{"id":4520,"date":"2026-05-28T06:05:16","date_gmt":"2026-05-28T05:05:16","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/predicting-diatomic-mass-spectra\/"},"modified":"2026-10-14T09:05:21","modified_gmt":"2026-10-14T08:05:21","slug":"predicting-diatomic-mass-spectra","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/predicting-diatomic-mass-spectra\/","title":{"rendered":"Predicting Diatomic Mass Spectra"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-predicting-diatomic-mass-spectra-9ch0-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --soft-orange: #fff7ed;\n      --gold: #c9973a;\n      --grey-text: #667085;\n      --body-text: #1f2937;\n      --border: rgba(28, 36, 75, 0.14);\n      --shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      --inner-shadow: 0 10px 26px rgba(28, 36, 75, 0.08);\n      font-family: Poppins, Arial, sans-serif;\n      color: var(--navy);\n      background: #ffffff;\n    }\n\n    .ols-revision-page * { box-sizing: border-box; }\n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n\n    \n    \n\n    .ols-main {\n      min-width: 0;\n      max-width: 970px;\n    }\n\n    .ols-breadcrumbs {\n      display: flex;\n      flex-wrap: wrap;\n      gap: 8px;\n      margin: 10px 0 22px;\n      font-size: 15px;\n      color: var(--grey-text);\n    }\n\n    .ols-breadcrumbs a,\n    .ols-breadcrumbs span {\n      color: var(--grey-text);\n      text-decoration: none;\n      font-weight: 600;\n    }\n\n    .ols-breadcrumbs a:hover {\n      color: var(--blue);\n      text-decoration: underline;\n      text-underline-offset: 3px;\n    }\n\n    .ols-title-card,\n    .ols-note-card,\n    .ols-h5p-card,\n    .ols-related-card,\n    .ols-faq-card,\n    .ols-quicksnap-card {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 28px;\n      box-shadow: var(--shadow);\n      padding: 34px;\n      margin-bottom: 24px;\n      overflow: hidden;\n    }\n\n    .ols-title-card { background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%); }\n\n    .ols-title-card h1 {\n      margin: 0 0 18px;\n      font-size: clamp(36px, 5vw, 58px);\n      line-height: 1.08;\n      font-weight: 800;\n      letter-spacing: -0.04em;\n      color: #111827;\n    }\n\n    .ols-page-intro {\n      font-size: 19px;\n      line-height: 1.7;\n      font-weight: 300;\n      color: var(--body-text);\n      margin: 0 0 22px;\n    }\n\n    .ols-badges {\n      display: flex;\n      flex-direction: column;\n      align-items: flex-start;\n      gap: 12px;\n      margin-bottom: 22px;\n    }\n\n    .ols-badge {\n      display: inline-flex;\n      align-items: center;\n      padding: 9px 14px;\n      border-radius: 999px;\n      background: #ffffff;\n      border: 1px solid var(--border);\n      font-size: 15px;\n      font-weight: 600;\n      color: var(--navy);\n    }\n\n    .ols-author {\n      display: flex;\n      align-items: center;\n      gap: 20px;\n      padding: 28px;\n      border-radius: 28px;\n      background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n      border: 1px solid rgba(28,36,75,0.12);\n      box-shadow: 0 18px 45px rgba(28,36,75,0.10);\n      margin-top: 22px;\n    }\n\n    .ols-author-avatar-img {\n      width: 92px;\n      height: 92px;\n      border-radius: 50%;\n      object-fit: cover;\n      object-position: center;\n      flex-shrink: 0;\n      border: 4px solid #ffffff;\n      box-shadow: 0 14px 32px rgba(28,36,75,0.18), 0 0 0 1px rgba(28,36,75,0.10);\n      transition: transform 0.25s ease, box-shadow 0.25s ease;\n    }\n\n    .ols-author:hover .ols-author-avatar-img {\n      transform: scale(1.04);\n      box-shadow: 0 20px 42px rgba(28,36,75,0.22), 0 0 0 1px rgba(28,36,75,0.10);\n    }\n\n    .ols-author-content { min-width: 0; }\n\n    .ols-author-title {\n      margin: 0 0 4px;\n      font-size: clamp(24px,3vw,34px);\n      line-height: 1.15;\n      font-weight: 700;\n      color: var(--navy);\n      letter-spacing: -0.03em;\n    }\n\n    .ols-author-description {\n      margin: 0;\n      font-size: 17px;\n      line-height: 1.7;\n      font-weight: 300;\n      color: var(--grey-text);\n    }\n\n    .ols-linkedin-pill {\n      display: inline-flex;\n      align-items: center;\n      justify-content: center;\n      gap: 10px;\n      margin-top: 16px;\n      padding: 11px 18px;\n      border-radius: 999px;\n      background: linear-gradient(135deg,#0A66C2,#004182);\n      color: #ffffff;\n      text-decoration: none;\n      font-size: 14px;\n      line-height: 1;\n      font-weight: 700;\n      letter-spacing: 0.01em;\n      box-shadow: 0 10px 22px rgba(10,102,194,0.24);\n      position: relative;\n      overflow: hidden;\n      transition: transform 0.22s ease, box-shadow 0.22s ease;\n    }\n\n    .ols-linkedin-pill::before {\n      content: \"\";\n      position: absolute;\n      top: 0;\n      left: -120%;\n      width: 100%;\n      height: 100%;\n      background: linear-gradient(120deg, rgba(255,255,255,0) 0%, rgba(255,255,255,0.28) 50%, rgba(255,255,255,0) 100%);\n      transition: left 0.7s ease;\n    }\n\n    .ols-linkedin-pill:hover {\n      transform: translateY(-3px) scale(1.03);\n      box-shadow: 0 16px 34px rgba(10,102,194,0.34), 0 0 0 6px rgba(10,102,194,0.10);\n      color: #ffffff;\n    }\n\n    .ols-linkedin-pill:hover::before { left: 120%; }\n\n    .ols-linkedin-icon {\n      width: 18px;\n      height: 18px;\n      display: block;\n      flex-shrink: 0;\n    }\n\n    .ols-note-card.soft { background: linear-gradient(135deg, #ffffff 0%, var(--soft-red) 100%); }\n    .ols-note-card.purple { background: linear-gradient(135deg, #ffffff 0%, var(--soft-purple) 100%); }\n    .ols-note-card.orange { background: linear-gradient(135deg, #ffffff 0%, var(--soft-orange) 100%); }\n\n    .ols-note-title {\n      display: flex;\n      align-items: center;\n      gap: 14px;\n      margin-bottom: 20px;\n    }\n\n    .ols-note-icon {\n      width: 52px;\n      height: 52px;\n      border-radius: 16px;\n      background: var(--navy);\n      color: #ffffff;\n      display: grid;\n      place-items: center;\n      font-size: 24px;\n      font-weight: 800;\n      flex-shrink: 0;\n    }\n\n    .ols-note-title h2,\n    .ols-h5p-card h2,\n    .ols-related-card h2,\n    .ols-faq-card h2,\n    .ols-quicksnap-card h2 {\n      margin: 