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</head>
<body>

  <div class="grid">
    
    <div class="tile active">
      <span class="badge-top">Total = 4</span>
      <svg viewBox="0 0 160 110">
        
        <line class="bond" x1="80" y1="42" x2="80" y2="24" />
        <line class="bond" x1="80" y1="68" x2="80" y2="86" />
        <line class="bond" x1="68" y1="55" x2="48" y2="55" />
        <line class="bond" x1="92" y1="55" x2="112" y2="55" />
        
        <text class="atom" x="80" y="55">C</text>
        <text class="atom atom-h" x="80" y="15">H</text>
        <text class="atom atom-h" x="80" y="95">H</text>
        <text class="atom atom-h" x="38" y="55">H</text>
        <text class="atom atom-h" x="122" y="55">H</text>
      </svg>
      <div>
        <div class="label">4 single bonds</div>
      </div>
    </div>

    
    <div class="tile">
      <span class="badge-top">Total = 4</span>
      <svg viewBox="0 0 160 110">
        
        <line class="bond" x1="69" y1="51" x2="91" y2="51" />
        <line class="bond" x1="69" y1="59" x2="91" y2="59" />
        
        <line class="bond" x1="51" y1="46" x2="38" y2="30" />
        <line class="bond" x1="51" y1="64" x2="38" y2="80" />
        
        <line class="bond" x1="109" y1="46" x2="122" y2="30" />
        <line class="bond" x1="109" y1="64" x2="122" y2="80" />
        
        <text class="atom" x="60" y="55">C</text>
        <text class="atom" x="100" y="55">C</text>
        <text class="atom atom-h" x="30" y="22">H</text>
        <text class="atom atom-h" x="30" y="88">H</text>
        <text class="atom atom-h" x="130" y="22">H</text>
        <text class="atom atom-h" x="130" y="88">H</text>
      </svg>
      <div>
        <div class="label">1 double + 2 singles</div>
      </div>
    </div>

    
    <div class="tile">
      <span class="badge-top">Total = 4</span>
      <svg viewBox="0 0 160 110">
        
        <line class="bond" x1="69" y1="48" x2="91" y2="48" />
        <line class="bond" x1="69" y1="55" x2="91" y2="55" />
        <line class="bond" x1="69" y1="62" x2="91" y2="62" />
        
        <line class="bond" x1="50" y1="55" x2="32" y2="55" />
        <line class="bond" x1="110" y1="55" x2="128" y2="55" />
        
        <text class="atom" x="60" y="55">C</text>
        <text class="atom" x="100" y="55">C</text>
        <text class="atom atom-h" x="22" y="55">H</text>
        <text class="atom atom-h" x="138" y="55">H</text>
      </svg>
      <div>
        <div class="label">1 triple + 1 single</div>
      </div>
    </div>

    
    <div class="tile">
      <span class="badge-top">Total = 4</span>
      <svg viewBox="0 0 160 110">
        
        <line class="bond" x1="44" y1="51" x2="70" y2="51" />
        <line class="bond" x1="44" y1="59" x2="70" y2="59" />
        
        <line class="bond" x1="90" y1="51" x2="116" y2="51" />
        <line class="bond" x1="90" y1="59" x2="116" y2="59" />
        
        <text class="atom atom-o" x="32" y="55">O</text>
        <text class="atom" x="80" y="55">C</text>
        <text class="atom atom-o" x="128" y="55">O</text>
      </svg>
      <div>
        <div class="label">2 double bonds</div>
      </div>
    </div>
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</body>
</html>

The Four Covalent Bonds of Carbon

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      font-size: 11px;
      font-weight: 700;
      text-anchor: middle;
      dominant-baseline: central;
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      font-size: 11px;
      font-weight: 700;
      text-anchor: middle;
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      gap: 12px;
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      max-width: 500px;
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      font-size: 13px;
      cursor: pointer;
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      background: #e2e8f0;
    }
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      display: flex;
      gap: 6px;
    }
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      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: background 0.2s;
    }
    .dot.active {
      background: #0284c7;
    }
  </style>
</head>
<body>

  <div class="header">
    <div class="title-badge">C₃H₆ Propene</div>
    <div class="stepper-nav">
      <button class="step-btn active" onclick="setStep(0)">1. Chain</button>
      <button class="step-btn" onclick="setStep(1)">2. Single</button>
      <button class="step-btn" onclick="setStep(2)">3. Double</button>
    </div>
  </div>

