{"id":3992,"date":"2026-05-21T04:56:40","date_gmt":"2026-05-21T03:56:40","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-atomic-structure-and-the-periodic-table\/mass-spectrometry\/predicting-diatomic-mass-spectra\/"},"modified":"2026-05-26T11:06:58","modified_gmt":"2026-05-26T10:06:58","slug":"predicting-diatomic-mass-spectra","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-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-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     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.ols-author-description { font-size: 15px; }\n\n      .ols-snap-item {\n        grid-template-columns: 1fr;\n      }\n    }\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 2 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-international\/topic-2-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-international\/topic-2-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-international\/topic-2-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-international\/topic-2-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-international\/topic-2-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-international\/topic-2-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-international\/topic-2-atomic-structure-and-the-periodic-table\/quantum-model\/\">Quantum Model<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-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-international\/topic-2-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-international\/topic-2-atomic-structure-and-the-periodic-table\/ionisation-energy\/successive-ionisation-energy\/\">Successive Ionisation Energy<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-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 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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-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\">Exam board: Edexcel International<\/div>\n          <div class=\"ols-badge\">Topic 2: Atomic Structure &amp; The Periodic Table<\/div>\n          <div class=\"ols-badge\">Level: A Level Chemistry<\/div>\n        <\/div>\n\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 class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\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      <\/header>\n\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\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.<\/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\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\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\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Cl2-mass-spectrum-and-isotope-analysis.webp\" alt=\"Worked example showing how chlorine isotope abundances predict the mass spectrum of Cl2\">\n          <\/div>\n          <div class=\"ols-figure-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      <\/article>\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      <\/article>\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 peaks are at m\/z 70, 72 and 74, not just 35 and 37.<\/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      <section class=\"ols-h5p-card\">\n        <h2>Check Your Understanding<\/h2>\n        <p>Use these short H5P tasks to test how isotope combinations lead to molecular ion peaks and peak ratios.<\/p>\n\n        <div class=\"ols-h5p-grid\">\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=\"T2.2.3.1 Drag: Predicting Diatomic Mass Spectra Key Concepts\"><\/iframe><\/div><\/div>\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=\"T2.2.3.2 MCQ: Molecular Ion Peaks for Chlorine\"><\/iframe><\/div><\/div>\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=\"T2.2.3.3 MCQ: Mixed Chlorine Molecule Abundance\"><\/iframe><\/div><\/div>\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=\"T2.2.3.4 MCQ: Chlorine Diatomic Peak Ratio\"><\/iframe><\/div><\/div>\n        <\/div>\n      <\/section>\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      <section class=\"ols-course-cta-atomic-structure\" id=\"olsCourseCtaAtomicStructure002\">\n        <style>\n          .ols-course-cta-atomic-structure,\n          .ols-course-cta-atomic-structure * {\n            box-sizing: border-box;\n          }\n      \n          .ols-course-cta-atomic-structure {\n            --navy: #1C244B;\n            --blue: #2563eb;\n            --body-text: #1f2937;\n            --grey-text: #667085;\n            --border: rgba(28, 36, 75, 0.14);\n            --shadow: 0 18px 45px rgba(28, 36, 75, 0.12);\n            --inner-shadow: 0 10px 26px rgba(28, 36, 75, 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src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/04\/edexcel-international-a-level-chemistry-topic-2-atomic-structure-periodic-table-course-banner.jpg\" alt=\"Edexcel International A Level Chemistry Topic 2 Atomic Structure and The Periodic Table course banner\">\n              <\/div>\n      \n            <\/a>\n      \n            <div class=\"ols-course-cta-content\">\n      \n              <div class=\"ols-course-cta-header-row\">\n      \n                <div class=\"ols-course-cta-kicker\">\n                  Complete Topic 2 Atomic Structure &amp; The Periodic Table Course\n                <\/div>\n      \n                <a class=\"ols-course-button ols-course-button-top\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/atomic-structure-and-periodic-table-edexcel-t2\/\">\n                  View Course\n                <\/a>\n      \n              <\/div>\n      \n              <h2>\n                Master Atomic Structure and The 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class=\"ols-mcq-screen\">\n                <section class=\"mcq-question-area\">\n                  <p class=\"mcq-question-lead\">Some successive ionisation energies for element X are shown.<\/p>\n      \n                  <table class=\"mcq-data-table\">\n                    <thead>\n                      <tr>\n                        <th>Ionisation energy<\/th>\n                        <th>Value \/ kJ mol<sup>\u22121<\/sup><\/th>\n                      <\/tr>\n                    <\/thead>\n                    <tbody>\n                      <tr><td>1st<\/td><td>738<\/td><\/tr>\n                      <tr><td>2nd<\/td><td>1451<\/td><\/tr>\n                      <tr><td>3rd<\/td><td>7733<\/td><\/tr>\n                      <tr><td>4th<\/td><td>10543<\/td><\/tr>\n                    <\/tbody>\n                  <\/table>\n      \n                  <p class=\"mcq-question-main\">Which formula is most likely for the fluoride of element X?<\/p>\n      \n                  <div class=\"mcq-options-wrap\">\n                    <div id=\"mcqWrongOption\" class=\"mcq-option-row\">\n                      <span class=\"mcq-radio\"><\/span>\n                      <span class=\"mcq-radio-ripple\"><\/span>\n                      <span class=\"mcq-option-label\">XF<\/span>\n      \n                      <span id=\"mcqSpecificFeedback\" class=\"mcq-specific-feedback\">\n                        <span id=\"mcqCrossIcon\" class=\"mcq-cross-icon\">\u00d7<\/span>\n                        <span class=\"mcq-specific-feedback-text\">\n                          <span id=\"mcqSpecificText\"><\/span><span id=\"mcqSpecificCursor\" class=\"cursor mcq-specific-cursor\" style=\"display:none;\"><\/span>\n                        <\/span>\n                      <\/span>\n                    <\/div>\n      \n                    <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span 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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>\n      <\/section>\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-international\/topic-2-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-international\/topic-2-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-international\/topic-2-atomic-structure-and-the-periodic-table\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/\">Identifying Compounds from Mass Spectra<\/a>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-attribution-card\">\n        <p><strong>Copyright notice:<\/strong> This revision page and its explanations are original OLS teaching resources written for Online Learning System by <strong>Dr. Mohammed Al-Fatah<\/strong>. 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