0;\n      font-size: clamp(28px, 3.5vw, 42px);\n      line-height: 1.15;\n      font-weight: 800;\n      color: #111827;\n      letter-spacing: -0.03em;\n    }\n\n    .ols-h5p-card h2,\n    .ols-related-card h2,\n    .ols-faq-card h2,\n    .ols-quicksnap-card h2 { margin-bottom: 14px; }\n\n    .ols-note-card p,\n    .ols-note-card li {\n      font-size: clamp(15px, 1.25vw, 17px);\n      line-height: 1.65;\n      font-weight: 300;\n      color: var(--body-text);\n    }\n\n    .ols-h5p-card p,\n    .ols-related-card p,\n    .ols-faq-card p,\n    .ols-quicksnap-card p {\n      font-size: clamp(15px, 1.3vw, 18px);\n      line-height: 1.65;\n      font-weight: 300;\n      color: var(--body-text);\n    }\n\n    .ols-note-card strong,\n    .ols-h5p-card strong,\n    .ols-related-card strong,\n    .ols-faq-card strong,\n    .ols-quicksnap-card strong {\n      font-weight: 700;\n      color: var(--navy);\n    }\n\n    .ols-note-card ul,\n    .ols-note-card ol {\n      margin: 0;\n      padding-left: 22px;\n    }\n\n    .ols-key-box {\n      margin-top: 20px;\n      background: var(--soft-green);\n      border: 1px solid rgba(63, 143, 70, 0.25);\n      border-radius: 20px;\n      padding: 18px 20px;\n    }\n\n    .ols-key-box p {\n      margin: 0;\n      font-weight: 400;\n      color: var(--navy);\n    }\n\n    .ols-formula-box {\n      margin: 22px 0 4px;\n      padding: 22px;\n      border-radius: 22px;\n      border: 1px solid rgba(37, 99, 235, 0.18);\n      background: linear-gradient(135deg, #ffffff, var(--soft-blue));\n      box-shadow: var(--inner-shadow);\n      text-align: center;\n    }\n\n    .ols-formula-box p {\n      margin: 0;\n      font-size: clamp(20px, 2.6vw, 32px);\n      line-height: 1.45;\n      font-weight: 800;\n      color: var(--navy);\n      overflow-wrap: anywhere;\n    }\n\n    .ols-formula-box small {\n      display: block;\n      margin-top: 10px;\n      font-size: 14px;\n      line-height: 1.55;\n      color: var(--grey-text);\n      font-weight: 400;\n    }\n\n    .ols-rule-list {\n      display: grid;\n      gap: 14px;\n      margin-top: 18px;\n    }\n\n    .ols-rule-item {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-left: 5px solid var(--blue);\n      border-radius: 18px;\n      padding: 18px;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-rule-item h3 {\n      margin: 0 0 8px;\n      font-size: 20px;\n      line-height: 1.25;\n      color: var(--navy);\n    }\n\n    .ols-rule-item p {\n      margin: 0;\n      font-size: 15px;\n      line-height: 1.6;\n    }\n\n    .ols-figure-card {\n      margin: 26px 0 4px;\n      border: 1px solid var(--border);\n      border-radius: 26px;\n      overflow: hidden;\n      background: #ffffff;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-figure-image {\n      width: 100%;\n      min-height: 260px;\n      display: flex;\n      align-items: center;\n      justify-content: center;\n      background: #ffffff;\n      padding: 20px;\n    }\n\n    .ols-figure-image img {\n      max-width: 100%;\n      height: auto;\n      display: block;\n    }\n\n    .ols-figure-caption {\n      padding: 20px 24px 22px;\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n      border-top: 1px solid var(--border);\n    }\n\n    .ols-figure-caption p {\n      margin: 0;\n      color: #5f6b85;\n      font-size: clamp(15px, 1.3vw, 17px);\n      line-height: 1.6;\n      font-weight: 300;\n      font-style: italic;\n    }\n\n    .ols-table-wrap {\n      overflow: hidden;\n      border-radius: 22px;\n      border: 1px solid var(--border);\n      background: #ffffff;\n      margin-top: 18px;\n    }\n\n    .ols-table {\n      width: 100%;\n      border-collapse: collapse;\n      table-layout: fixed;\n    }\n\n    .ols-table th {\n      background: var(--navy);\n      color: #ffffff;\n      padding: 16px;\n      text-align: left;\n      font-size: clamp(14px, 1.2vw, 17px);\n      font-weight: 600;\n      overflow-wrap: anywhere;\n    }\n\n    .ols-table td {\n      padding: 16px;\n      border-bottom: 1px solid var(--border);\n      font-size: clamp(14px, 1.15vw, 16px);\n      line-height: 1.45;\n      color: var(--body-text);\n      vertical-align: top;\n      overflow-wrap: anywhere;\n    }\n\n    .ols-table tr:last-child td { border-bottom: none; }\n\n    .ols-worked-grid {\n      display: grid;\n      gap: 14px;\n      margin-top: 20px;\n    }\n\n    .ols-worked-step {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 18px;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-worked-step h3 {\n      margin: 0 0 8px;\n      font-size: 20px;\n      line-height: 1.25;\n      color: var(--navy);\n    }\n\n    .ols-worked-step p {\n      margin: 0;\n      font-size: 16px;\n      line-height: 1.65;\n    }\n\n    .ols-h5p-card { background: linear-gradient(135deg, #ffffff 0%, #f7f0ff 100%); }\n\n    .ols-h5p-grid {\n      display: grid;\n      grid-template-columns: 1fr;\n      gap: 16px;\n      margin-top: 22px;\n    }\n\n    .ols-h5p-frame {\n      padding: 18px;\n      border-radius: 24px;\n      background: #ffffff;\n      border: 1px solid var(--border);\n      box-shadow: inset 0 0 0 1px rgba(28, 36, 75, 0.03);\n    }\n\n    .ols-quicksnap-card {\n      background:\n        radial-gradient(circle at top left, rgba(201,151,58,0.15), transparent 30%),\n        linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n    }\n\n    .ols-snap-list {\n      display: grid;\n      gap: 12px;\n      margin-top: 18px;\n    }\n\n    .ols-snap-item {\n      display: grid;\n      grid-template-columns: 42px 1fr;\n      gap: 12px;\n      align-items: start;\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 16px;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-snap-number {\n      width: 42px;\n      height: 42px;\n      border-radius: 14px;\n      background: var(--navy);\n      color: #ffffff;\n      display: grid;\n      place-items: center;\n      font-weight: 800;\n    }\n\n    .ols-snap-item p {\n      margin: 0;\n      font-size: 16px;\n      line-height: 1.6;\n    }\n\n    .ols-course-cta {\n      width: 100%;\n      margin: 30px 0 24px;\n      font-family: Poppins, Arial, sans-serif;\n    }\n\n    .ols-course-cta,\n    .ols-course-cta * { box-sizing: border-box; }\n\n    .ols-course-cta-card {\n      overflow: hidden;\n      