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    <div class="step-view active" id="view-0">
      <svg viewBox="0 0 400 200">
        
        <line class="bond" x1="125" y1="100" x2="180" y2="100" />
        <line class="bond" x1="220" y1="100" x2="275" y2="100" />
        
        <text class="atom-c" x="105" y="100">C</text>
        <text class="atom-c" x="200" y="100">C</text>
        <text class="atom-c" x="295" y="100">C</text>
      </svg>
    </div>

    
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        <line class="bond" x1="125" y1="100" x2="180" y2="100" />
        <line class="bond" x1="220" y1="100" x2="275" y2="100" />
        
        
        <line class="bond" x1="105" y1="84" x2="105" y2="52" />
        <line class="bond" x1="87" y1="100" x2="58" y2="100" />
        <text class="atom-h" x="105" y="42">H</text>
        <text class="atom-h" x="48" y="100">H</text>

        
        <line class="bond" x1="200" y1="84" x2="200" y2="52" />
        <line class="bond" x1="200" y1="116" x2="200" y2="148" />
        <text class="atom-h" x="200" y="42">H</text>
        <text class="atom-h" x="200" y="158">H</text>

        
        <line class="bond" x1="295" y1="84" x2="295" y2="52" />
        <line class="bond" x1="313" y1="100" x2="342" y2="100" />
        <text class="atom-h" x="295" y="42">H</text>
        <text class="atom-h" x="352" y="100">H</text>

        
        <text class="atom-c" x="105" y="100">C</text>
        <text class="atom-c" x="200" y="100">C</text>
        <text class="atom-c" x="295" y="100">C</text>

        
        <rect class="badge-bg-err" x="80" y="150" width="50" height="22" />
        <text class="badge-txt-err" x="105" y="161">3/4 ⚠️</text>

        <rect class="badge-bg-ok" x="175" y="172" width="50" height="22" />
        <text class="badge-txt-ok" x="200" y="183">4/4 ✓</text>

        <rect class="badge-bg-err" x="270" y="150" width="50" height="22" />
        <text class="badge-txt-err" x="295" y="161">3/4 ⚠️</text>
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    </div>

    
    <div class="step-view" id="view-2">
      <svg viewBox="0 0 400 200">
        
        <line class="bond-double" x1="125" y1="95" x2="180" y2="95" />
        <line class="bond-double" x1="125" y1="105" x2="180" y2="105" />

        
        <line class="bond" x1="220" y1="100" x2="275" y2="100" />

        
        <line class="bond" x1="90" y1="88" x2="62" y2="65" />
        <line class="bond" x1="90" y1="112" x2="62" y2="135" />
        <text class="atom-h" x="52" y="55">H</text>
        <text class="atom-h" x="52" y="145">H</text>

        
        <line class="bond" x1="200" y1="84" x2="200" y2="52" />
        <text class="atom-h" x="200" y="42">H</text>

        
        <line class="bond" x1="295" y1="84" x2="295" y2="52" />
        <line class="bond" x1="295" y1="116" x2="295" y2="148" />
        <line class="bond" x1="313" y1="100" x2="342" y2="100" />
        <text class="atom-h" x="295" y="42">H</text>
        <text class="atom-h" x="295" y="158">H</text>
        <text class="atom-h" x="352" y="100">H</text>

        
        <text class="atom-c" x="105" y="100">C</text>
        <text class="atom-c" x="200" y="100">C</text>
        <text class="atom-c" x="295" y="100">C</text>

        
        <rect class="badge-bg-ok" x="80" y="156" width="50" height="22" />
        <text class="badge-txt-ok" x="105" y="167">4/4 ✓</text>

        <rect class="badge-bg-ok" x="175" y="156" width="50" height="22" />
        <text class="badge-txt-ok" x="200" y="167">4/4 ✓</text>

        <rect class="badge-bg-ok" x="270" y="172" width="50" height="22" />
        <text class="badge-txt-ok" x="295" y="183">4/4 ✓</text>
      </svg>
    </div>
  </div>

  <div class="controls">
    <button class="ctrl-btn" onclick="prevStep()">◀</button>
    <button class="ctrl-btn" id="playBtn" onclick="togglePlay()">⏸</button>
    <button class="ctrl-btn" onclick="nextStep()">▶</button>
    <div class="dots">
      <div class="dot active" onclick="setStep(0)"></div>
      <div class="dot" onclick="setStep(1)"></div>
      <div class="dot" onclick="setStep(2)"></div>
    </div>
  </div>

