How does ammonia change when it accepts a proton?
You will be able to: Connect a nitrogen lone pair, protonation, charge and molecular shape.
How does ammonia change when it accepts a proton?
Compare ammonia, NH₃, with ammonium, NH₄⁺. One extra proton creates an additional N–H bond and changes the arrangement from a trigonal pyramid to a tetrahedron.
A useful starting point: Why is one hydrogen easier to donate than another? →
Words and symbols before equations
- Lone pair
- A nonbonding pair of valence electrons available on NH₃ nitrogen.
- Protonation
- Acceptance of H⁺ by a base.
- Trigonal pyramidal
- Three bonded atoms form a pyramid around a central atom with a lone pair.
- Tetrahedral
- Four bonded atoms point toward the corners of a tetrahedron.
What this picture assumes
Dilute ideal-solution concentration model at 25 °C, Kw=1.00×10⁻¹⁴. Concentrations are mol/L (M); displayed values are rounded. No household experiments are required. Original schematic molecular geometry, not measured coordinates or a trajectory. Bond lengths and sphere sizes are not to scale. The pair conserves N₁O₁H₆ and total charge +1; the nitrogen shape changes from pyramidal to tetrahedral.
Read the picture in three steps
- Read the species and labels first. Identify what each symbol and line represents. Read the units and fixed conditions before comparing quantities.
- Before transfer: NH₃ has three N–H bonds and a lone pair; H₃O⁺ has three O–H bonds. Count N₁O₁H₆ and total charge +1. The lone pair is explained in words, not drawn as an atom.
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
Ammonia’s nitrogen lone pair can form a bond to an incoming proton. In NH₃+H₃O⁺→NH₄⁺+H₂O, ammonia accepts H⁺ and hydronium donates it.
NH₃ has three N–H bonds and one lone pair. NH₄⁺ has four N–H bonds with no remaining nitrogen lone pair in its usual Lewis structure; this explains the different molecular shapes.
Count N, O and H across the whole displayed pair: one N, one O and six H on either side. The total charge is +1 on either side. Only the proton’s attachment changes in the bookkeeping.
The optional rotatable geometry helps you inspect an atom hidden behind another. The two selectable states are schematic endpoints, not a simulated trajectory or proof that a reaction proceeds in one elementary collision. Weak basicity is an equilibrium property, not simply a shape label.
A worked example, step by step
For NH₃+H₃O⁺→NH₄⁺+H₂O, identify the acid and base, verify conservation, and compare nitrogen shapes.
- NH₃ accepts H⁺, so it is the base; H₃O⁺ donates H⁺, so it is the acid.
- Each side has N₁O₁H₆.
- Total charge is +1 on each side.
- Nitrogen changes from three bonds plus a lone pair (pyramidal) to four bonds (tetrahedral).
Proton transfer adds H⁺, not a neutral H atom. Charge must be tracked along with atom counts.
Does NH₄⁺ retain the same nitrogen lone pair as NH₃?
Compare with an explanation
No. That electron pair now participates in the additional N–H bond.
Predict. Change one thing. Explain.
Switch the molecular pair before and after proton transfer. Rotate the optional 3D view to find every H, then explain the new N–H bond using the labeled 2D view as well.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
Before transfer: NH₃ has three N–H bonds and a lone pair; H₃O⁺ has three O–H bonds. Count N₁O₁H₆ and total charge +1. The lone pair is explained in words, not drawn as an atom.
Dilute ideal-solution concentration model at 25 °C, Kw=1.00×10⁻¹⁴. Concentrations are mol/L (M); displayed values are rounded. No household experiments are required. Original schematic molecular geometry, not measured coordinates or a trajectory. Bond lengths and sphere sizes are not to scale. The pair conserves N₁O₁H₆ and total charge +1; the nitrogen shape changes from pyramidal to tetrahedral.
Explain what you noticed: Answer the investigation prompt above. State one observation and explain it using proton transfer, charge and atom conservation, a mole balance or the stated acid–base equilibrium. 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 questionDescribe NH₃ protonation by H₃O⁺ using atom counts, charge, the nitrogen electron pair and molecular shape. Explain what rotation can and cannot show.
This response is not submitted or saved. Copy it before leaving.
Compare with the answer and four-point rubric
- 1 point: N₁O₁H₆ and total charge +1 are conserved.
- 1 point: Nitrogen’s lone pair forms an additional N–H bond.
- 1 point: NH₃ is pyramidal and NH₄⁺ tetrahedral.
- 1 point: Rotation reveals spatial arrangement, not reaction kinetics or a measured molecular trajectory.
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 1Which species gains a proton?
NH₃.
RECALL 2Why does nitrogen’s shape change?
Its lone pair becomes a fourth bonding pair.
RECALL 3Does camera rotation change the chemistry?
No; it changes only the view.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
How does ammonia change when it accepts a proton?
- NH₃ + H₃O⁺ → NH₄⁺ + H₂O.
- NH₃: trigonal pyramidal; NH₄⁺: tetrahedral.
Remember: Proton transfer adds H⁺, not a neutral H atom. Charge must be tracked along with atom counts.
Conditions: Dilute ideal-solution concentration model at 25 °C, Kw=1.00×10⁻¹⁴. Concentrations are mol/L (M); displayed values are rounded. No household experiments are required. Original schematic molecular geometry, not measured coordinates or a trajectory. Bond lengths and sphere sizes are not to scale. The pair conserves N₁O₁H₆ and total charge +1; the nitrogen shape changes from pyramidal to tetrahedral.
Refresh Kid · AP Chemistry Unit 8 · Objectives 8.6.A · Review edition
Framework, scope and review status
Mapped to College Board CED, Topic 8.6, objective 8.6.A. CED effective Fall 2024 and June 2026 clarifications checked September 17, 2026. Unit 8: Acids and Bases, Topics 8.1–8.11. Focused lesson names, examples, models and assessments are original Refresh Kid teaching materials, not additional official topics or official AP questions. Official corrections.
The model states its assumptions beside the diagram. Dilute ideal-solution concentrations approximate activities; numerical models use 25 °C and Kw=1.00×10⁻¹⁴ unless another pKw is supplied. pH need not be restricted to 0–14 in all real solutions. The optional 3D views show original schematic molecular geometry, not a measured trajectory or a reaction mechanism. Computation of a buffer’s pH change after adding acid/base, derivation of Henderson–Hasselbalch, concentrations of every species in a polyprotic titration, and solubility as a function of pH are excluded from assessed scope. Buffer response and pH-dependent solubility are taught qualitatively. Calculating the pH of a buffer formed by partial neutralization remains in Topic 8.4 scope.
Teaching resources: The Organic Chemistry Tutor video titles/descriptions and topic coverage were checked for optional links; no claim is made to have watched every video. No creator scripts, examples, worksheets or artwork were copied. GitHub’s 3D website collection and its Three.js camera-control example informed the idea of controllable spatial inspection. Scientific diagrams, geometry and interactions here are original. The self-hosted Three.js runtime retains its MIT license. Camera rotation changes the view, not the chemistry.
Independent teacher review and observation of students remain pending. Implementation checks do not certify scientific accuracy, accessibility or learning effectiveness. This is a review edition.
Optional official resource: Released AP Chemistry questions and scoring guides. This archive contains questions across units; it is not an assignment of every question to this lesson.
The teaching sequence is informed by the IES learning guide; this exact implementation has not been evaluated with learners.
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