border-radius: 30px;\n      border: 1px solid var(--border);\n      background:\n        radial-gradient(circle at top left, rgba(37, 99, 235, 0.16), transparent 34%),\n        linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n      box-shadow: var(--shadow);\n      padding: 34px;\n      text-align: center;\n    }\n\n    .ols-course-cta-pill {\n      display: inline-flex;\n      align-items: center;\n      justify-content: center;\n      padding: 8px 14px;\n      border-radius: 999px;\n      background: rgba(37, 99, 235, 0.10);\n      color: var(--blue);\n      border: 1px solid rgba(37, 99, 235, 0.18);\n      font-size: 13px;\n      font-weight: 700;\n      margin-bottom: 14px;\n    }\n\n    .ols-course-cta-card h2 {\n      margin: 0 0 12px;\n      font-size: clamp(30px, 4vw, 46px);\n      line-height: 1.15;\n      font-weight: 800;\n      color: #111827;\n      letter-spacing: -0.03em;\n    }\n\n    .ols-course-cta-card p {\n      margin: 0 auto 22px;\n      max-width: 750px;\n      font-size: 18px;\n      line-height: 1.65;\n      font-weight: 300;\n      color: var(--body-text);\n    }\n\n    .ols-cta-button {\n      display: inline-flex;\n      align-items: center;\n      justify-content: center;\n      padding: 14px 26px;\n      border-radius: 999px;\n      background: var(--navy);\n      color: #ffffff;\n      text-decoration: none;\n      font-weight: 700;\n      box-shadow: 0 12px 26px rgba(28,36,75,0.18);\n      transition: transform 0.2s ease, box-shadow 0.2s ease;\n    }\n\n    .ols-cta-button:hover {\n      transform: translateY(-2px);\n      box-shadow: 0 16px 34px rgba(28,36,75,0.22);\n      color: #ffffff;\n    }\n\n    .ols-faq-list {\n      display: grid;\n      gap: 14px;\n      margin-top: 18px;\n    }\n\n    .ols-faq-item {\n      background: #ffffff;\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 18px 20px;\n      box-shadow: var(--inner-shadow);\n    }\n\n    .ols-faq-item h3 {\n      margin: 0 0 8px;\n      font-size: 20px;\n      line-height: 1.3;\n      color: var(--navy);\n    }\n\n    .ols-faq-item p {\n      margin: 0;\n      font-size: 16px;\n      line-height: 1.65;\n      color: var(--body-text);\n    }\n\n    .ols-related-grid {\n      display: grid;\n      grid-template-columns: repeat(3, minmax(0, 1fr));\n      gap: 16px;\n      margin-top: 18px;\n    }\n\n    .ols-related-item {\n      border: 1px solid var(--border);\n      border-radius: 18px;\n      padding: 18px;\n      background: #ffffff;\n      color: var(--navy);\n      text-decoration: none;\n      font-weight: 600;\n      line-height: 1.5;\n      transition: transform 0.2s ease, box-shadow 0.2s ease;\n    }\n\n    .ols-related-item:hover {\n      transform: translateY(-2px);\n      box-shadow: 0 10px 22px rgba(28, 36, 75, 0.08);\n      color: var(--blue);\n    }\n\n    .ols-attribution-card {\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n      border: 1px solid rgba(28, 36, 75, 0.14);\n      border-radius: 28px;\n      box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      padding: 34px;\n      margin-bottom: 24px;\n      overflow: hidden;\n      font-family: Poppins, Arial, sans-serif;\n      box-sizing: border-box;\n    }\n\n    .ols-attribution-card,\n    .ols-attribution-card * { box-sizing: border-box; }\n\n    .ols-attribution-card p {\n      margin: 0;\n      font-size: 14px;\n      line-height: 1.65;\n      font-weight: 300;\n      color: #667085;\n    }\n\n    .ols-attribution-card strong {\n      font-weight: 700;\n      color: #1C244B;\n    }\n\n    @media (max-width: 1050px) {\n      \n      \n      \n      \n      .ols-main { max-width: none; }\n      .ols-related-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }\n    }\n\n    @media (max-width: 760px) {\n      \n      .ols-title-card,\n      .ols-note-card,\n      .ols-h5p-card,\n      .ols-related-card,\n      .ols-faq-card,\n      .ols-quicksnap-card,\n      .ols-course-cta-card,\n      .ols-attribution-card {\n        padding: 24px 18px;\n        border-radius: 22px;\n      }\n\n      .ols-note-title { align-items: flex-start; }\n      \n      \n      .ols-figure-card { border-radius: 22px; }\n      .ols-figure-image { min-height: 210px; padding: 14px; }\n      .ols-figure-caption { padding: 18px; }\n\n      .ols-table-wrap {\n        border: none;\n        background: transparent;\n      }\n\n      .ols-table,\n      .ols-table thead,\n      .ols-table tbody,\n      .ols-table th,\n      .ols-table td,\n      .ols-table tr {\n        display: block;\n        width: 100%;\n      }\n\n      .ols-table {\n        border-collapse: separate;\n        border-spacing: 0;\n      }\n\n      .ols-table thead { display: none; }\n\n      .ols-table tr {\n        margin-bottom: 14px;\n        border: 1px solid var(--border);\n        border-radius: 18px;\n        overflow: hidden;\n        background: #ffffff;\n        box-shadow: var(--inner-shadow);\n      }\n\n      .ols-table td {\n        border-bottom: 1px solid var(--border);\n        padding: 14px 16px;\n        overflow-wrap: anywhere;\n      }\n\n      .ols-table td:last-child { border-bottom: none; }\n\n      .ols-table td::before {\n        content: attr(data-label);\n        display: block;\n        margin-bottom: 6px;\n        font-size: 13px;\n        font-weight: 700;\n        color: var(--blue);\n      }\n\n      .ols-author {\n        align-items: flex-start;\n        padding: 22px 18px;\n        border-radius: 22px;\n      }\n\n      .ols-author-avatar-img {\n        width: 72px;\n        height: 72px;\n      }\n\n      .ols-author-title { font-size: 24px; }\n      .ols-author-description { font-size: 15px; }\n\n      .ols-snap-item {\n        grid-template-columns: 1fr;\n      }\n    }\n\n    .ols-zoom-card, .ols-zoom-card * { box-sizing: border-box; }\n    .ols-zoom-card { display: block !important; margin: 26px 0 34px !important; border: 1px solid rgba(28, 36, 75, 0.14) !important; border-radius: 26px !important; background: #ffffff !important; box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10) !important; overflow: visible !important; position: relative !important; z-index: 1 !important; isolation: isolate !important; }\n    .ols-zoom-card:hover { z-index: 50 !important; }\n    .ols-zoom-card-image { display: flex !important; align-items: center !important; justify-content: center !important; width: 100% !important; min-height: 330px !important; padding: 20px !important; background: #ffffff !important; overflow: visible !important; border-top-left-radius: 26px !important; border-top-right-radius: 26px !important; position: relative !important; z-index: 2 !important; }\n    .ols-zoom-card img.ols-zoomable-img { display: block !important; width: 100% !important; max-width: 100% !important; height: auto !important; border-radius: 18px !important; cursor: default !important; pointer-events: auto !important; user-select: none !important; -webkit-user-drag: none !important; transform: translateZ(0) scale(1) !important; transform-origin: center center !important; transition: transform 0.32s ease, box-shadow 0.32s ease, filter 0.32s ease !important; position: relative !important; z-index: 2 !important; }\n    @media (hover: hover) and (pointer: fine) { .ols-zoom-card img.ols-zoomable-img:hover { transform: translateZ(0) scale(1.45) !important; box-shadow: 0 28px 70px rgba(28, 36, 75, 0.34) !important; filter: saturate(1.02) contrast(1.01) !important; z-index: 100 !important; } }\n    .ols-zoom-card-caption { padding: 18px 22px 20px !important; background: linear-gradient(135deg, #ffffff, #f8fbff) !important; border-bottom-left-radius: 26px !important; border-bottom-right-radius: 26px !important; position: relative !important; z-index: 1 !important; }\n    .ols-zoom-card-caption p { margin: 0 !important; color: #5f6b85 !important; font-size: 15px !important; line-height: 1.65 !important; font-weight: 300 !important; font-style: italic !important; font-family: Poppins, Arial, sans-serif !important; }\n    .ols-zoom-card img.ols-lightbox-target { cursor: zoom-in !important; }\n    @media (max-width: 760px) { .ols-zoom-card { border-radius: 22px !important; overflow: hidden !important; } .ols-zoom-card-image { min-height: auto !important; padding: 12px !important; overflow: hidden !important; } .ols-zoom-card img.ols-zoomable-img, .ols-zoom-card img.ols-zoomable-img:hover { transform: none !important; box-shadow: none !important; } }\n    .ols-image-lightbox { position: fixed; inset: 0; z-index: 999999; display: none; align-items: center; justify-content: center; padding: 34px; background: rgba(10, 15, 35, 0.86); backdrop-filter: blur(8px); -webkit-backdrop-filter: blur(8px); }\n    .ols-image-lightbox.is-open { display: flex; }\n    .ols-image-lightbox-inner { position: relative; width: min(96vw, 1500px); max-height: 92vh; display: flex; align-items: center; 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} .ols-image-lightbox-close { top: 10px; right: 10px; width: 42px; height: 42px; font-size: 26px; } }\n  <\/style>\n\n  <aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Topic 1 Atomic Structure and The Periodic Table<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/atomic-structure\/\">Atomic Structure<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/\">Mass Spectrometry<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/the-mass-spectrometer\/\">The Mass Spectrometer<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/ram-calculations\/\">RAM Calculations<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/predicting-diatomic-mass-spectra\/\">Predicting Diatomic Mass Spectra<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/\">Identifying Compounds from Mass Spectra<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/electron-configuration\/\">Electron Configuration<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/\">Ionisation Energy<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/introduction-to-ionisation-energy\/\">Introduction to Ionisation Energy<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/successive-ionisation-energies\/\">Successive Ionisation Energies<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-period\/\">Trends in a Period<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/\">Trends in a Group<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/periodic-trends\/\">Periodic Trends<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Next Topics<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/\">Bonding &amp; Structure<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-3-redox-i\/\">Redox I<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/\">Inorganic Chemistry &amp; The Periodic Table<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n    var matched = null;\r\n    var matchedLength = 0;\r\n\r\n    sidebar.querySelectorAll('.active, .active-main, .parent-active').forEach(function(item) {\r\n      item.classList.remove('active', 'active-main', 'parent-active');\r\n    });\r\n\r\n    sidebar.querySelectorAll('a[data-ols-disabled-parent=\"1\"], a[aria-current]').forEach(function(a) {\r\n      a.removeAttribute('aria-current');\r\n      a.removeAttribute('tabindex');\r\n      a.removeAttribute('data-ols-disabled-parent');\r\n    });\r\n\r\n    links.forEach(function(a) {\r\n      try {\r\n        var href = a.getAttribute('href');\r\n\r\n        if (!href || href === '#' || href.charAt(0) === '#') {\r\n          return;\r\n        }\r\n\r\n        var linkPath = normalisePath(new URL(href, window.location.origin).pathname);\r\n\r\n        if (!linkPath) {\r\n          return;\r\n        }\r\n\r\n        if (currentPath === linkPath || currentPath.indexOf(linkPath + '\/') === 0) {\r\n          if (linkPath.length > matchedLength) {\r\n            matched = a;\r\n            matchedLength = linkPath.length;\r\n          }\r\n        }\r\n      } catch(e) {}\r\n    });\r\n\r\n    if (matched) {\r\n      var matchedLi = matched.closest('li');\r\n      var parentSub = matched.closest('.ols-subtopic-list');\r\n\r\n      if (parentSub) {\r\n        if (matchedLi) {\r\n          matchedLi.classList.add('active');\r\n          matched.setAttribute('aria-current', 'page');\r\n        }\r\n\r\n        var parentLi = parentSub.closest('li');\r\n\r\n        if (parentLi) {\r\n          parentLi.classList.add('parent-active', 'active-main');\r\n\r\n          var parentLink = parentLi.querySelector(':scope > a');\r\n\r\n          if (parentLink) {\r\n            parentLink.setAttribute('aria-current', 'true');\r\n            