{"id":3991,"date":"2026-05-21T04:56:37","date_gmt":"2026-05-21T03:56:37","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-atomic-structure-and-the-periodic-table\/mass-spectrometry\/ram-calculations\/"},"modified":"2026-05-30T07:44:51","modified_gmt":"2026-05-30T06:44:51","slug":"ram-calculations","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\/ram-calculations\/","title":{"rendered":"RAM Calculations"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-ram-calculations-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: 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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 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-group\/\">Trends in a Group<\/a>\r\n          <\/li>\r\n        <\/ul>\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 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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/\">Edexcel International<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-atomic-structure-and-the-periodic-table\/\">Topic 2 Atomic Structure &amp; The Periodic Table<\/a> \/\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> \/\n        <span>RAM Calculations<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>RAM Calculations<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to calculating relative atomic mass from isotopic abundances, mass spectra and missing isotope data.<\/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        <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        View LinkedIn Profile\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>What Relative Atomic Mass Means<\/h2><\/div>\n        <p><strong>Relative atomic mass<\/strong>, A<sub>r<\/sub>, is the weighted mean mass of an atom of an element compared with one twelfth of the mass of a carbon-12 atom.<\/p>\n        <p>Most elements exist as a mixture of isotopes. This means the relative atomic mass is usually not a whole number, because it depends on both the <strong>relative isotopic masses<\/strong> and the <strong>relative abundances<\/strong> of those isotopes.<\/p>\n        <div class=\"ols-key-box\"><p><strong>Key idea:<\/strong> the isotope that is more abundant has a greater effect on the final A<sub>r<\/sub> value.<\/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>The Relative Atomic Mass Formula<\/h2><\/div>\n        <p>To calculate A<sub>r<\/sub>, multiply each isotopic mass by its abundance, add the results, then divide by the total abundance.<\/p>\n\n        <div class=\"ols-formula-box\">\n          <p>A<sub>r<\/sub> = \u03a3(isotopic mass \u00d7 abundance) \u00f7 \u03a3(abundance)<\/p>\n          <small>If percentage abundances are used, the total abundance is usually 100.<\/small>\n        <\/div>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Data type<\/th>\n                <th>How to divide<\/th>\n                <th>Typical exam wording<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Data type\">Percentage abundance<\/td>\n                <td data-label=\"How to divide\">Divide by 100<\/td>\n                <td data-label=\"Typical exam wording\">20.0% of atoms are boron-10 and 80.0% are boron-11<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Data type\">Relative abundance from a mass spectrum<\/td>\n                <td data-label=\"How to divide\">Divide by the sum of the peak abundances<\/td>\n                <td data-label=\"Typical exam wording\">The peaks have relative abundances of 114.0, 0.2 and 11.2<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\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\/Calculating-relative-atomic-mass-tutorial.webp\" alt=\"Worked tutorial showing how to calculate relative atomic mass from mass spectrum peak abundances\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>Mass spectrum peak heights act as relative abundances, so they must be included in the weighted mean calculation.<\/p>\n          <\/div>\n        <\/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>Calculating A<sub>r<\/sub> from Isotopic Abundances<\/h2><\/div>\n        <p>When the abundances are percentages, the calculation is straightforward because the total abundance is 100.<\/p>\n\n        <div class=\"ols-worked-grid\">\n          <div class=\"ols-worked-step\">\n            <h3>Example: boron<\/h3>\n            <p>20.0% of boron atoms have relative isotopic mass 10.0 and 80.0% have relative isotopic mass 11.0.<\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Step 1: multiply and add<\/h3>\n            <p>(20.0 \u00d7 10.0) + (80.0 \u00d7 11.0) = 200.0 + 880.0 = 1080.0<\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Step 2: divide by 100<\/h3>\n            <p>1080.0 \u00f7 100 = <strong>10.8<\/strong><\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\"><p><strong>Exam focus:<\/strong> do not simply average 10.0 and 11.0. The answer is closer to 11.0 because boron-11 is more abundant.<\/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>Calculating A<sub>r<\/sub> from a Mass Spectrum<\/h2><\/div>\n        <p>In a simple isotope mass spectrum, the <strong>x-axis<\/strong> gives the m\/z values. If the ions have a 1+ charge, these m\/z values can usually be treated as the relative isotopic masses.