How do you turn an electron budget into a Lewis diagram?
You will be able to: Construct a simple Lewis diagram while conserving the electron count.
How do you turn an electron budget into a Lewis diagram?
Water has two H atoms attached to one O atom. Drawing H–O–H establishes who connects to whom; placing the remaining electrons completes the model.
A useful starting point: How many electrons belong in a Lewis diagram? →
Words and symbols before equations
- Skeleton
- The initial atom-connectivity pattern.
- Duet
- Two electrons around H in the usual stable Lewis picture.
- Octet
- Eight electrons around an atom in the common main-group model.
- Terminal atom
- An atom at the end of the skeleton.
What this picture assumes
Lewis connectivity, not 3D shape. A line is two electrons; dots are nonbonding electrons. H₂O has eight valence electrons. The skeleton stage is incomplete by design.
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 O–H bonds and two O lone pairs: eight electrons total. Connectivity diagram; water is bent in 3D.
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
Choose a plausible skeleton; H is terminal and usually forms one bond. Put a single bond between connected atoms, then count the electrons used.
Complete terminal shells, then place remaining electrons on the central atom. Check H for two and second-period C, N, O and F for no more than eight in ordinary closed-shell examples.
If the center lacks an octet, a terminal lone pair may need to become a multiple bond. Always recount the same original budget: drawing an extra line does not create electrons. A Lewis diagram shows electron accounting and connectivity, not a complete 3D geometry.
A worked example, step by step
Build H₂O using an eight-electron budget.
- Start with H–O–H, with oxygen central.
- Two single bonds use four electrons; four remain.
- Put the four remaining electrons into two lone pairs on O.
- O has eight nearby electrons (four bonding and four nonbonding); each H has two, and the whole diagram uses eight.
A flat H–O–H sketch does not establish that the molecule is linear; lone pairs matter for shape.
Do two O–H bonds alone use all eight electrons of water?
Compare with an explanation
No. They use four; the remaining four form two oxygen lone pairs.
Predict. Change one thing. Explain.
Reveal the skeleton, bonding pairs, then lone pairs. At every step compare electrons placed with the fixed total of eight.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
Two O–H bonds and two O lone pairs: eight electrons total. Connectivity diagram; water is bent in 3D.
Lewis connectivity, not 3D shape. A line is two electrons; dots are nonbonding electrons. H₂O has eight valence electrons. The skeleton stage is incomplete by design.
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 questionDraw NH₃ with N=5 and H=1. Give the total, bonds, lone pairs, and explain what the drawing alone cannot establish.
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Compare with the answer and four-point rubric
- 1 point: Budget = 5 + 3 = 8 electrons.
- 1 point: Three N–H bonds use six electrons.
- 1 point: One N lone pair uses two; N has an octet and each H a duet.
- 1 point: A Lewis diagram alone does not directly show its three-dimensional bond angles.
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 1What does a bond line represent?
Two shared electrons.
RECALL 2What should remain constant during construction?
The total valence-electron budget.
RECALL 3What does a Lewis diagram show most directly?
Connectivity and valence-electron accounting.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
How do you turn an electron budget into a Lewis diagram?
- Whole-species count: count each drawn electron once.
- Shell check: include both electrons of every adjacent bond.
Remember: A flat H–O–H sketch does not establish that the molecule is linear; lone pairs matter for shape.
Conditions: Lewis connectivity, not 3D shape. A line is two electrons; dots are nonbonding electrons. H₂O has eight valence electrons. The skeleton stage is incomplete by design.
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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