parentLink.setAttribute('tabindex', '-1');\r\n            parentLink.setAttribute('data-ols-disabled-parent', '1');\r\n          }\r\n        }\r\n      } else {\r\n        if (matchedLi) {\r\n          matchedLi.classList.add('parent-active', 'active-main');\r\n          matched.setAttribute('aria-current', 'page');\r\n          matched.setAttribute('tabindex', '-1');\r\n          matched.setAttribute('data-ols-disabled-parent', '1');\r\n        }\r\n      }\r\n    }\r\n\r\n    return true;\r\n  }\r\n\r\n  if (!highlightActive()) {\r\n    document.addEventListener('DOMContentLoaded', highlightActive);\r\n  }\r\n})();\r\n<\/script>\n\n  <main class=\"ols-main\">\n      <nav class=\"ols-breadcrumbs\" aria-label=\"Breadcrumb\">\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\">Revision Notes<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\">A Level Chemistry<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\">Edexcel<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/\">Topic 1 Atomic Structure &amp; The Periodic Table<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/\">Mass Spectrometry<\/a> \/\n        <span>Predicting Diatomic Mass Spectra<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Predicting Diatomic Mass Spectra<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to predicting the molecular ion peaks for diatomic molecules from isotope abundance data, using chlorine, Cl<sub>2<\/sub>, as the key example.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Unit: Paper 1<\/div>\n          <div class=\"ols-badge\">Topic 1: Atomic Structure &amp; The Periodic Table<\/div>\n          <div class=\"ols-badge\">9CH0\/01<\/div>\n        <\/div>\n      <\/header>\n\n      <section class=\"ols-h5p-card ols-h5p-inline ols-h5p-recap\">\n<span class=\"ols-h5p-kicker\">Before you start<\/span>\n<h2>GCSE Recap: Isotopes and Diatomic Molecules<\/h2>\n<p>Before you start, check what you remember about diatomic elements and isotopes.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"607\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">1<\/div><h2>Why Diatomic Molecules Give Several Peaks<\/h2><\/div>\n        <p>A diatomic molecule contains <strong>two atoms joined together<\/strong>. If the element has more than one isotope, different isotope pairings are possible in the molecule.<\/p>\n        <p>For chlorine, the two main isotopes are <sup>35<\/sup>Cl and <sup>37<\/sup>Cl. This means a molecule of Cl<sub>2<\/sub> can contain two <sup>35<\/sup>Cl atoms, one of each isotope, or two <sup>37<\/sup>Cl atoms.<\/p>\n        <div class=\"ols-key-box\"><p><strong>Key idea:<\/strong> each possible isotope pairing gives a different molecular mass, so the molecular ion region of the mass spectrum shows more than one peak.<\/p><\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">2<\/div><h2>List Every Possible Isotope Pair<\/h2><\/div>\n        <p>Start by listing the possible combinations. This prevents you from missing the mixed molecule, which is the most common exam error in this calculation.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Combination<\/th>\n                <th>Molecule<\/th>\n                <th>Molecular mass<\/th>\n                <th>Expected m\/z for 1+ ion<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Combination\">Light + light<\/td>\n                <td data-label=\"Molecule\"><sup>35<\/sup>Cl-<sup>35<\/sup>Cl<\/td>\n                <td data-label=\"Molecular mass\">35 + 35 = 70<\/td>\n                <td data-label=\"Expected m\/z for 1+ ion\">70<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Combination\">Light + heavy<\/td>\n                <td data-label=\"Molecule\"><sup>35<\/sup>Cl-<sup>37<\/sup>Cl<\/td>\n                <td data-label=\"Molecular mass\">35 + 37 = 72<\/td>\n                <td data-label=\"Expected m\/z for 1+ ion\">72<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Combination\">Heavy + light<\/td>\n                <td data-label=\"Molecule\"><sup>37<\/sup>Cl-<sup>35<\/sup>Cl<\/td>\n                <td data-label=\"Molecular mass\">37 + 35 = 72<\/td>\n                <td data-label=\"Expected m\/z for 1+ ion\">72<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Combination\">Heavy + heavy<\/td>\n                <td data-label=\"Molecule\"><sup>37<\/sup>Cl-<sup>37<\/sup>Cl<\/td>\n                <td data-label=\"Molecular mass\">37 + 37 = 74<\/td>\n                <td data-label=\"Expected m\/z for 1+ ion\">74<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\"><p><strong>Exam focus:<\/strong> the two mixed arrangements have the same molecular mass, so they contribute to the same m\/z peak.<\/p><\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: List the Pairs for a New Element<\/h2>\n<p>Write out every isotope pair on paper, then type the m\/z values.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-251\" class=\"h5p-iframe\" data-content-id=\"251\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Diatomic Mass Spectra Fill in the Blanks: Isotope Pairs for Bromine, Oxygen and Iodine\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">3<\/div><h2>Multiply the Isotopic Abundances<\/h2><\/div>\n        <p>Convert the percentage abundances into decimals, then multiply the two isotope abundances for each possible molecule.<\/p>\n        <p>For chlorine: <sup>35<\/sup>Cl = 75% = 0.75 and <sup>37<\/sup>Cl = 25% = 0.25. These are the rounded values used in exam questions: a 3:1 ratio, which gives A<sub>r<\/sub> = 35.5.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Molecule<\/th>\n                <th>Relative abundance calculation<\/th>\n                <th>Relative abundance<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Molecule\"><sup>35<\/sup>Cl-<sup>35<\/sup>Cl<\/td>\n                <td data-label=\"Relative abundance calculation\">0.75 \u00d7 0.75<\/td>\n                <td data-label=\"Relative abundance\">0.5625<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Molecule\"><sup>35<\/sup>Cl-<sup>37<\/sup>Cl<\/td>\n                <td data-label=\"Relative abundance calculation\">0.75 \u00d7 0.25<\/td>\n                <td data-label=\"Relative abundance\">0.1875<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Molecule\"><sup>37<\/sup>Cl-<sup>35<\/sup>Cl<\/td>\n                <td data-label=\"Relative abundance calculation\">0.25 \u00d7 0.75<\/td>\n                <td data-label=\"Relative abundance\">0.1875<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Molecule\"><sup>37<\/sup>Cl-<sup>37<\/sup>Cl<\/td>\n                <td data-label=\"Relative abundance calculation\">0.25 \u00d7 0.25<\/td>\n                <td data-label=\"Relative abundance\">0.0625<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\"><p><strong>Remember:<\/strong> do not add the isotope abundances for a molecule. Multiply them, because both atoms must be chosen together.