2 Electrons Shared Between Two Carbon Atoms (σ Bond)

In a C–C single bond, 2 shared electrons occupy the central face-to-face overlap directly along the internuclear axis to form 1 Sigma (σ) bond, revolving separately so they do not repel.

2 Sigma (σ) Electrons: Face-to-face overlap ALONG internuclear axis

2 Pi (π) Electrons: Side-by-side p-orbital bridge ABOVE & BELOW axis

Remaining Carbon Electrons (Core 1s² + Unshared Valence e⁻)

⚡ C–C SINGLE BOND: 1 SIGMA (σ) BOND (2 e⁻)

Bond Order: 1 | Length: 154 pm | Energy: 348 kJ/mol

🧲 Drag either Carbon atom left/right, or use the top tabs to explore Slides 2, 3 & 4!

🧲 C–C Distance:

Face-to-Face (σ) vs. Side-by-Side (π) Orbital Overlap

Face-to-Face (Head-On) Overlap meets directly on the internuclear axis to form a strong, rotatable Sigma (σ) bond. Side-by-Side (Parallel) Overlap bridges above and below the axis to form a rigid Pi (π) bond.

🧲 Drag the Overlap Slider below (or click Merge Orbitals) to watch Face-to-Face vs. Side-by-Side orbitals collide!

🟢 Face-to-Face (Head-On) → Sigma (σ) Bond

• 1 Overlap Zone directly ON the internuclear axis
• Stronger bond (greater direct overlap) & allows free rotation

2 e⁻ on Axis

🟡 Side-by-Side (Parallel) → Pi (π) Bond

• 2 Overlap Zones (Top + Bottom = 1 π bond, 0 density on axis)
• Weaker than σ (less overlap) & locks rotation (rigid plane)

2 e⁻ Above & Below

🔬 Orbital Distance:

How AP Chemistry Asks It: The σ & π Bond X-Ray Scanner

AP Exam Golden Rule: Every covalent bond starts with 1 Sigma (σ) bond. A Double Bond = 1σ + 1π, and a Triple Bond = 1σ + 2π. Never forget to count the C–H single bonds!

🟢 Sigma (σ) Bonds Scanned: 0

🟡 Pi (π) Bonds Scanned: 0

👆 Click any bond on the molecule to X-Ray scan it, or use "Scan Step-by-Step" below!

Single (—) = 1σ | Double (=) = 1σ + 1π | Triple (≡) = 1σ + 2π

The Bond Rotation Trap: C–C Axle vs. C=C Rigid Ladder Lock 🔄🚫

Why does C–C rotate freely while C=C is locked? A Sigma (σ) bond is a single central axle (twisting keeps 100% overlap), whereas a Pi (π) bond acts like two parallel ladder rails above & below — twisting 90° breaks the parallel p-orbital overlap!

🔄 Drag the Twist Angle Slider below (0° → 90°) to see why C–C spins like a wheel axle while C=C snaps its π ladder rails!

🛞 C–C Single Bond = "Single Wheel Axle" (Free Rotation)

• Head-on σ overlap is cylindrical along the internuclear axis
• Twisting one Carbon 90° or 180° causes 0% loss of overlap

Rotates Freely

🪜 C=C Double Bond = "Rigid Ladder Rails" (Rotation Locked!)

• Top & Bottom π bridges require parallel p-orbitals like ladder rails
• Twisting 90° makes p-orbitals perpendicular → breaks the π bond!

Cis / Trans Isomers

🔄 Twist Right Carbon (0°–90°): 0°

AP Exam Puzzle: Bond Order, Length & Energy Table (2e⁻ vs. 4e⁻ vs. 6e⁻) 📊⚡

Coulomb's Law Rule: More shared electrons between the nuclei (2e⁻ → 4e⁻ → 6e⁻) increases electrostatic attraction, pulling the Carbon nuclei closer (shorter length) and making the bond stronger (higher bond energy).

👆 Click any row in the AP Data Table (or switch between 2e⁻, 4e⁻, and 6e⁻ above) to watch the bond length shrink & energy rise!