<\/p>\n        <p>The <strong>height of each peak<\/strong> shows the relative abundance of that isotope. Use these peak heights in the weighted mean calculation.<\/p>\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\/Mass-spectra-of-chlorine-isotopes.webp\" alt=\"Mass spectrum of chlorine showing peaks for chlorine-35 and chlorine-37 isotopes\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>The two chlorine peaks show that chlorine-35 is more abundant than chlorine-37, so the A<sub>r<\/sub> is closer to 35 than 37.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-worked-grid\">\n          <div class=\"ols-worked-step\">\n            <h3>Example: chlorine<\/h3>\n            <p>Chlorine has peaks at m\/z 35 and m\/z 37 with abundances of 75.5% and 24.5%.<\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Calculation<\/h3>\n            <p>A<sub>r<\/sub> = [(35 \u00d7 75.5) + (37 \u00d7 24.5)] \u00f7 100 = 35.49, so A<sub>r<\/sub> \u2248 <strong>35.5<\/strong>.<\/p>\n          <\/div>\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>When Abundances Are Not Percentages<\/h2><\/div>\n        <p>Some questions give relative abundances that do not add up to 100. In these cases, divide by the <strong>sum of the relative abundances<\/strong>, not by 100.<\/p>\n\n        <div class=\"ols-worked-grid\">\n          <div class=\"ols-worked-step\">\n            <h3>Example: neon spectrum<\/h3>\n            <p>Masses 20, 21 and 22 have relative abundances of 114.0, 0.2 and 11.2.<\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Step 1: multiply and add<\/h3>\n            <p>(20 \u00d7 114.0) + (21 \u00d7 0.2) + (22 \u00d7 11.2) = 2530.6<\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Step 2: divide by total abundance<\/h3>\n            <p>Total abundance = 114.0 + 0.2 + 11.2 = 125.4<\/p>\n            <p>2530.6 \u00f7 125.4 = <strong>20.2<\/strong><\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\"><p><strong>Common mistake:<\/strong> only divide by 100 when the abundances are percentages that total 100.<\/p><\/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>Finding Missing Isotope Data<\/h2><\/div>\n        <p>Some questions give the A<sub>r<\/sub> and some isotope data, then ask for the abundance or isotopic mass of a missing isotope. Use the same weighted mean equation, but rearrange it.<\/p>\n\n        <div class=\"ols-worked-grid\">\n          <div class=\"ols-worked-step\">\n            <h3>Example: silicon abundance<\/h3>\n            <p>Silicon has three isotopes. 92.23% is <sup>28<\/sup>Si and 4.67% is <sup>29<\/sup>Si. The remaining isotope has abundance:<\/p>\n            <p>100.00 \u2212 92.23 \u2212 4.67 = <strong>3.10%<\/strong><\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Example: silicon mass<\/h3>\n            <p>If A<sub>r<\/sub> = 28.1 and the final isotope has mass X:<\/p>\n            <p>28.1 = [(28 \u00d7 92.23) + (29 \u00d7 4.67) + (X \u00d7 3.10)] \u00f7 100<\/p>\n          <\/div>\n          <div class=\"ols-worked-step\">\n            <h3>Rearranged result<\/h3>\n            <p>2810 = 2717.87 + 3.10X<\/p>\n            <p>92.13 = 3.10X<\/p>\n            <p>X = 29.7, so the isotope is treated as <strong><sup>30<\/sup>Si<\/strong>.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\"><p><strong>Exam focus:<\/strong> isotopic mass numbers are normally whole numbers, so a calculated value close to 30 represents silicon-30.<\/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 are useful for short calculation questions and explanations linked to mass spectra.<\/p>\n\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\"><h3>Use peak height as abundance<\/h3><p>In simple mass spectra, the peak height gives the relative abundance of that isotope.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>Check the total abundance<\/h3><p>If the data are percentages, divide by 100. If they are relative abundances, divide by their total.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>Use m\/z carefully<\/h3><p>If the charge is 1+, the m\/z value is usually treated as the relative isotopic mass. If the charge is not 1+, the mass-to-charge ratio must be considered directly.<\/p><\/div>\n          <div class=\"ols-rule-item\"><h3>Round only at the end<\/h3><p>Keep extra figures during the calculation, then round to the number of decimal places requested in the question.<\/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 the calculation method before moving on to exam-style questions.