<\/p><\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Half the Atoms, Half the Molecules?<\/h2>\n<p>Decide whether the statement about bromine molecules is true or false.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-608\" class=\"h5p-iframe\" data-content-id=\"608\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Diatomic Mass Spectra True or False: Half the Atoms, Half the Molecules?\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">4<\/div><h2>Combine Equivalent Mixed Isotope Molecules<\/h2><\/div>\n        <p>The molecules <sup>35<\/sup>Cl-<sup>37<\/sup>Cl and <sup>37<\/sup>Cl-<sup>35<\/sup>Cl have the same molecular mass. Both have molecular mass 72, so their abundances are added together.<\/p>\n\n        <div class=\"ols-formula-box\">\n          <p>0.1875 + 0.1875 = 0.375<\/p>\n          <small>This gives the total relative abundance of the m\/z 72 peak.<\/small>\n        <\/div>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Molecular ion<\/th>\n                <th>m\/z<\/th>\n                <th>Total relative abundance<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Molecular ion\"><sup>35<\/sup>Cl-<sup>35<\/sup>Cl<sup>+<\/sup><\/td>\n                <td data-label=\"m\/z\">70<\/td>\n                <td data-label=\"Total relative abundance\">0.5625<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Molecular ion\"><sup>35<\/sup>Cl-<sup>37<\/sup>Cl<sup>+<\/sup> and <sup>37<\/sup>Cl-<sup>35<\/sup>Cl<sup>+<\/sup><\/td>\n                <td data-label=\"m\/z\">72<\/td>\n                <td data-label=\"Total relative abundance\">0.375<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Molecular ion\"><sup>37<\/sup>Cl-<sup>37<\/sup>Cl<sup>+<\/sup><\/td>\n                <td data-label=\"m\/z\">74<\/td>\n                <td data-label=\"Total relative abundance\">0.0625<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: The Mixed Isotope Peak<\/h2>\n<p>Work out the total abundance of the mixed molecules for an element with 60% and 40% isotopes.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-252\" class=\"h5p-iframe\" data-content-id=\"252\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Diatomic Mass Spectra MCQ: Abundance of the Mixed Isotope Peak\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">5<\/div><h2>Convert Relative Abundances into a Peak Ratio<\/h2><\/div>\n        <p>To find the simplest whole number ratio, divide all of the relative abundances by the smallest value.<\/p>\n\n        <div class=\"ols-worked-grid\">\n          <div class=\"ols-worked-step\">\n            <h3>m\/z 70<\/h3>\n            <p>0.5625 \u00f7 0.0625 = <strong>9<\/strong><\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>m\/z 72<\/h3>\n            <p>0.375 \u00f7 0.0625 = <strong>6<\/strong><\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>m\/z 74<\/h3>\n            <p>0.0625 \u00f7 0.0625 = <strong>1<\/strong><\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-formula-box\">\n          <p>Cl<sub>2<\/sub> molecular ion peaks: m\/z 70 : 72 : 74 = 9 : 6 : 1<\/p>\n          <small>The middle peak is larger than the m\/z 74 peak because there are two ways to make a mixed isotope molecule.<\/small>\n        <\/div>\n        <p>A real spectrum of Cl<sub>2<\/sub> shows two more peaks at lower m\/z.<\/p>\n<p>Some Cl<sub>2<\/sub><sup>+<\/sup> ions break apart in the instrument and give <strong>atomic ions<\/strong>: <sup>35<\/sup>Cl<sup>+<\/sup> at m\/z 35 and <sup>37<\/sup>Cl<sup>+<\/sup> at m\/z 37.<\/p>\n<p>Their heights are in the ratio 3:1, the same as the isotope abundances.<\/p>\n        <div class=\"ols-key-box\"><p><strong>Exam focus:<\/strong> the full spectrum of chlorine has five peaks. m\/z 35 and 37 (3:1) are atomic ions, Cl<sup>+<\/sup>. m\/z 70, 72 and 74 (9:6:1) are molecular ions, Cl<sub>2<\/sub><sup>+<\/sup>.<\/p><\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Predict the Whole Pattern<\/h2>\n<p>Predict the m\/z values and the simplest peak ratio on paper before you flip each card.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-253\" class=\"h5p-iframe\" data-content-id=\"253\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Diatomic Mass Spectra Flip Cards: From Isotope Data to a Peak Ratio\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <div class=\"ols-zoom-card\">\n        <div class=\"ols-zoom-card-image\">\n          <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t2-img-16-cl2predict.jpg\" alt=\"Four-step worked example predicting the Cl\u2082 mass spectrum: peaks at m\/z 70, 72 and 74 in the ratio 9 : 6 : 1\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>The m\/z 70, 72 and 74 peaks arise from the three possible molecular masses of Cl<sub>2<\/sub><sup>+<\/sup>.<\/p>\n        <\/div>\n      <\/div>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">6<\/div><h2>Use the Pattern to Check Your Answer<\/h2><\/div>\n        <p>The 9:6:1 peak ratio is not random. It comes from the isotope abundance ratio of chlorine, which is approximately 3:1 for <sup>35<\/sup>Cl:<sup>37<\/sup>Cl.<\/p>\n        <p>For a diatomic molecule, the combinations follow the pattern:<\/p>\n\n        <div class=\"ols-formula-box\">\n          <p>3 \u00d7 3 : 2 \u00d7 3 \u00d7 1 : 1 \u00d7 1 = 9 : 6 : 1<\/p>\n          <small>The factor of 2 appears because the mixed molecule can form in two equivalent orders.<\/small>\n        <\/div>\n\n        <div class=\"ols-key-box\"><p><strong>Exam focus:<\/strong> if the chlorine molecular ion peaks are in a 9:6:1 ratio, this supports the presence of two chlorine atoms in the molecule.