Bond (Molecule)	Shared e⁻ (σ / π)	Length	Energy
C–C (C₂H₆)	2 e⁻ (1σ)	154 pm	348 kJ/mol
C=C (C₂H₄)	4 e⁻ (1σ + 1π)	134 pm	614 kJ/mol
C≡C (C₂H₂)	6 e⁻ (1σ + 2π)	120 pm	839 kJ/mol

📝 Official AP Exam Traps

A C–C single bond has a bond energy of 348 kJ/mol, while a C=C double bond has a bond energy of 614 kJ/mol (which is less than 2 × 348 = 696 kJ/mol). Which best explains why the second bond is weaker than the first?

💡 AP Exam Secret: 1st bond = Head-on σ (348 kJ/mol); 2nd bond = Side-by-side π (+266 kJ/mol) with less overlap!

More Shared e⁻ (2e⁻ → 4e⁻ → 6e⁻) = Higher Bond Order → Shorter Length → Higher Energy

Click Any Carbon to Reveal Its Hybridization (sp³ / sp² / sp) 🎯🧬

AP Exam Domain Rule: Only Sigma (σ) bonds + Lone Pairs count as electron domains! Each Pi (π) bond uses an unhybridized p-orbital: 4σ = sp³ (109.5°) • 3σ + 1π = sp² (120°) • 2σ + 2π = sp (180°).

👆 Click any Carbon atom (C₁, C₂, C₃…) on the molecule to inspect its σ domains, unhybridized p-orbitals, and hybridization!

🔍 Selected: Carbon C₁ (–CH₃) sp³ Hybridized

• Electron Domains: 4 σ bonds + 0 π bonds = 4 Domains
• Orbital Recipe: 4 sp³ hybrid orbitals + 0 unhybridized p-orbitals (Tetrahedral, 109.5°)

📝 Official AP Exam Style MCQ

In the molecule shown on the left (CH₃–CH=CH–C≡CH), what are the hybridizations of carbons C₁, C₂, and C₄, respectively?

💡 Teacher Tip: Click each Carbon atom on the left canvas or click ✨ Reveal All Carbon Hybridizations below!

sp³ = 4σ (0 unhybridized p) | sp² = 3σ + 1π (1 unhybridized p) | sp = 2σ + 2π (2 unhybridized p)

Live 4-Choice AP Exam MCQ Arena (With Visual Trap Explainer) 🏆📝

Click ANY option (A, B, C, or D) — even the wrong answers! Clicking a College Board distractor immediately triggers a live orbital animation on the left proving visually why that choice is a student trap!

🎯 Arena Ready: Click A, B, C, or D to Trigger Visual Proof!

⏱️ AP Pacing Timer: 60s

👆 Click any MCQ choice (A, B, C, or D) on the right (or the Trap buttons below) to watch the orbitals expose each misconception!

#1 AP Rule: Top Lobe + Bottom Lobe = ONE (1) π Bond = 2 Electrons Total!

The "AP FRQ Scoring Guideline" Builder (Earn the 1 Point) ✍️✅

Official AP Free-Response Prompt: "Explain in terms of atomic and hybrid orbitals how the σ (sigma) and π (pi) bonds form between the two carbon atoms in C₂H₄."

🟢 σ Rubric: Head-On sp²–sp² on Axis = VERIFIED

🏅 Official AP Reader Score: 1 / 1 Point ✅

👆 Click any of the 4 Official AP Rubric Checkboxes on the right to see which orbital part each buzzword lights up!

✍️ Student FRQ Booklet Response

✅ EARNS 1 / 1 POINT

In C₂H₄, the σ bond forms from the head-on (end-to-end) overlap of two sp² hybrid orbitals directly along the internuclear axis, while the π bond forms from the side-by-side (parallel) overlap of two unhybridized 2p orbitals above and below the axis.

📋 Official AP Reader Checklist (All 4 Required for 1 Point — Click to Toggle):

✓ 1. σ Orbital Identity: Names sp² hybrid orbitals on each Carbon

✓ 2. σ Overlap Geometry: States head-on / end-to-end overlap along the axis

✓ 3. π Orbital Identity: Names unhybridized p-orbitals on each Carbon

✓ 4. π Overlap Geometry: States side-by-side / parallel overlap above & below

🏅 AP Reader Scoring Note: All 4 buzzword elements are present and accurate → Full 1/1 Point Awarded!

AP FRQ Formula: Head-on sp²–sp² on axis = σ + Side-by-side unhybridized p–p above/below = π