<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
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      color: #1e293b;
      padding: 10px 14px;
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      flex-direction: column;
      gap: 12px;
      user-select: none;
      max-width: 540px;
      margin: 0 auto;
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    .section {
      display: flex;
      flex-direction: column;
      gap: 4px;
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    .section-header {
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      justify-content: space-between;
      align-items: center;
      padding-bottom: 2px;
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      font-weight: 700;
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      letter-spacing: 0.6px;
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      border-radius: 6px;
      padding: 5px 12px;
      font-size: 12px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      transition: background-color 0.2s, opacity 0.2s;
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    .btn:hover {
      opacity: 0.9;
    }
    .btn:focus-visible {
      outline: 2px solid #2563eb;
      outline-offset: 2px;
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    .btn.off {
      background: #64748b;
    }
    .btn-indicator {
      display: inline-block;
      width: 7px;
      height: 7px;
      border-radius: 50%;
      background: #4ade80;
    }
    .btn.off .btn-indicator {
      background: #cbd5e1;
    }
    svg {
      width: 100%;
      height: auto;
      display: block;
    }
    .plate-pos { fill: #fee2e2; stroke: #ef4444; stroke-width: 1.5; }
    .plate-neg { fill: #dbeafe; stroke: #3b82f6; stroke-width: 1.5; }
    .plate-text { font-size: 13px; font-weight: 800; text-anchor: middle; dominant-baseline: central; }
    .beam {
      fill: none;
      stroke: #10b981;
      stroke-width: 3.5;
      stroke-linecap: round;
      transition: d 0.4s ease;
      filter: drop-shadow(0 0 4px rgba(16, 185, 129, 0.7));
    }
    .beam-dot {
      fill: #10b981;
      transition: cx 0.4s ease, cy 0.4s ease;
    }
    .divider {
      height: 1px;
      background: #e2e8f0;
      margin: 2px 0;
    }
  </style>
</head>
<body>

  
  <div class="section">
    <div class="section-header">
      <span class="title">1. Cathode Ray Tube Experiment</span>
      <button id="toggleFieldBtn" class="btn" aria-label="Toggle electric field">
        <span class="btn-indicator"></span>
        <span id="btnText">Electric Field: ON</span>
      </button>
    </div>
    
    <svg viewBox="0 0 400 145">
      <defs>
        <linearGradient id="tubeGrad" x1="0%" y1="0%" x2="0%" y2="100%">
          <stop offset="0%" stop-color="#f8fafc" stop-opacity="0.9" />
          <stop offset="100%" stop-color="#f1f5f9" stop-opacity="0.9" />
        </linearGradient>
      </defs>

      
      <path d="M 38 46 L 105 46 L 345 22 C 362 22 370 38 370 70 C 370 102 362 118 345 118 L 105 94 L 38 94 C 30 94 30 46 38 46 Z" 
            fill="url(#tubeGrad)" stroke="#94a3b8" stroke-width="1.5" />

      
      <rect x="46" y="52" width="6" height="36" rx="2" fill="#475569" stroke="#334155" stroke-width="0.5" />
      <line x1="30" y1="70" x2="46" y2="70" stroke="#64748b" stroke-width="1.5" />
      
      <text x="49" y="32" font-size="10" font-weight="700" fill="#475569" text-anchor="middle">Cathode (−)</text>
      <line x1="49" y1="36" x2="49" y2="48" stroke="#94a3b8" stroke-width="1" stroke-dasharray="2,2" />

      
      <rect x="98" y="50" width="6" height="13" rx="1.5" fill="#475569" stroke="#334155" stroke-width="0.5" />
      <rect x="98" y="77" width="6" height="13" rx="1.5" fill="#475569" stroke="#334155" stroke-width="0.5" />
      
      <text x="101" y="116" font-size="10" font-weight="700" fill="#475569" text-anchor="middle">Anode (+)</text>
      <line x1="101" y1="104" x2="101" y2="92" stroke="#94a3b8" stroke-width="1" stroke-dasharray="2,2" />

      
      <g id="platesGroup" style="transition: opacity 0.3s ease;">
        
        <rect x="170" y="24" width="75" height="13" rx="3" class="plate-pos" />
        <text x="207.5" y="30.5" class="plate-text" fill="#dc2626">+</text>
        <text x="207.5" y="14" font-size="9" font-weight="700" fill="#dc2626" text-anchor="middle">Positive Plate (+)</text>
        
        
        <rect x="170" y="103" width="75" height="13" rx="3" class="plate-neg" />
        <text x="207.5" y="109.5" class="plate-text" fill="#2563eb">−</text>
        <text x="207.5" y="128" font-size="9" font-weight="700" fill="#2563eb" text-anchor="middle">Negative Plate (−)</text>
      </g>

      
      <path id="rayPath" class="beam" d="M 52 70 L 102 70 Q 195 70 364 40" />
      <circle id="rayGlow" class="beam-dot" cx="364" cy="40" r="4.5" />
      
      
      <path d="M 363 30 L 363 110" stroke="#10b981" stroke-width="3" stroke-linecap="round" opacity="0.35" />
      <text x="375" y="136" font-size="9.5" fill="#047857" font-weight="700" text-anchor="end">Deflection Screen</text>
    </svg>
  </div>

  <div class="divider"></div>

  
  <div class="section">
    <div class="section-header">
      <span class="title">2. Thomson's Plum Pudding Model</span>
    </div>
    
    <svg viewBox="0 0 400 135">
      
      <circle cx="200" cy="68" r="54" fill="#fee2e2" stroke="#f87171" stroke-width="2" />
      
      
      <g transform="translate(170, 48)">
        <circle cx="0" cy="0" r="9" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
        <text x="0" y="0" font-size="11" font-weight="800" fill="#ffffff" text-anchor="middle" dominant-baseline="central">−</text>
      </g>
      <g transform="translate(225, 50)">
        <circle cx="0" cy="0" r="9" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
        <text x="0" y="0" font-size="11" font-weight="800" fill="#ffffff" text-anchor="middle" dominant-baseline="central">−</text>
      </g>
      <g transform="translate(197, 72)">
        <circle cx="0" cy="0" r="9" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
        <text x="0" y="0" font-size="11" font-weight="800" fill="#ffffff" text-anchor="middle" dominant-baseline="central">−</text>
      </g>
      <g transform="translate(167, 85)">
        <circle cx="0" cy="0" r="9" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
        <text x="0" y="0" font-size="11" font-weight="800" fill="#ffffff" text-anchor="middle" dominant-baseline="central">−</text>
      </g>
      <g transform="translate(230, 82)">
        <circle cx="0" cy="0" r="9" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
        <text x="0" y="0" font-size="11" font-weight="800" fill="#ffffff" text-anchor="middle" dominant-baseline="central">−</text>
      </g>
      <g transform="translate(200, 40)">
        <circle cx="0" cy="0" r="8" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
        <text x="0" y="0" font-size="10" font-weight="800" fill="#ffffff" text-anchor="middle" dominant-baseline="central">−</text>
      </g>

      
      
      <line x1="120" y1="36" x2="160" y2="48" stroke="#dc2626" stroke-width="1.2" stroke-dasharray="3,2" />
      <text x="12" y="32" font-size="10" font-weight="700" fill="#dc2626" text-anchor="start">Uniform sphere of</text>
      <text x="12" y="46" font-size="10" font-weight="700" fill="#dc2626" text-anchor="start">positive charge (+)</text>