<\/p><\/div>\n      <div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t2-img-17-diatomicpatterns.jpg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t2-img-17-diatomicpatterns.jpg\" alt=\"Two stick spectra compared: Cl\u2082 peaks at m\/z 70, 72, 74 in ratio 9 : 6 : 1 and Br\u2082 peaks at m\/z 158, 160, 162 in ratio 1 : 2 : 1\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Two isotopes give three molecular ion peaks 2 units apart: 9 : 6 : 1 for Cl\u2082 and 1 : 2 : 1 for Br\u2082.<\/p><\/div>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Patterns Beyond Chlorine<\/h2>\n<p>In each round, pick the one statement that is accurate.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-254\" class=\"h5p-iframe\" data-content-id=\"254\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Diatomic Mass Spectra Summary: Peak Patterns Beyond Chlorine\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">7<\/div><h2>Common Exam Points<\/h2><\/div>\n        <p>These points help avoid the most frequent mistakes when predicting molecular mass spectra for diatomic molecules.<\/p>\n\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\"><h3>Use molecular mass, not atomic mass<\/h3><p>For Cl<sub>2<\/sub>, the molecular ion peaks are at m\/z 70, 72 and 74. The peaks at m\/z 35 and 37 come from Cl<sup>+<\/sup> atomic ions, not from molecules.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>Remember the mixed molecule twice<\/h3><p><sup>35<\/sup>Cl-<sup>37<\/sup>Cl and <sup>37<\/sup>Cl-<sup>35<\/sup>Cl are equivalent but both contribute to the m\/z 72 peak.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>Multiply probabilities<\/h3><p>To find the relative abundance of a molecule, multiply the abundances of the two isotopes used to form it.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>Use 1+ ions carefully<\/h3><p>When the molecular ion has a single positive charge, the m\/z value is equal to the relative molecular mass of that ion.<\/p><\/div>\n        <\/div>\n      <\/article>\n\n      \n\n      <section class=\"ols-quicksnap-card\">\n        <h2>QuickSnap Summary<\/h2>\n        <p>Predicting a diatomic mass spectrum means combining isotope masses and isotope abundances to find the expected molecular ion peaks.<\/p>\n\n        <div class=\"ols-snap-list\">\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">1<\/div><p>List every possible isotope pair in the diatomic molecule.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">2<\/div><p>Add the isotope mass numbers to find each molecular ion m\/z value.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">3<\/div><p>Multiply isotope abundances to calculate the relative abundance of each pairing.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">4<\/div><p>Add equivalent mixed pair abundances, then divide by the smallest value to get the simplest ratio.<\/p><\/div>\n        <\/div>\n      <\/section>\n\n\n\n      <section class=\"ols-faq-card\">\n        <h2>FAQs<\/h2>\n        <p>These common questions summarise the key calculation ideas for predicting diatomic molecular mass spectra.<\/p>\n\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>Why does Cl<sub>2<\/sub> give peaks at m\/z 70, 72 and 74?<\/h3>\n            <p>Chlorine has two isotopes, <sup>35<\/sup>Cl and <sup>37<\/sup>Cl. The possible Cl<sub>2<\/sub> molecules have masses 35 + 35 = 70, 35 + 37 = 72, and 37 + 37 = 74.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why is the middle Cl<sub>2<\/sub> peak larger than expected?<\/h3>\n            <p>The middle peak includes two equivalent mixed isotope arrangements: <sup>35<\/sup>Cl-<sup>37<\/sup>Cl and <sup>37<\/sup>Cl-<sup>35<\/sup>Cl. Their abundances must be added together.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>How do you calculate the relative abundance of a diatomic molecule?<\/h3>\n            <p>Convert the isotope abundances into decimals, then multiply the two isotope abundances for the atoms in that molecule.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>What is the predicted Cl<sub>2<\/sub> molecular ion peak ratio?<\/h3>\n            <p>Using 75% <sup>35<\/sup>Cl and 25% <sup>37<\/sup>Cl, the predicted molecular ion peaks at m\/z 70, 72 and 74 have a ratio of 9:6:1.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why does a real chlorine spectrum also show peaks at m\/z 35 and 37?<\/h3>\n            <p>Some Cl<sub>2<\/sub><sup>+<\/sup> ions break apart in the instrument to give <sup>35<\/sup>Cl<sup>+<\/sup> and <sup>37<\/sup>Cl<sup>+<\/sup>. These atomic ion peaks are in the 3:1 isotope ratio and are not part of the 9:6:1 molecular ion pattern.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <!-- author card (moved to the end, 10 Oct 2026) -->\n      <div class=\"ols-author\">\n\n    <img decoding=\"async\"\n      class=\"ols-author-avatar-img\"\n      src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n      alt=\"Dr. Mohammed Al-Fatah\"\n    >\n\n    <div class=\"ols-author-content\">\n\n      <h2 class=\"ols-author-title\">\n        Written by: Dr. Mohammed Al-Fatah\n      <\/h2>\n\n      <p class=\"ols-author-description\">\n        Chemistry specialist revision notes for A Level Chemistry.\n      <\/p>\n\n      <a\n        class=\"ols-linkedin-pill\"\n        href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\"\n        target=\"_blank\"\n        rel=\"noopener noreferrer\"\n      >\n\n        <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\">\n          <path d=\"M4.98 3.5C4.98 4.88 3.86 6 2.48 6S0 4.88 0 3.5 1.12 1 2.48 1s2.5 1.12 2.5 2.5zM.5 8h4V24h-4V8zm7 0h3.8v2.2h.1c.5-.9 1.8-2.2 3.9-2.2 4.2 0 5 2.8 5 6.4V24h-4v-7.6c0-1.8 0-4.2-2.6-4.2s-3 2-3 4v7.8h-4V8z\"\/>\n        <\/svg>\n\n        View LinkedIn Profile\n\n      <\/a>\n\n    <\/div>\n\n  <\/div>\n\n\n      <section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Use these linked revision pages to connect diatomic mass spectra with the wider mass spectrometry topic.