electrons. Oxygen has lone pairs available, so sharing additional pairs can complete carbon’s octet without adding any electrons.
A useful starting point: How do you turn an electron budget into a Lewis diagram? →
Words and symbols before equations
- Single bond
- One shared pair, drawn as one line.
- Double bond
- Two shared pairs between the same atoms.
- Redistribution
- Moving a pair in the drawing from a lone pair to a shared position.
- Electron domain
- One region around a central atom; a multiple bond counts as one region.
What this picture assumes
Lewis electron accounting for CO₂, total sixteen electrons. Initial single-bond sketch is not the completed preferred structure; multiple bonds redistribute existing pairs.
Read the picture in three steps
- Read the species and labels first. A Lewis line represents two electrons; a spatial stick indicates connectivity. Use the stated quantities and units for numerical comparisons.
- Two double bonds use 8 electrons; four oxygen lone pairs use 8. Carbon has an octet.
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
CO₂ has 4 + 2(6) = 16 valence electrons. Two initial single bonds use four, and completing oxygen octets uses the other twelve.
Carbon then has only four electrons around it. Convert one lone pair from each O into an additional C–O bond. The total remains sixteen.
The result O=C=O has two lone pairs on each oxygen, an octet on every atom, and zero formal charges. Multiple bonds contribute several electron pairs but occupy one direction each for VSEPR.
A worked example, step by step
Count the electrons in the completed O=C=O Lewis diagram.
- Two double bonds contain four shared pairs: 8 bonding electrons.
- Each O has two lone pairs: 4 electrons per O, or 8 total.
- Whole-species count = 8 + 8 = 16.
- Carbon has 8 electrons from its two double bonds, but just two surrounding bond directions.
Do not add electrons when adding bond lines; move existing lone pairs into the shared region.
Does making two double bonds require increasing the CO₂ budget to twenty?
Compare with an explanation
No. Existing lone-pair electrons are reassigned to bonding pairs.
Predict. Change one thing. Explain.
Compare the single-bond skeleton with the completed structure. Track carbon’s shell count while the overall electron total stays sixteen.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
Two double bonds use 8 electrons; four oxygen lone pairs use 8. Carbon has an octet.
Lewis electron accounting for CO₂, total sixteen electrons. Initial single-bond sketch is not the completed preferred structure; multiple bonds redistribute existing pairs.
Explain what you noticed: Answer the investigation prompt above. State one observation and explain it using electron accounting, electrostatic interactions or spatial geometry. Identify what the representation cannot tell you.
Apply the idea to a fresh problem Practice →Show what you understand.
Two original questions are a starting check, not proof of mastery. Explain your choice before revealing the answer.
Original written challenge
4 points · self-check · not an official AP questionFor N₂ (N contributes 5), build a triple-bond structure. Count its bonding electrons, lone pairs, and the electrons around each nitrogen.
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Compare with the answer and four-point rubric
- 1 point: Total budget = 10 electrons.
- 1 point: A triple bond uses 6 bonding electrons.
- 1 point: The remaining 4 form one lone pair on each N.
- 1 point: Each N has 6 shared plus 2 nonbonding electrons, giving an octet.
Accept equivalent correct methods and explanations. This is a Refresh Kid teaching rubric, not an official AP scoring guideline.
Retrieve it before you reveal it.
RECALL 1How many electrons are in a triple bond?
Six: three shared pairs.
RECALL 2Why can a lone pair become a bond?
It can complete a neighbor’s shell while conserving the total budget.
RECALL 3Does bond multiplicity equal domain count?
No. A multiple bond occupies one domain around the central atom.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
When should a lone pair become a multiple bond?
- CO₂ budget = 16 electrons.
- A double bond is two pairs but one VSEPR domain.
Remember: Do not add electrons when adding bond lines; move existing lone pairs into the shared region.
Conditions: Lewis electron accounting for CO₂, total sixteen electrons. Initial single-bond sketch is not the completed preferred structure; multiple bonds redistribute existing pairs.
Refresh Kid · AP Chemistry Unit 2 · Objectives 2.5.A · Review edition
Framework, scope and review status
Mapped to College Board CED, Topic 2.5, objectives 2.5.A. CED effective Fall 2024, current official file checked September 16, 2026, together with the published clarifications. This is Unit 2: Compound Structure and Properties, Topics 2.1–2.7. The focused lesson breakdown is Refresh Kid’s editorial sequence. Models and original practice are teaching materials, not official AP questions. Numerical potential curves, ion comparisons and orbital-alignment indices state their approximations. Five- and six-domain shapes are included; d-orbital hybridization and molecular-orbital diagrams are not required here. GitHub’s 3D website examples, including the Three.js Mars camera-control example, informed the use of rotatable scenes. Our scientific geometry and viewer code are original; no repository artwork or tutorial code was copied. The self-hosted Three.js library retains its MIT license. Camera rotation does not alter chemistry. See also the official clarifications.
Implementation and automated checks are separate from independent teacher review and observation of students. Both human review stages remain pending. This is a review edition, not a certified or validated assessment.
Optional further resource: College Board’s released questions and scoring guides. Papers can combine units; this link is an archive, not an assignment of every question to this lesson.
Our learn, explore, practice and recall sequence is informed by the IES learning guide. The exact Refresh Kid implementation has not been evaluated for learning effectiveness.
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