      
      <line x1="275" y1="64" x2="240" y2="80" stroke="#2563eb" stroke-width="1.2" stroke-dasharray="3,2" />
      <text x="280" y="60" font-size="10" font-weight="700" fill="#2563eb" text-anchor="start">Negatively charged</text>
      <text x="280" y="74" font-size="10" font-weight="700" fill="#2563eb" text-anchor="start">electrons (−)</text>
    </svg>
  </div>

  <script>
    const btn = document.getElementById('toggleFieldBtn');
    const btnText = document.getElementById('btnText');
    const path = document.getElementById('rayPath');
    const glow = document.getElementById('rayGlow');
    const plates = document.getElementById('platesGroup');
    let fieldOn = true;

    btn.addEventListener('click', () => {
      fieldOn = !fieldOn;
      if (fieldOn) {
        btnText.textContent = 'Electric Field: ON';
        btn.classList.remove('off');
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        glow.setAttribute('cy', '40');
        plates.style.opacity = '1';
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        btn.classList.add('off');
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        glow.setAttribute('cx', '364');
        glow.setAttribute('cy', '70');
        plates.style.opacity = '0.2';
      }
    });
  </script>
</body>
</html>

Historical Development of Atomic Models: Dalton to Bohr

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Rutherford's Gold Foil Experiment</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8fafc;
      color: #0f172a;
      padding: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 8px;
      user-select: none;
    }

    .toggle-bar {
      display: flex;
      background: #e2e8f0;
      border-radius: 20px;
      padding: 3px;
      gap: 4px;
      max-width: 100%;
    }

    .toggle-btn {
      border: none;
      background: transparent;
      padding: 6px 14px;
      border-radius: 16px;
      font-size: 12px;
      font-weight: 700;
      color: #334155;
      cursor: pointer;
      transition: background 0.2s ease, color 0.2s ease, box-shadow 0.2s ease;
    }

    .toggle-btn.active {
      background: #ffffff;
      color: #0369a1;
      box-shadow: 0 1px 4px rgba(0,0,0,0.15);
    }

    .panels {
      display: flex;
      width: 100%;
      max-width: 660px;
      gap: 10px;
      flex-wrap: wrap;
      justify-content: center;
    }

    .panel {
      flex: 1 1 290px;
      max-width: 325px;
      background: #ffffff;
      border: 1px solid #cbd5e1;
      border-radius: 10px;
      overflow: hidden;
      display: flex;
      flex-direction: column;
      align-items: center;
      position: relative;
    }

    .panel-label {
      width: 100%;
      text-align: center;
      font-size: 12px;
      font-weight: 800;
      text-transform: uppercase;
      letter-spacing: 0.6px;
      color: #0f172a;
      padding: 7px 0;
      background: #e2e8f0;
      border-bottom: 1px solid #cbd5e1;
    }

    .canvas-container {
      width: 100%;
      position: relative;
    }

    canvas {
      display: block;
      width: 100%;
      height: 240px;
      background: #090d16;
    }

    .legend {
      width: 100%;
      display: flex;
      justify-content: space-around;
      padding: 5px 6px;
      background: #f1f5f9;
      font-size: 11px;
      font-weight: 600;
      color: #1e293b;
      border-top: 1px solid #e2e8f0;
    }

    .legend-item {
      display: flex;
      align-items: center;
      gap: 4px;
    }

    .indicator {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      display: inline-block;
    }
    .ind-beam { background: #38bdf8; }
    .ind-foil { background: #eab308; border-radius: 2px; }
    .ind-screen { background: #22c55e; }
    .ind-nucleus { background: #ef4444; }

    @media (max-width: 400px) {
      .panel { max-width: 100%; }
      .toggle-btn { padding: 5px 10px; font-size: 11px; }
      canvas { height: 210px; }
      .legend { font-size: 10px; }
    }
  </style>
</head>
<body>

  <div class="toggle-bar">
    <button id="btn-rutherford" class="toggle-btn active" onclick="setModel('rutherford')">Rutherford (Actual)</button>
    <button id="btn-thomson" class="toggle-btn" onclick="setModel('thomson')">Thomson (Expected)</button>
  </div>

  <div class="panels">
    <div class="panel">
      <div class="panel-label">GOLD FOIL EXPERIMENT</div>
      <div class="canvas-container">
        <canvas id="macroCanvas"></canvas>
      </div>
      <div class="legend">
        <div class="legend-item"><span class="indicator ind-beam"></span> &alpha; Beam</div>
        <div class="legend-item"><span class="indicator ind-foil"></span> Gold Foil</div>
        <div class="legend-item"><span class="indicator ind-screen"></span> Flashes</div>
      </div>
    </div>

    <div class="panel">
      <div class="panel-label">ATOMIC SCALE</div>
      <div class="canvas-container">
        <canvas id="microCanvas"></canvas>
      </div>
      <div class="legend">
        <div class="legend-item"><span class="indicator ind-nucleus"></span> <span id="nucleus-label">Dense Nucleus (+2e)</span></div>
        <div class="legend-item"><span class="indicator ind-beam"></span> &alpha; Particle (+2)</div>
      </div>
    </div>
  </div>

  <script>
    let mode = 'rutherford'; // 'rutherford' | 'thomson'

    const macroCanvas = document.getElementById('macroCanvas');
    const microCanvas = document.getElementById('microCanvas');
    const macroCtx = macroCanvas.getContext('2d');
    const microCtx = microCanvas.getContext('2d');
    const nucleusLabel = document.getElementById('nucleus-label');

    function resizeCanvases() {
      const dpr = window.devicePixelRatio || 1;
      [macroCanvas, microCanvas].forEach(c => {
        const rect = c.getBoundingClientRect();
        c.width = rect.width * dpr;
        c.height = rect.height * dpr;
      });
    }

    window.addEventListener('resize', resizeCanvases);
    resizeCanvases();

    function setModel(m) {
      mode = m;
      document.getElementById('btn-rutherford').classList.toggle('active', m === 'rutherford');
      document.getElementById('btn-thomson').classList.toggle('active', m === 'thomson');
      nucleusLabel.textContent = m === 'rutherford' ? 'Dense Nucleus (+)' : 'Diffuse Sphere (+)';
      macroParticles = [];
      microParticles = [];
      flashes = [];
    }

    // --- MACRO SIMULATION ---
    let macroParticles = [];
    let flashes = [];
    let macroSpawnTimer = 0;

    function updateMacro(ctx, w, h) {
      ctx.clearRect(0, 0, w, h);

      const cx = w * 0.52;
      const cy = h * 0.5;
      const screenR = Math.min(w, h) * 0.42;

      // Detection screen (Circular Arc: ~40 deg to 320 deg)
      ctx.beginPath();
      ctx.arc(cx, cy, screenR, 0.28 * Math.PI, 1.72 * Math.PI, true);
      ctx.strokeStyle = '#15803d';
      ctx.lineWidth = 6;
      ctx.stroke();

      ctx.beginPath();
      ctx.arc(cx, cy, screenR, 0.28 * Math.PI, 1.72 * Math.PI, true);
      ctx.strokeStyle = '#4ade80';
      ctx.lineWidth = 2.5;
      ctx.stroke();

      // Screen detection glow ring
      ctx.beginPath();
      ctx.arc(cx, cy, screenR, 0.28 * Math.PI, 1.72 * Math.PI, true);
      ctx.strokeStyle = 'rgba(74, 222, 128, 0.15)';
      ctx.lineWidth = 12;
      ctx.stroke();