<\/p>\n\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/the-mass-spectrometer\/\">The Mass Spectrometer<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/ram-calculations\/\">RAM Calculations<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/mass-spectrometry\/\">Identifying Compounds from Mass Spectra<\/a>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-attribution-card ols-attr-std\" aria-label=\"Copyright notice\">\n<style id=\"ols-attribution-card-css\">.ols-attribution-card.ols-attr-std{background:linear-gradient(135deg,#ffffff,#f8fbff);border:1px solid rgba(28,36,75,0.14);border-radius:28px;box-shadow:0 18px 45px rgba(28,36,75,0.10);padding:34px;margin:24px 0;overflow:hidden;font-family:Poppins,Arial,sans-serif;box-sizing:border-box}.ols-attribution-card.ols-attr-std *{box-sizing:border-box}.ols-attribution-card.ols-attr-std p{margin:0;font-size:14px;line-height:1.65;font-weight:300;color:#667085}.ols-attribution-card.ols-attr-std strong{font-weight:700;color:#1C244B}@media (max-width:760px){.ols-attribution-card.ols-attr-std{padding:24px 18px;border-radius:22px}}<\/style>\n<p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n<\/section>\n\n      <!-- OLS Author Copyright Footprint \/ Attribution Card -->\n\n      <div class=\"ols-image-lightbox\" id=\"olsImageLightboxDiatomic9ch0\" aria-hidden=\"true\" role=\"dialog\" aria-modal=\"true\" aria-label=\"Expanded revision image\">\n        <div class=\"ols-image-lightbox-inner\">\n          <button class=\"ols-image-lightbox-close\" type=\"button\" aria-label=\"Close enlarged image\">\u00d7<\/button>\n          <img decoding=\"async\" class=\"ols-image-lightbox-img\" src=\"\" alt=\"\">\n        <\/div>\n      <\/div>\n\n      <script>\n        (function(){\n          var page = document.querySelector(\".ols-predicting-diatomic-mass-spectra-9ch0-page\");\n          if (!page) return;\n          var lightbox = page.querySelector(\"#olsImageLightboxDiatomic9ch0\");\n          if (!lightbox) return;\n          var lightboxImage = lightbox.querySelector(\".ols-image-lightbox-img\");\n          var closeButton = lightbox.querySelector(\".ols-image-lightbox-close\");\n          var clickableImages = page.querySelectorAll(\"img.ols-lightbox-target\");\n\n          function openLightbox(image) {\n            lightboxImage.src = image.currentSrc || image.src;\n            lightboxImage.alt = image.alt || \"Expanded revision image\";\n            lightbox.classList.add(\"is-open\");\n            lightbox.setAttribute(\"aria-hidden\", \"false\");\n            if (!document.body.dataset.olsPreviousOverflow) {\n              document.body.dataset.olsPreviousOverflow = document.body.style.overflow || \"default\";\n            }\n            document.body.style.overflow = \"hidden\";\n          }\n\n          function closeLightbox() {\n            lightbox.classList.remove(\"is-open\");\n            lightbox.setAttribute(\"aria-hidden\", \"true\");\n            lightboxImage.src = \"\";\n            if (document.body.dataset.olsPreviousOverflow) {\n              document.body.style.overflow = document.body.dataset.olsPreviousOverflow === \"default\" ? \"\" : document.body.dataset.olsPreviousOverflow;\n              delete document.body.dataset.olsPreviousOverflow;\n            }\n          }\n\n          clickableImages.forEach(function(image){\n            image.addEventListener(\"click\", function(e){\n              e.preventDefault();\n              e.stopPropagation();\n              openLightbox(image);\n            });\n          });\n\n          closeButton.addEventListener(\"click\", closeLightbox);\n          lightbox.addEventListener(\"click\", function(e){ if (e.target === lightbox) closeLightbox(); });\n          document.addEventListener(\"keydown\", function(e){ if (e.key === \"Escape\" && lightbox.classList.contains(\"is-open\")) closeLightbox(); });\n        })();\n      <\/script>\n    <\/main>\n\n  <script type=\"application\/ld+json\">\n{\n    \"@context\": \"https:\/\/schema.org\",\n    \"@graph\": [\n        {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/predicting-diatomic-mass-spectra\/#webpage\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/predicting-diatomic-mass-spectra\/\",\n            \"name\": \"Predicting Diatomic Mass Spectra - 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The possible Cl2 molecules have masses 35 + 35 = 70, 35 + 37 = 72, and 37 + 37 = 74.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"Why is the middle Cl2 peak larger than expected?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"The middle peak includes two equivalent mixed isotope arrangements: 35Cl-37Cl and 37Cl-35Cl. Their abundances must be added together.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"How do you calculate the relative abundance of a diatomic molecule?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"Convert the isotope abundances into decimals, then multiply the two isotope abundances for the atoms in that molecule.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"What is the predicted Cl2 molecular ion peak ratio?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"Using 75% 35Cl and 25% 37Cl, the predicted molecular ion peaks at m\/z 70, 72 and 74 have a ratio of 9:6:1.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"Why does a real chlorine spectrum also show peaks at m\/z 35 and 37?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"Some Cl2+ ions break apart in the instrument to give 35Cl+ and 37Cl+. These atomic ion peaks are in the 3:1 isotope ratio and are not part of the 9:6:1 molecular ion pattern.\"\n                    }\n                }\n            ]\n        }\n    ]\n}\n<\/script>\n<\/section>\n","protected":false},"excerpt":{"rendered":"<p>Revision Notes \/ A Level Chemistry \/ Edexcel \/ Topic 1 Atomic Structure &amp; The Periodic Table \/ Mass Spectrometry \/ Predicting Diatomic Mass Spectra Predicting Diatomic Mass Spectra A concise revision guide to predicting the molecular ion peaks for diatomic molecules from isotope abundance data, using chlorine, Cl2, as the key example. Unit: Paper [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":4514,"menu_order":2,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-4520","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4520","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/comments?post=4520"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4520\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4514"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=4520"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}