<\/p>\n\n        <div class=\"ols-h5p-grid\">\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-242\" class=\"h5p-iframe\" data-content-id=\"242\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"RAMCalculations.1 Drag: Relative Atomic Mass Key Concepts\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-243\" class=\"h5p-iframe\" data-content-id=\"243\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"RAMCalculations.2 MCQ: RAM from Isotopic Abundance\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-244\" class=\"h5p-iframe\" data-content-id=\"244\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"RAMCalculations.3 MCQ: RAM from a Chlorine Mass Spectrum\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-245\" class=\"h5p-iframe\" data-content-id=\"245\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"RAMCalculations.4 MCQ: Missing Isotope Data\"><\/iframe><\/div><\/div>\n          <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-338\" class=\"h5p-iframe\" data-content-id=\"338\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Relative Atomic Masses: Isotopic Abundance Dialog Cards\"><\/iframe><\/div><\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-quicksnap-card\">\n        <h2>QuickSnap Summary<\/h2>\n        <p>A<sub>r<\/sub> is a weighted mean, so both isotopic mass and abundance matter.<\/p>\n\n        <div class=\"ols-snap-list\">\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">1<\/div><p>Multiply each isotope mass by its abundance.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">2<\/div><p>Add all of the mass \u00d7 abundance values.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">3<\/div><p>Divide by the total abundance. For percentages, this is normally 100.<\/p><\/div>\n          <div class=\"ols-snap-item\"><div class=\"ols-snap-number\">4<\/div><p>For a mass spectrum, use the m\/z values as isotope masses when the ions are 1+ and use peak heights as relative abundances.<\/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, 0.08);\n      \n            width: 100%;\n            margin: 30px 0 24px;\n            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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\"\n                  alt=\"Edexcel International A Level Chemistry Topic 2 Atomic Structure and The Periodic Table course banner\"\n                >\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 &#038; 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 Periodic Table for Edexcel International A Level Chemistry\n              <\/h2>\n      \n            <\/div>\n      \n          <\/div>\n      \n          <div class=\"ols-course-cta-intro-stats\">\n      \n            <p class=\"ols-course-cta-intro\">\n              Continue from these free revision notes into the full Topic 2 Atomic Structure and The Periodic Table course, with guided video teaching, diagnostic MCQ practice, teacher-marked short-answer questions and a specification assignment with a personalised progress report.\n            <\/p>\n      \n            <div class=\"ols-course-cta-stats\">\n      \n              <div class=\"ols-course-stat\">\n                <span>Guided learning<\/span>\n                <strong>18 hours<\/strong>\n              <\/div>\n      \n              <div class=\"ols-course-stat\">\n                <span>Video lessons<\/span>\n                <strong>369 mins<\/strong>\n              <\/div>\n      \n        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id=\"videoTitleText\"><\/span><span id=\"videoTitleCursor\" class=\"ols-title-cursor\"><\/span>\n                <\/h1>\n              <\/div>\n            <\/div>\n      \n            <section id=\"videoScene\" class=\"ols-video-scene\">\n              <div class=\"ols-video-scale-wrap\">\n                <div class=\"ols-video-card\">\n                  <video\n                    id=\"lessonVideo\"\n                    src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Virtual-Lesson.mp4\"\n                    muted\n                    playsinline\n                    preload=\"auto\">\n                  <\/video>\n                <\/div>\n              <\/div>\n            <\/section>\n          <\/div>\n        <\/section>\n      \n        <section id=\"sceneMcq\" class=\"ols-scene\">\n          <div class=\"ols-mcq-stage\">\n            <div id=\"mcqIntroScreen\" class=\"ols-mcq-intro-screen\">\n              <div class=\"ols-mcq-intro-title-wrap\">\n                <h1 class=\"ols-mcq-intro-title\">\n                  <span id=\"mcqIntroTitleText\"><\/span><span id=\"mcqIntroTitleCursor\" class=\"ols-title-cursor\"><\/span>\n                <\/h1>\n              <\/div>\n            <\/div>\n      \n            <div class=\"ols-mcq-scale-wrap\">\n              <main id=\"mcqScreen\" 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 class=\"mcq-option-label\">XF<sub>2<\/sub><\/span><\/div>\n                    <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span class=\"mcq-option-label\">XF<sub>3<\/sub><\/span><\/div>\n                    <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span class=\"mcq-option-label\">XF<sub>4<\/sub><\/span><\/div>\n                  <\/div>\n      \n                  <button id=\"mcqSubmitButton\" class=\"mcq-submit-button\">Submit answer<\/button>\n                <\/section>\n      \n                <section id=\"mcqGeneralFeedback\" class=\"mcq-general-feedback\">\n                  <span id=\"mcqGeneralText\"><\/span><span id=\"mcqGeneralCursor\" class=\"cursor mcq-general-cursor\" style=\"display:none;\"><\/span>\n                <\/section>\n              <\/main>\n            <\/div>\n          <\/div>\n        <\/section>\n      \n        <section