      // Gold Foil (Center vertical target)
      ctx.shadowColor = 'rgba(234, 179, 8, 0.4)';
      ctx.shadowBlur = 8;
      ctx.fillStyle = '#eab308';
      ctx.fillRect(cx - 2, cy - screenR * 0.78, 4, screenR * 1.56);
      ctx.fillStyle = '#fef08a';
      ctx.fillRect(cx - 0.5, cy - screenR * 0.78, 1, screenR * 1.56);
      ctx.shadowBlur = 0;

      // Alpha Emitter (Lead collimator box)
      const emX = w * 0.1;
      const emY = cy;
      ctx.fillStyle = '#64748b';
      ctx.fillRect(emX - 16, emY - 14, 22, 28);
      ctx.fillStyle = '#1e293b';
      ctx.fillRect(emX - 14, emY - 12, 18, 24);
      // Lead aperture / slit
      ctx.fillStyle = '#0f172a';
      ctx.fillRect(emX + 2, emY - 3, 6, 6);

      // Subtle main beam glow guide
      const beamGrad = ctx.createLinearGradient(emX, cy, cx, cy);
      beamGrad.addColorStop(0, 'rgba(56, 189, 248, 0.35)');
      beamGrad.addColorStop(1, 'rgba(56, 189, 248, 0.1)');
      ctx.fillStyle = beamGrad;
      ctx.fillRect(emX + 6, cy - 2, cx - (emX + 6), 4);

      // Spawn Alpha Particles at a steady, readable pace
      macroSpawnTimer++;
      if (macroSpawnTimer % 7 === 0) {
        macroParticles.push({
          x: emX + 6,
          y: emY + (Math.random() - 0.5) * 2,
          vx: 1.45, // Slowed down so traversal takes > 1.2s (>500ms)
          vy: 0,
          deflected: false,
          trail: []
        });
      }

      // Update & Draw Macro Particles
      for (let i = macroParticles.length - 1; i >= 0; i--) {
        const p = macroParticles[i];
        p.trail.push({ x: p.x, y: p.y });
        if (p.trail.length > 12) p.trail.shift();

        p.x += p.vx;
        p.y += p.vy;

        // Foil Interaction
        if (!p.deflected && p.x >= cx) {
          p.deflected = true;
          if (mode === 'rutherford') {
            const rand = Math.random();
            if (rand < 0.04) {
              // Rare wide deflection / backward bounce (>90 deg)
              const angle = Math.random() < 0.5 
                ? (Math.PI * 0.72 + Math.random() * 0.38) 
                : (-Math.PI * 0.72 - Math.random() * 0.38);
              const speed = 1.45;
              p.vx = Math.cos(angle) * speed;
              p.vy = Math.sin(angle) * speed;
            } else if (rand < 0.15) {
              // Moderate deflection (15° - 45°)
              const angle = (Math.random() < 0.5 ? 1 : -1) * (0.2 + Math.random() * 0.45);
              const speed = 1.45;
              p.vx = Math.cos(angle) * speed;
              p.vy = Math.sin(angle) * speed;
            } else {
              // Undeflected (slight jitter only)
              p.vy = (Math.random() - 0.5) * 0.12;
            }
          } else {
            // Thomson plum-pudding: virtually all pass undeflected
            p.vy = (Math.random() - 0.5) * 0.08;
          }
        }

        // Screen collision test
        const dx = p.x - cx;
        const dy = p.y - cy;
        const dist = Math.sqrt(dx * dx + dy * dy);

        let hit = false;
        const angleFromCenter = Math.atan2(dy, dx);
        const inApertureGap = (angleFromCenter > 0.75 * Math.PI || angleFromCenter < -0.75 * Math.PI);

        if (dist >= screenR) {
          if (!inApertureGap || p.x > cx) {
            hit = true;
          }
        }

        if (hit || p.x > w + 20 || p.x < -20 || p.y < -20 || p.y > h + 20) {
          if (hit) {
            flashes.push({
              x: cx + (dx / dist) * screenR,
              y: cy + (dy / dist) * screenR,
              life: 1.0,
              maxLife: 1.0
            });
          }
          macroParticles.splice(i, 1);
          continue;
        }

        // Draw particle trail (visible trajectory)
        if (p.trail.length > 1) {
          ctx.beginPath();
          ctx.moveTo(p.trail[0].x, p.trail[0].y);
          for (let t = 1; t < p.trail.length; t++) {
            ctx.lineTo(p.trail[t].x, p.trail[t].y);
          }
          ctx.strokeStyle = 'rgba(56, 189, 248, 0.45)';
          ctx.lineWidth = 1.8;
          ctx.stroke();
        }

        // Draw glowing particle head
        ctx.fillStyle = '#bae6fd';
        ctx.shadowColor = '#38bdf8';
        ctx.shadowBlur = 6;
        ctx.beginPath();
        ctx.arc(p.x, p.y, 2.2, 0, Math.PI * 2);
        ctx.fill();
        ctx.shadowBlur = 0;
      }

      // Draw Screen Flashes / Scintillations
      for (let i = flashes.length - 1; i >= 0; i--) {
        const f = flashes[i];
        const progress = 1.0 - f.life; // 0 to 1

        // Outer expanding flash ring
        ctx.beginPath();
        ctx.arc(f.x, f.y, 3 + progress * 7, 0, Math.PI * 2);
        ctx.strokeStyle = `rgba(74, 222, 128, ${f.life * 0.7})`;
        ctx.lineWidth = 1.5;
        ctx.stroke();

        // Bright central scintillation flash
        ctx.fillStyle = `rgba(220, 252, 231, ${f.life})`;
        ctx.shadowColor = '#4ade80';
        ctx.shadowBlur = 8;
        ctx.beginPath();
        ctx.arc(f.x, f.y, 2.8 * f.life, 0, Math.PI * 2);
        ctx.fill();
        ctx.shadowBlur = 0;

        f.life -= 0.025; // Lasts ~40 frames (~650ms), clearly visible
        if (f.life <= 0) flashes.splice(i, 1);
      }
    }

    // --- MICRO SIMULATION ---
    let microParticles = [];
    let microSpawnTimer = 0;

    function updateMicro(ctx, w, h) {
      ctx.clearRect(0, 0, w, h);

      // Define grid of atoms
      const rows = 3;
      const cols = 2;
      const nuclei = [];
      const startX = w * 0.42;
      const startY = h * 0.22;
      const spacingY = h * 0.32;
      const spacingX = w * 0.34;

      for (let c = 0; c < cols; c++) {
        for (let r = 0; r < rows; r++) {
          nuclei.push({
            x: startX + c * spacingX,
            y: startY + r * spacingY + (c % 2 ? spacingY * 0.5 : 0)
          });
        }
      }

      // Draw Atoms
      nuclei.forEach(n => {
        if (mode === 'thomson') {
          // Plum pudding: diffuse positive cloud
          const grad = ctx.createRadialGradient(n.x, n.y, 2, n.x, n.y, spacingY * 0.46);
          grad.addColorStop(0, 'rgba(239, 68, 68, 0.35)');
          grad.addColorStop(0.7, 'rgba(239, 68, 68, 0.15)');
          grad.addColorStop(1, 'rgba(239, 68, 68, 0)');
          ctx.fillStyle = grad;
          ctx.beginPath();
          ctx.arc(n.x, n.y, spacingY * 0.46, 0, Math.PI * 2);
          ctx.fill();