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    function update() {
      for (let i = 0; i < 3; i++) {
        document.getElementById(`view-${i}`).classList.toggle('active', i === current);
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      timer = setInterval(() => {
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    startLoop();
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</body>
</html>

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<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
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      box-sizing: border-box;
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      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .header-title {
      font-size: 16px;
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      text-align: center;
      margin-bottom: 12px;
      color: #1e2945;
      letter-spacing: -0.2px;
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      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
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</head>
<body>

  <div class="header-title">Spot the Error: Carbon's Valence</div>

  <div class="comparison-grid">
    
    <div class="panel panel-incorrect">
      <div class="badge badge-error">✕ INCORRECT</div>

      <svg class="molecule-svg" viewBox="0 0 200 130">
        
        <circle cx="105" cy="65" r="16" fill="#fee2e2" stroke="#ef4444" stroke-width="1.5" stroke-dasharray="3 3" />

        
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        <circle cx="75" cy="65" r="7" class="num-bg-err" />
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        <line x1="119" y1="64" x2="154" y2="39" class="bond-line bond-incorrect" />
        <circle cx="127" cy="40" r="7" class="num-bg-err" />
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        <circle cx="143" cy="52" r="7" class="num-bg-err" />
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        <line x1="115" y1="74" x2="145" y2="95" class="bond-line bond-incorrect" />
        <circle cx="132" cy="86" r="7" class="num-bg-err" />
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        <line x1="102" y1="78" x2="92" y2="108" class="bond-line bond-incorrect" />
        <circle cx="95" cy="94" r="7" class="num-bg-err" />
        <text x="95" y="94" class="num-badge">5</text>

        
        <text x="36" y="65" class="atom-label atom-c">H₃C</text>
        <text x="105" y="65" class="atom-label atom-c">C</text>
        <text x="165" y="27" class="atom-label atom-o">O</text>
        <text x="156" y="105" class="atom-label atom-h">H</text>
        <text x="88" y="118" class="atom-label atom-h">H</text>
      </svg>

      <div class="callout callout-error">5 bonds (Max 4)</div>
    </div>

    
    <div class="panel panel-correct">
      <div class="badge badge-success">✓ CORRECT</div>

      <svg class="molecule-svg" viewBox="0 0 200 130">
        
        <circle cx="105" cy="65" r="16" fill="#dcfce7" stroke="#22c55e" stroke-width="1.5" />

        
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        <line x1="119" y1="64" x2="154" y2="39" class="bond-line bond-correct" />
        <circle cx="127" cy="40" r="7" class="num-bg-ok" />
        <text x="127" y="40" class="num-badge">2</text>
        <circle cx="143" cy="52" r="7" class="num-bg-ok" />
        <text x="143" y="52" class="num-badge">3</text>

        
        <line x1="115" y1="74" x2="145" y2="95" class="bond-line bond-correct" />
        <circle cx="132" cy="86" r="7" class="num-bg-ok" />
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        <text x="105" y="65" class="atom-label atom-c">C</text>
        <text x="165" y="27" class="atom-label atom-o">O</text>
        <text x="156" y="105" class="atom-label atom-h">H</text>
      </svg>

      <div class="callout callout-success">Exactly 4 bonds ✓</div>
    </div>
  </div>

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          <circle cx="80" cy="80" r="58" fill="none" stroke="#fb923c" stroke-width="1.5" opacity="0.4" />
          
          
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          <text x="80" y="77" fill="#f8fafc" font-size="10" font-weight="700" text-anchor="middle" dominant-baseline="central">6p</text>
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        4 valence electrons
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      <div class="card-title">Bonding Capacity</div>
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          <line x1="100" y1="80" x2="130" y2="80" stroke="#38bdf8" stroke-width="2.5" stroke-linecap="round" />
          <line x1="80" y1="100" x2="80" y2="130" stroke="#38bdf8" stroke-width="2.5" stroke-linecap="round" />
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          <circle cx="80" cy="80" r="18" fill="#0f172a" stroke="#38bdf8" stroke-width="1.5" />
          <text x="80" y="81" fill="#f8fafc" font-size="20" font-weight="800" text-anchor="middle" dominant-baseline="central">C</text>
          
          
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        4 bond sites<br><span style="font-size: 11px; font-weight: 500; opacity: 0.85;">(tetravalent)</span>
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UK-GCSE-SCIENCE-CHEM-SBM-03

Child standards (3)

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