id=\"sceneSaq\" class=\"ols-scene\">\n          <div class=\"ols-saq-stage\">\n            <div id=\"saqIntro\" class=\"ols-saq-intro\">\n              <div class=\"ols-saq-intro-title-wrap\">\n                <h1 class=\"ols-saq-intro-title\">\n                  <span id=\"saqIntroTitleText\"><\/span><span id=\"saqIntroTitleCursor\" class=\"ols-title-cursor\"><\/span>\n                <\/h1>\n              <\/div>\n            <\/div>\n      \n            <div class=\"ols-saq-scale-wrap\">\n              <main id=\"saqScreen\" class=\"ols-saq-screen\">\n                <section class=\"saq-question-area\">\n                  <div class=\"saq-question-text\">\n                    <strong>(ii)<\/strong>&nbsp;&nbsp; First ionisation energy generally increases across Period 3.<br>\n                    Explain this trend in terms of nuclear charge, shielding and atomic radius.\n                  <\/div>\n      \n                  <div class=\"saq-student-box\">\n                    <span id=\"saqStudentText\"><\/span><span id=\"saqStudentCursor\" class=\"cursor\"><\/span>\n                  <\/div>\n                <\/section>\n      \n                <section id=\"saqTeacherFeedback\" class=\"saq-teacher-feedback\">\n                  <span id=\"saqTeacherText\"><\/span><span id=\"saqTeacherCursor\" class=\"cursor saq-teacher-cursor\" style=\"display:none;\"><\/span>\n                <\/section>\n              <\/main>\n            <\/div>\n          <\/div>\n        <\/section>\n      \n      <\/div>\n      \n      <script>\n      (function(){\n        const nativeSetTimeout=window.setTimeout.bind(window);\n        const 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a whole number?<\/h3><p>It is a weighted mean of the masses of different isotopes, using their relative abundances.<\/p><\/div>\n          <div class=\"ols-faq-item\"><h3>How do you calculate A<sub>r<\/sub> from percentage abundances?<\/h3><p>Multiply each isotopic mass by its percentage abundance, add the results, then divide by 100.<\/p><\/div>\n          <div class=\"ols-faq-item\"><h3>How do you calculate A<sub>r<\/sub> from mass spectrum peaks?<\/h3><p>Use the m\/z values as isotope masses for 1+ ions, use the peak heights as relative abundances, then divide by the sum of the peak heights.<\/p><\/div>\n          <div class=\"ols-faq-item\"><h3>Why is chlorine's A<sub>r<\/sub> about 35.5?<\/h3><p>Chlorine-35 is more abundant than chlorine-37, so the weighted mean lies closer to 35 than to 37.<\/p><\/div>\n          <div class=\"ols-faq-item\"><h3>What is the most common RAM calculation mistake?<\/h3><p>The most common mistake is dividing by 100 when the abundances are relative peak heights that do not total 100.<\/p><\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Continue with the linked Topic 2 revision pages to connect RAM calculations with mass spectra, isotopes and ionisation energy.<\/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\/predicting-diatomic-mass-spectra\/\">Predicting Diatomic Mass Spectra<\/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\/atomic-structure\/\">Atomic Structure<\/a>\n        <\/div>\n      <\/section>\n    <!-- OLS Author Copyright Footprint \/ Attribution Card -->\n      <section class=\"ols-attribution-card\">\n        <style>\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 * {\n            box-sizing: border-box;\n          }\n\n          .ols-attribution-card p {\n            margin: 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      {\n            \"@type\": \"Question\",\n            \"name\": \"Why is chlorine's Ar about 35.5?\",\n            \"acceptedAnswer\": {\n              \"@type\": \"Answer\",\n              \"text\": \"Chlorine-35 is more abundant than chlorine-37, so the weighted mean lies closer to 35 than to 37.\"\n            }\n          },\n          {\n            \"@type\": \"Question\",\n            \"name\": \"What is the most common RAM calculation mistake?\",\n            \"acceptedAnswer\": {\n              \"@type\": \"Answer\",\n              \"text\": \"The most common mistake is dividing by 100 when the abundances are relative peak heights that do not total 100.\"\n            }\n          }\n        ]\n      }\n    ]\n  }\n  <\/script>\n<\/section>\n","protected":false},"excerpt":{"rendered":"<p>Revision Notes \/ A Level Chemistry \/ Edexcel International \/ Topic 2 Atomic Structure &amp; The Periodic Table \/ Mass Spectrometry \/ RAM Calculations RAM Calculations A concise revision guide to calculating relative atomic mass from isotopic abundances, mass spectra and missing isotope data. Exam board: Edexcel International Topic 2: Atomic Structure &amp; The Periodic [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":3987,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-3991","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/3991","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=3991"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/3991\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/3987"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=3991"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}