          // Electrons (- dots embedded)
          ctx.fillStyle = '#38bdf8';
          for (let a = 0; a < 6; a++) {
            const angle = a * (Math.PI / 3) + 0.3;
            const dist = spacingY * 0.24;
            const ex = n.x + Math.cos(angle) * dist;
            const ey = n.y + Math.sin(angle) * dist;
            ctx.beginPath();
            ctx.arc(ex, ey, 2.5, 0, Math.PI * 2);
            ctx.fill();

            // Minus sign
            ctx.fillStyle = '#ffffff';
            ctx.fillRect(ex - 1.5, ey - 0.5, 3, 1);
            ctx.fillStyle = '#38bdf8';
          }
        } else {
          // Rutherford: Vast empty space + tiny positive nucleus
          // Electron cloud boundary (dashed)
          ctx.strokeStyle = 'rgba(148, 163, 184, 0.18)';
          ctx.lineWidth = 1;
          ctx.setLineDash([3, 4]);
          ctx.beginPath();
          ctx.arc(n.x, n.y, spacingY * 0.46, 0, Math.PI * 2);
          ctx.stroke();
          ctx.setLineDash([]);

          // Nucleus glow
          const nucGlow = ctx.createRadialGradient(n.x, n.y, 2, n.x, n.y, 14);
          nucGlow.addColorStop(0, 'rgba(239, 68, 68, 0.6)');
          nucGlow.addColorStop(1, 'rgba(239, 68, 68, 0)');
          ctx.fillStyle = nucGlow;
          ctx.beginPath();
          ctx.arc(n.x, n.y, 14, 0, Math.PI * 2);
          ctx.fill();

          // Dense positive nucleus (+ charge)
          ctx.fillStyle = '#ef4444';
          ctx.beginPath();
          ctx.arc(n.x, n.y, 4.5, 0, Math.PI * 2);
          ctx.fill();

          // Plus sign
          ctx.fillStyle = '#ffffff';
          ctx.fillRect(n.x - 2, n.y - 0.6, 4, 1.2);
          ctx.fillRect(n.x - 0.6, n.y - 2, 1.2, 4);
        }
      });

      // Spawn Micro Alpha Particles
      microSpawnTimer++;
      if (microSpawnTimer % 14 === 0) {
        // Aim some directly toward nuclei and others through gaps to demonstrate both effects
        let targetY;
        const choice = Math.random();
        if (choice < 0.25) {
          // Direct hit aiming near first column nucleus
          targetY = nuclei[1].y + (Math.random() - 0.5) * 8;
        } else if (choice < 0.5) {
          // Near miss aiming near another nucleus
          targetY = nuclei[0].y + (Math.random() < 0.5 ? 1 : -1) * (14 + Math.random() * 10);
        } else {
          // Pass through empty space
          targetY = Math.random() * h;
        }

        microParticles.push({
          x: 0,
          y: targetY,
          vx: 1.5, // Slowed down so traversal is comfortably trackable (>1.5s)
          vy: 0,
          trail: []
        });
      }

      // Update & Draw Micro Particles
      for (let i = microParticles.length - 1; i >= 0; i--) {
        const p = microParticles[i];
        p.trail.push({ x: p.x, y: p.y });
        if (p.trail.length > 20) p.trail.shift();

        if (mode === 'rutherford') {
          // Coulomb repulsion: F = k / r^2
          nuclei.forEach(n => {
            const dx = p.x - n.x;
            const dy = p.y - n.y;
            const distSq = dx * dx + dy * dy;
            const dist = Math.sqrt(distSq);

            if (dist < 65) {
              const force = 160 / (distSq + 25);
              p.vx += (dx / dist) * force;
              p.vy += (dy / dist) * force;
            }
          });
        } else {
          // Thomson: continuous diffuse charge results in no concentrated force
          p.vy += (Math.random() - 0.5) * 0.02;
        }

        p.x += p.vx;
        p.y += p.vy;

        // Draw particle trail
        if (p.trail.length > 1) {
          ctx.beginPath();
          ctx.moveTo(p.trail[0].x, p.trail[0].y);
          for (let t = 1; t < p.trail.length; t++) {
            ctx.lineTo(p.trail[t].x, p.trail[t].y);
          }
          ctx.strokeStyle = 'rgba(56, 189, 248, 0.55)';
          ctx.lineWidth = 2;
          ctx.stroke();
        }

        // Draw particle head
        ctx.fillStyle = '#38bdf8';
        ctx.shadowColor = '#0284c7';
        ctx.shadowBlur = 5;
        ctx.beginPath();
        ctx.arc(p.x, p.y, 3, 0, Math.PI * 2);
        ctx.fill();
        ctx.shadowBlur = 0;

        // Out of bounds removal
        if (p.x > w + 40 || p.x < -40 || p.y < -40 || p.y > h + 40) {
          microParticles.splice(i, 1);
        }
      }
    }

    function animate() {
      const dpr = window.devicePixelRatio || 1;
      const mw = macroCanvas.width / dpr;
      const mh = macroCanvas.height / dpr;
      const uw = microCanvas.width / dpr;
      const uh = microCanvas.height / dpr;

      macroCtx.save();
      macroCtx.scale(dpr, dpr);
      updateMacro(macroCtx, mw, mh);
      macroCtx.restore();

      microCtx.save();
      microCtx.scale(dpr, dpr);
      updateMicro(microCtx, uw, uh);
      microCtx.restore();

      requestAnimationFrame(animate);
    }

    animate();
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="1:1">
  <title>Bohr Model & Emission Spectrum</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      width: 100%;
      min-height: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      padding: 10px;
      user-select: none;
    }

    .header {
      text-align: center;
      margin-bottom: 6px;
    }

    .title {
      font-size: 16px;
      font-weight: 700;
      color: #0f172a;
    }

    .subtitle {
      font-size: 12px;
      color: #64748b;
      margin-top: 1px;
    }

    /* Atom Visual Canvas Container */
    .atom-stage {
      width: 100%;
      max-width: 440px;
      height: 200px;
      position: relative;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      overflow: hidden;
    }

    .atom-svg {
      width: 100%;
      height: 100%;
      display: block;
    }

    /* Spectrometer Section */
    .spectrum-container {
      width: 100%;
      max-width: 440px;
      margin-top: 8px;
      display: flex;
      flex-direction: column;
      gap: 3px;
    }

    .spectrum-bar-wrap {
      position: relative;
      width: 100%;
      height: 38px;
      background: #090d16;
      border-radius: 6px;
      overflow: hidden;
      box-shadow: inset 0 2px 4px rgba(0,0,0,0.5);
    }

    .spectral-line {
      position: absolute;
      top: 0;
      bottom: 0;
      width: 4px;
      transform: translateX(-50%);
      cursor: pointer;
      opacity: 0.75;
      transition: opacity 0.25s, filter 0.25s, width 0.25s;
    }

    .spectral-line:hover, .spectral-line.active {
      opacity: 1;
      width: 5px;
      filter: drop-shadow(0 0 6px currentColor);
      z-index: 2;
    }

    .spectrum-labels {
      display: flex;
      justify-content: space-between;
      font-size: 11px;
      font-weight: 600;
      color: #64748b;
      padding: 0 4px;
    }

    /* Info Readout Card */
    .readout-card {
      width: 100%;
      max-width: 440px;
      margin-top: 8px;
      background: #f1f5f9;
      border-radius: 8px;
      padding: 6px 12px;
      display: flex;
      justify-content: space-around;
      align-items: center;
      border: 1px solid #e2e8f0;
    }

    .readout-item {
      display: flex;
      flex-direction: column;
      align-items: center;
    }

    .readout-label {
      font-size: 10px;
      text-transform: uppercase;
      font-weight: 700;
      color: #64748b;
      letter-spacing: 0.5px;
    }

    .readout-val {
      font-size: 14px;
      font-weight: 700;
      color: #0f172a;
      font-feature-settings: "tnum";
    }

    /* Transition Buttons */
    .controls-grid {
      width: 100%;
      max-width: 440px;
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 6px;
      margin-top: 8px;
    }

    .btn-transition {
      background: #ffffff;
      border: 2px solid #e2e8f0;
      border-radius: 8px;
      padding: 6px 2px;
      font-size: 12px;
      font-weight: 700;
      color: #334155;
      cursor: pointer;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 2px;
      box-shadow: 0 1px 2px rgba(0,0,0,0.04);
      transition: background-color 0.2s, border-color 0.2s, box-shadow 0.2s, color 0.2s;
    }

    .btn-transition .wl-sub {
      font-size: 10px;
      font-weight: 600;
      color: #64748b;
    }

    .btn-transition.active {
      background: #ffffff;
      color: #0f172a;
      box-shadow: 0 2px 8px rgba(0,0,0,0.1);
    }

    .btn-transition[data-id="0"].active { border-color: #ef4444; }
    .btn-transition[data-id="1"].active { border-color: #06b6d4; }
    .btn-transition[data-id="2"].active { border-color: #3b82f6; }
    .btn-transition[data-id="3"].active { border-color: #8b5cf6; }

    .btn-transition[data-id="0"]:hover { border-color: #fca5a5; }
    .btn-transition[data-id="1"]:hover { border-color: #a5f3fc; }
    .btn-transition[data-id="2"]:hover { border-color: #bfdbfe; }
    .btn-transition[data-id="3"]:hover { border-color: #ddd6fe; }

    /* SVG Elements */
    .orbit {
      fill: none;
      stroke: #cbd5e1;
      stroke-width: 1.2;
      stroke-dasharray: 3 3;
    }

    .orbit-target {
      stroke: #0284c7;
      stroke-width: 2;
      stroke-dasharray: none;
      opacity: 0.85;
    }

    .orbit-label {
      font-size: 9px;
      font-weight: 700;
      fill: #94a3b8;
    }

    .orbit-label.target {
      fill: #0284c7;
    }

    .photon-wave {
      fill: none;
      stroke-width: 2.5;
      stroke-linecap: round;
      opacity: 0;
    }

    .photon-tag {
      font-size: 11px;
      font-weight: 700;
      opacity: 0;
    }
  </style>
</head>
<body>

  <div class="header">
    <div class="title">Bohr Model & Emission Spectrum</div>
    <div class="subtitle">Transitions to shell n=2 emit visible light (Balmer Series)</div>
  </div>

  
  <div class="atom-stage">
    <svg class="atom-svg" viewBox="0 0 400 200" id="atomSvg">
      <defs>
        <radialGradient id="nucGrad" cx="40%" cy="40%" r="60%">
          <stop offset="0%" stop-color="#f87171" />
          <stop offset="100%" stop-color="#dc2626" />
        </radialGradient>
        <filter id="glow" x="-20%" y="-20%" width="140%" height="140%">
          <feGaussianBlur stdDeviation="2" result="blur" />
          <feComposite in="SourceGraphic" in2="blur" operator="over" />
        </filter>
      </defs>

      
      
      <circle class="orbit" cx="145" cy="100" r="18" />
      <circle class="orbit orbit-target" cx="145" cy="100" r="34" />
      <circle class="orbit" cx="145" cy="100" r="52" />
      <circle class="orbit" cx="145" cy="100" r="70" />
      <circle class="orbit" cx="145" cy="100" r="88" />
      <circle class="orbit" cx="145" cy="100" r="106" />

      
      <text class="orbit-label" x="145" y="79">n=1</text>
      <text class="orbit-label target" x="145" y="63">n=2 (Balmer)</text>
      <text class="orbit-label" x="145" y="45">n=3</text>
      <text class="orbit-label" x="145" y="27">n=4</text>
      <text class="orbit-label" x="145" y="9">n=5</text>
      <text class="orbit-label" x="145" y="-9">n=6</text>

      
      <circle cx="145" cy="100" r="10" fill="url(#nucGrad)" />
      <text x="145" y="103.5" text-anchor="middle" font-size="11" font-weight="bold" fill="#ffffff">+</text>

      
      <path id="photonWave" class="photon-wave" d="" />
      <text id="photonLabel" class="photon-tag" x="320" y="75" text-anchor="middle"></text>

      
      <circle id="electron" cx="197" cy="100" r="5.5" fill="#0284c7" stroke="#ffffff" stroke-width="1.5" filter="url(#glow)" />
    </svg>
  </div>

  
  <div class="spectrum-container">
    <div class="spectrum-bar-wrap" id="spectrumBar">
      
      
      <div class="spectral-line" data-id="3" style="left: 9.38%; background-color: #8b5cf6; color: #8b5cf6;" title="n=6→2 (410 nm)"></div>
      
      <div class="spectral-line" data-id="2" style="left: 16.88%; background-color: #3b82f6; color: #3b82f6;" title="n=5→2 (434 nm)"></div>
      
      <div class="spectral-line" data-id="1" style="left: 33.13%; background-color: #06b6d4; color: #06b6d4;" title="n=4→2 (486 nm)"></div>
      
      <div class="spectral-line" data-id="0" style="left: 86.25%; background-color: #ef4444; color: #ef4444;" title="n=3→2 (656 nm)"></div>
    </div>
    <div class="spectrum-labels">
      <span>400 nm (UV/Violet)</span>
      <span>500 nm</span>
      <span>600 nm</span>
      <span>700 nm (Red)</span>
    </div>
  </div>

  
  <div class="readout-card">
    <div class="readout-item">
      <span class="readout-label">Transition</span>
      <span class="readout-val" id="valTrans">n=3 → n=2</span>
    </div>
    <div class="readout-item">
      <span class="readout-label">Energy (&Delta;E)</span>
      <span class="readout-val" id="valEnergy">1.89 eV</span>
    </div>
    <div class="readout-item">
      <span class="readout-label">Wavelength</span>
      <span class="readout-val" id="valWl" style="color: #dc2626;">656 nm</span>
    </div>
  </div>

  
  <div class="controls-grid">
    <button class="btn-transition active" data-id="0">
      <span>3 &rarr; 2</span>
      <span class="wl-sub">656 nm</span>
    </button>
    <button class="btn-transition" data-id="1">
      <span>4 &rarr; 2</span>
      <span class="wl-sub">486 nm</span>
    </button>
    <button class="btn-transition" data-id="2">
      <span>5 &rarr; 2</span>
      <span class="wl-sub">434 nm</span>
    </button>
    <button class="btn-transition" data-id="3">
      <span>6 &rarr; 2</span>
      <span class="wl-sub">410 nm</span>
    </button>
  </div>

  <script>
    const transitions = [
      { ni: 3, r_start: 52, wl: 656, energy: '1.89 eV', color: '#ef4444', textCol: '#dc2626', freqFactor: 3 },
      { ni: 4, r_start: 70, wl: 486, energy: '2.55 eV', color: '#06b6d4', textCol: '#0891b2', freqFactor: 4.5 },
      { ni: 5, r_start: 88, wl: 434, energy: '2.86 eV', color: '#3b82f6', textCol: '#2563eb', freqFactor: 6 },
      { ni: 6, r_start: 106, wl: 410, energy: '3.02 eV', color: '#8b5cf6', textCol: '#7c3aed', freqFactor: 7.5 }
    ];

    const cx = 145;
    const cy = 100;
    const r_target = 34; // n=2 shell radius

    let activeIndex = 0;
    let animTimer = null;

    const electron = document.getElementById('electron');
    const photonWave = document.getElementById('photonWave');
    const photonLabel = document.getElementById('photonLabel');
    const valTrans = document.getElementById('valTrans');
    const valEnergy = document.getElementById('valEnergy');
    const valWl = document.getElementById('valWl');
    const buttons = document.querySelectorAll('.btn-transition');
    const lines = document.querySelectorAll('.spectral-line');

    function createWavePath(startX, startY, endX, waves, amplitude) {
      const length = endX - startX;
      let d = `M ${startX} ${startY}`;
      const points = 40;
      for (let i = 1; i <= points; i++) {
        const t = i / points;
        const x = startX + t * length;
        const y = startY + Math.sin(t * Math.PI * 2 * waves) * amplitude;
        d += ` L ${x.toFixed(1)} ${y.toFixed(1)}`;
      }
      return d;
    }

    function triggerTransition(idx) {
      activeIndex = idx;
      const data = transitions[idx];

      // Update UI selection
      buttons.forEach((b, i) => b.classList.toggle('active', i === idx));
      lines.forEach((l, i) => l.classList.toggle('active', i === idx));

      // Update Readouts
      valTrans.textContent = `n=${data.ni} → n=2`;
      valEnergy.textContent = data.energy;
      valWl.textContent = `${data.wl} nm`;
      valWl.style.color = data.textCol;

      // Reset active animation state
      if (animTimer) cancelAnimationFrame(animTimer);
      photonWave.style.opacity = '0';
      photonLabel.style.opacity = '0';

      // Animation: Step 1 - Place electron at initial orbit
      const startX = cx + data.r_start;
      const targetX = cx + r_target;
      electron.setAttribute('cx', startX);
      electron.setAttribute('cy', cy);

      // Animate Electron inward smoothly
      const startTime = performance.now();
      const dropDuration = 450; // ms

      function animateDrop(now) {
        const elapsed = now - startTime;
        const progress = Math.min(1, elapsed / dropDuration);
        // ease-in-out cubic
        const ease = progress < 0.5 
          ? 4 * progress * progress * progress 
          : 1 - Math.pow(-2 * progress + 2, 3) / 2;

        const currentX = startX - (startX - targetX) * ease;
        electron.setAttribute('cx', currentX);

        if (progress < 1) {
          animTimer = requestAnimationFrame(animateDrop);
        } else {
          // Electron reached n=2 target, fire photon
          firePhoton(data);
        }
      }

      animTimer = requestAnimationFrame(animateDrop);
    }

    function firePhoton(data) {
      const photonStartX = cx + r_target;
      const photonEndX = 375;
      const wavePathD = createWavePath(photonStartX, cy, photonEndX, data.freqFactor, 8);

      photonWave.setAttribute('d', wavePathD);
      photonWave.setAttribute('stroke', data.color);
      photonWave.style.opacity = '1';
      photonWave.style.transition = 'opacity 0.2s ease-in';

      photonLabel.textContent = `hf (${data.wl} nm)`;
      photonLabel.setAttribute('x', (photonStartX + photonEndX) / 2 + 10);
      photonLabel.setAttribute('y', cy - 14);
      photonLabel.setAttribute('fill', data.textCol);
      photonLabel.style.opacity = '1';
      photonLabel.style.transition = 'opacity 0.3s ease-in';
    }

    // Button click handlers
    buttons.forEach((btn) => {
      btn.addEventListener('click', () => {
        const id = parseInt(btn.getAttribute('data-id'), 10);
        triggerTransition(id);
      });
    });

    // Spectrometer line click handlers
    lines.forEach((line) => {
      line.addEventListener('click', () => {
        const id = parseInt(line.getAttribute('data-id'), 10);
        triggerTransition(id);
      });
    });

    // Initial state on load
    triggerTransition(0);
  </script>
</body>
</html>

<!DOCTYPE html>
<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>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px;
      user-select: none;
    }

    /* Timeline Stepper */
    .timeline {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 6px;
      width: 100%;
      max-width: 540px;
      margin-bottom: 8px;
    }

    .timeline-btn {
      background: #f1f5f9;
      border: 2px solid transparent;
      border-radius: 8px;
      padding: 6px 4px;
      text-align: center;
      cursor: pointer;
      transition: background 0.2s, border-color 0.2s;
    }

    .timeline-btn:hover {
      background: #e2e8f0;
    }

    .timeline-btn.active {
      background: #eff6ff;
      border-color: #2563eb;
    }

    .timeline-year {
      font-size: 11px;
      font-weight: 700;
      color: #64748b;
      display: block;
    }

    .timeline-btn.active .timeline-year {
      color: #2563eb;
    }

    .timeline-name {
      font-size: 13px;
      font-weight: 700;
      color: #1e2945;
      display: block;
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }

    /* Visual Stage */
    .stage-container {
      position: relative;
      width: 100%;
      max-width: 540px;
      height: 220px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      display: flex;
      align-items: center;
      justify-content: center;
      overflow: hidden;
    }

    .model-view {
      position: absolute;
      inset: 0;
      display: flex;
      align-items: center;
      justify-content: center;
      opacity: 0;
      pointer-events: none;
      transition: opacity 0.3s ease;
    }

    .model-view.active {
      opacity: 1;
      pointer-events: auto;
    }

    svg {
      width: 100%;
      height: 100%;
      max-height: 210px;
    }

    /* Info Badges (Evidence & Flaw) */
    .meta-container {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 8px;
      width: 100%;
      max-width: 540px;
      margin-top: 8px;
    }

    .meta-card {
      padding: 8px 12px;
      border-radius: 8px;
      font-size: 12px;
      line-height: 1.3;
      display: flex;
      flex-direction: column;
      gap: 2px;
    }

    .meta-evidence {
      background: #f0fdf4;
      border: 1px solid #bbf7d0;
      color: #166534;
    }

    .meta-flaw {
      background: #fef2f2;
      border: 1px solid #fecaca;
      color: #991b1b;
    }

    .meta-label {
      font-size: 10px;
      font-weight: 800;
      letter-spacing: 0.5px;
      text-transform: uppercase;
      opacity: 0.8;
    }

    .meta-val {
      font-weight: 600;
      font-size: 13px;
    }

    /* Controls */
    .controls {
      display: flex;
      align-items: center;
      gap: 8px;
      margin-top: 6px;
    }

    .ctrl-btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      color: #334155;
      padding: 4px 12px;
      border-radius: 6px;
      font-size: 12px;
      font-weight: 600;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
    }

    .ctrl-btn:hover {
      background: #f1f5f9;
    }

    /* Animations */
    @keyframes spinOrbit {
      from { transform: rotate(0deg); }
      to { transform: rotate(360deg); }
    }

    @keyframes photonPulse {
      0%, 100% { opacity: 0.2; stroke-dashoffset: 0; }
      50% { opacity: 1; stroke-dashoffset: 20; }
    }

    .orbit-1 { transform-origin: 150px 105px; animation: spinOrbit 4s linear infinite; }
    .orbit-2 { transform-origin: 150px 105px; animation: spinOrbit 6s linear infinite reverse; }
    .orbit-3 { transform-origin: 150px 105px; animation: spinOrbit 9s linear infinite; }
    .photon-wave { stroke-dasharray: 4, 4; animation: photonPulse 2s ease-in-out infinite; }
  </style>
</head>
<body>

  
  <div class="timeline" role="tablist">
    <button class="timeline-btn active" onclick="setModel(0)" role="tab" id="tab-0">
      <span class="timeline-year">1803</span>
      <span class="timeline-name">Dalton</span>
    </button>
    <button class="timeline-btn" onclick="setModel(1)" role="tab" id="tab-1">
      <span class="timeline-year">1897</span>
      <span class="timeline-name">Thomson</span>
    </button>
    <button class="timeline-btn" onclick="setModel(2)" role="tab" id="tab-2">
      <span class="timeline-year">1909</span>
      <span class="timeline-name">Rutherford</span>
    </button>
    <button class="timeline-btn" onclick="setModel(3)" role="tab" id="tab-3">
      <span class="timeline-year">1913</span>
      <span class="timeline-name">Bohr</span>
    </button>
  </div>

  
  <div class="stage-container">
    
    
    <div class="model-view active" id="view-0">
      <svg viewBox="0 0 300 210">
        <defs>
          <radialGradient id="daltonGrad" cx="35%" cy="35%" r="65%">
            <stop offset="0%" stop-color="#93c5fd" />
            <stop offset="45%" stop-color="#3b82f6" />
            <stop offset="100%" stop-color="#1d4ed8" />
          </radialGradient>
        </defs>
        <circle cx="150" cy="105" r="70" fill="url(#daltonGrad)" stroke="#1e40af" stroke-width="2" />
        <text x="150" y="110" fill="#ffffff" font-size="14" font-weight="700" text-anchor="middle">Solid &amp; Indivisible</text>
        <text x="150" y="195" fill="#64748b" font-size="12" font-weight="600" text-anchor="middle">Uniform billiard ball</text>
      </svg>
    </div>

    
    <div class="model-view" id="view-1">
      <svg viewBox="0 0 300 210">
        
        <circle cx="150" cy="105" r="70" fill="#fee2e2" stroke="#ef4444" stroke-width="2" stroke-dasharray="4,2" />
        <text x="150" y="55" fill="#b91c1c" font-size="13" font-weight="700" text-anchor="middle">+ Positive Sphere</text>
        
        
        <g transform="translate(115, 85)">
          <circle cx="0" cy="0" r="10" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
          <text x="0" y="4" fill="#fff" font-size="13" font-weight="800" text-anchor="middle">−</text>
        </g>
        <g transform="translate(170, 80)">
          <circle cx="0" cy="0" r="10" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
          <text x="0" y="4" fill="#fff" font-size="13" font-weight="800" text-anchor="middle">−</text>
        </g>
        <g transform="translate(135, 120)">
          <circle cx="0" cy="0" r="10" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
          <text x="0" y="4" fill="#fff" font-size="13" font-weight="800" text-anchor="middle">−</text>
        </g>
        <g transform="translate(175, 130)">
          <circle cx="0" cy="0" r="10" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
          <text x="0" y="4" fill="#fff" font-size="13" font-weight="800" text-anchor="middle">−</text>
        </g>
        <text x="150" y="195" fill="#64748b" font-size="12" font-weight="600" text-anchor="middle">Electrons in positive gel</text>
      </svg>
    </div>

    
    <div class="model-view" id="view-2">
      <svg viewBox="0 0 300 210">
        
        <ellipse cx="150" cy="105" rx="80" ry="26" fill="none" stroke="#cbd5e1" stroke-width="1.5" transform="rotate(30 150 105)" />
        <ellipse cx="150" cy="105" rx="80" ry="26" fill="none" stroke="#cbd5e1" stroke-width="1.5" transform="rotate(-30 150 105)" />
        <ellipse cx="150" cy="105" rx="80" ry="26" fill="none" stroke="#cbd5e1" stroke-width="1.5" transform="rotate(90 150 105)" />

        
        <g class="orbit-1">
          <circle cx="220" cy="105" r="5" fill="#3b82f6" />
        </g>
        <g class="orbit-2">
          <circle cx="80" cy="105" r="5" fill="#3b82f6" />
        </g>

        
        <circle cx="150" cy="105" r="14" fill="#ef4444" stroke="#b91c1c" stroke-width="2" />
        <text x="150" y="109" fill="#ffffff" font-size="11" font-weight="800" text-anchor="middle">+</text>
        
        <text x="150" y="24" fill="#b91c1c" font-size="12" font-weight="700" text-anchor="middle">Dense (+) Nucleus</text>
        <text x="150" y="195" fill="#64748b" font-size="12" font-weight="600" text-anchor="middle">Mostly empty space</text>
      </svg>
    </div>

    
    <div class="model-view" id="view-3">
      <svg viewBox="0 0 300 210">
        
        <circle cx="150" cy="105" r="32" fill="none" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="3,3" />
        <circle cx="150" cy="105" r="56" fill="none" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="3,3" />
        <circle cx="150" cy="105" r="78" fill="none" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="3,3" />

        
        <text x="186" y="100" fill="#64748b" font-size="10" font-weight="700">n=1</text>
        <text x="210" y="100" fill="#64748b" font-size="10" font-weight="700">n=2</text>
        <text x="232" y="100" fill="#64748b" font-size="10" font-weight="700">n=3</text>

        
        <circle cx="150" cy="105" r="12" fill="#ef4444" stroke="#b91c1c" stroke-width="2" />
        <text x="150" y="109" fill="#ffffff" font-size="11" font-weight="800" text-anchor="middle">+</text>

        
        <g class="orbit-1">
          <circle cx="182" cy="105" r="5" fill="#3b82f6" />
        </g>
        <g class="orbit-2">
          <circle cx="94" cy="105" r="5" fill="#3b82f6" />
        </g>

        
        <path d="M 175,90 Q 185,75 195,90 T 215,90" fill="none" stroke="#f59e0b" stroke-width="2.5" class="photon-wave" />
        <text x="220" y="78" fill="#d97706" font-size="11" font-weight="800">Photon (hν)</text>
        <text x="150" y="195" fill="#64748b" font-size="12" font-weight="600" text-anchor="middle">Fixed energy levels</text>
      </svg>
    </div>

  </div>

  
  <div class="meta-container">
    <div class="meta-card meta-evidence">
      <span class="meta-label">Key Evidence ✓</span>
      <span class="meta-val" id="evidence-text">Definite Proportions</span>
    </div>
    <div class="meta-card meta-flaw">
      <span class="meta-label">Model Flaw ✗</span>
      <span class="meta-val" id="flaw-text">Ignores subatomic parts</span>
    </div>
  </div>

  
  <div class="controls">
    <button class="ctrl-btn" onclick="prevModel()">◀ Prev</button>
    <button class="ctrl-btn" id="playBtn" onclick="toggleAuto()">▶ Auto-Play</button>
    <button class="ctrl-btn" onclick="nextModel()">Next ▶</button>
  </div>

  <script>
    const models = [
      {
        year: '1803',
        name: 'Dalton',
        evidence: 'Definite Proportions',
        flaw: 'Ignores subatomic parts'
      },
      {
        year: '1897',
        name: 'Thomson',
        evidence: 'Cathode Ray deflection',
        flaw: 'No central nucleus'
      },
      {
        year: '1909',
        name: 'Rutherford',
        evidence: 'Gold Foil back-scattering',
        flaw: 'Orbital electron collapse'
      },
      {
        year: '1913',
        name: 'Bohr',
        evidence: 'Emission line spectra',
        flaw: 'Fails for complex atoms'
      }
    ];

    let currentIdx = 0;
    let timer = null;

    function setModel(idx) {
      currentIdx = (idx + models.length) % models.length;

      // Update timeline tabs
      for (let i = 0; i < models.length; i++) {
        const tab = document.getElementById('tab-' + i);
        const view = document.getElementById('view-' + i);
        if (i === currentIdx) {
          tab.classList.add('active');
          view.classList.add('active');
        } else {
          tab.classList.remove('active');
          view.classList.remove('active');
        }
      }

      // Update text
      document.getElementById('evidence-text').textContent = models[currentIdx].evidence;
      document.getElementById('flaw-text').textContent = models[currentIdx].flaw;
    }

    function nextModel() {
      setModel(currentIdx + 1);
    }

    function prevModel() {
      setModel(currentIdx - 1);
    }

    function toggleAuto() {
      const btn = document.getElementById('playBtn');
      if (timer) {
        clearInterval(timer);
        timer = null;
        btn.textContent = '▶ Auto-Play';
      } else {
        nextModel();
        timer = setInterval(nextModel, 3500);
        btn.textContent = '⏸ Pause';
      }
    }
  </script>
</body>
</html>

<!DOCTYPE html>
<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">
  <title>Dalton's Model & Definite Proportions</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      user-select: none;
    }

    body {
      background: #f8f9fa;
      color: #1e2945;
      font-family: system-ui, -apple-system, sans-serif;
      padding: 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      width: 100%;
    }

    .controls {
      display: flex;
      gap: 8px;
      justify-content: center;
      margin-bottom: 12px;
    }

    .btn {
      background: #ffffff;
      border: 1.5px solid #cbd5e1;
      border-radius: 8px;
      padding: 6px 16px;
      font-size: 14px;
      font-weight: 700;
      color: #1e2945;
      cursor: pointer;
      box-shadow: 0 1px 2px rgba(0,0,0,0.05);
      transition: background-color 0.2s, border-color 0.2s, color 0.2s;
    }

    .btn.active {
      background: #2563eb;
      border-color: #2563eb;
      color: #ffffff;
    }

    .reaction-area {
      display: flex;
      align-items: center;
      justify-content: space-around;
      width: 100%;
      max-width: 620px;
      flex: 1;
      gap: 6px;
    }

    .component-box {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px 8px;
      flex: 1;
      min-height: 175px;
      box-shadow: 0 2px 4px rgba(0,0,0,0.03);
    }

    .symbol-label {
      font-size: 14px;
      font-weight: 700;
      margin-bottom: 8px;
      color: #1e2945;
    }

    .spheres-container {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 8px;
      min-height: 80px;
      width: 100%;
    }

    .ball-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 4px;
    }

    /* Billiard Ball Spheres */
    .ball-h {
      width: 20px;
      height: 20px;
      border-radius: 50%;
      background: radial-gradient(circle at 35% 35%, #93c5fd, #2563eb 70%, #1e40af);
      box-shadow: 1px 2px 4px rgba(0,0,0,0.25);
    }

    .ball-o {
      width: 38px;
      height: 38px;
      border-radius: 50%;
      background: radial-gradient(circle at 35% 35%, #fca5a5, #dc2626 70%, #991b1b);
      box-shadow: 1px 3px 5px rgba(0,0,0,0.25);
    }

    .molecule-water {
      display: inline-flex;
      align-items: center;
      position: relative;
      height: 40px;
      padding: 0 6px;
    }

    .molecule-water .ball-o {
      position: relative;
      z-index: 1;
    }

    .molecule-water .ball-h.h-left {
      margin-right: -8px;
      z-index: 2;
      transform: translateY(6px);
    }

    .molecule-water .ball-h.h-right {
      margin-left: -8px;
      z-index: 2;
      transform: translateY(6px);
    }

    .mass-tag {
      margin-top: 10px;
      font-size: 15px;
      font-weight: 800;
      color: #0f172a;
      background: #f1f5f9;
      padding: 2px 10px;
      border-radius: 6px;
    }

    .operator {
      font-size: 22px;
      font-weight: 900;
      color: #64748b;
    }

    .ratio-bar {
      display: flex;
      align-items: center;
      justify-content: center;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 8px 16px;
      margin-top: 12px;
      width: 100%;
      max-width: 620px;
      font-size: 15px;
      font-weight: 700;
      color: #1e2945;
      gap: 12px;
      box-shadow: 0 1px 3px rgba(0,0,0,0.03);
    }

    .ratio-highlight {
      color: #2563eb;
      font-size: 16px;
      font-weight: 800;
      background: #eff6ff;
      padding: 2px 8px;
      border-radius: 4px;
    }
  </style>
</head>
<body>

  <div class="controls">
    <button class="btn active" id="btn1" onclick="setRatio(1)">1×</button>
    <button class="btn" id="btn2" onclick="setRatio(2)">2×</button>
    <button class="btn" id="btn3" onclick="setRatio(3)">3×</button>
  </div>

  <div class="reaction-area">
    
    <div class="component-box">
      <div class="symbol-label">Hydrogen</div>
      <div class="spheres-container" id="hContainer"></div>
      <div class="mass-tag" id="hMass">2 g</div>
    </div>

    <div class="operator">+</div>

    
    <div class="component-box">
      <div class="symbol-label">Oxygen</div>
      <div class="spheres-container" id="oContainer"></div>
      <div class="mass-tag" id="oMass">16 g</div>
    </div>

    <div class="operator">→</div>

    
    <div class="component-box">
      <div class="symbol-label">Water</div>
      <div class="spheres-container" id="wContainer"></div>
      <div class="mass-tag" id="wMass">18 g</div>
    </div>
  </div>

  <div class="ratio-bar">
    <span>Mass Ratio (H : O)</span>
    <span class="ratio-highlight" id="ratioText">2g : 16g = 1 : 8</span>
  </div>

  <script>
    function setRatio(multiplier) {
      document.querySelectorAll('.btn').forEach(btn => btn.classList.remove('active'));
      const activeBtn = document.getElementById('btn' + multiplier);
      if (activeBtn) activeBtn.classList.add('active');

      const hBox = document.getElementById('hContainer');
      const oBox = document.getElementById('oContainer');
      const wBox = document.getElementById('wContainer');

      let hHTML = '';
      let oHTML = '';
      let wHTML = '';

      for (let i = 0; i < multiplier; i++) {
        hHTML += '<div class="ball-row"><div class="ball-h"></div><div class="ball-h"></div></div>';
        oHTML += '<div class="ball-row"><div class="ball-o"></div></div>';
        wHTML += '<div class="molecule-water"><div class="ball-h h-left"></div><div class="ball-o"></div><div class="ball-h h-right"></div></div>';
      }

      hBox.innerHTML = hHTML;
      oBox.innerHTML = oHTML;
      wBox.innerHTML = wHTML;

      const hTotal = 2 * multiplier;
      const oTotal = 16 * multiplier;
      const wTotal = 18 * multiplier;

      document.getElementById('hMass').textContent = hTotal + ' g';
      document.getElementById('oMass').textContent = oTotal + ' g';
      document.getElementById('wMass').textContent = wTotal + ' g';

      document.getElementById('ratioText').textContent = hTotal + 'g : ' + oTotal + 'g = 1 : 8';
    }

    setRatio(1);
  </script>
</body>
</html>

OGS.11.PS.AT.1

Aligned learning resources

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