{"id":4513,"date":"2026-05-28T06:03:42","date_gmt":"2026-05-28T05:03:42","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/atomic-structure\/"},"modified":"2026-05-30T07:09:35","modified_gmt":"2026-05-30T06:09:35","slug":"atomic-structure","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/atomic-structure\/","title":{"rendered":"Atomic Structure"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-atomic-structure-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      --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; 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font-size: 28px; line-height: 1; font-weight: 700; cursor: pointer; box-shadow: 0 16px 34px rgba(0, 0, 0, 0.28); display: flex; align-items: center; justify-content: center; transition: transform 0.2s ease, background 0.2s ease, color 0.2s ease; }\n    .ols-image-lightbox-close:hover { transform: scale(1.08); background: var(--blue); color: #ffffff; }\n    .ols-zoom-card img.ols-lightbox-target { cursor: zoom-in !important; }\n    @media (max-width: 760px) { .ols-image-lightbox { padding: 16px; } .ols-image-lightbox-inner { width: 100%; max-height: 88vh; } .ols-image-lightbox-img { max-height: 88vh; border-radius: 16px; } .ols-image-lightbox-close { top: 10px; right: 10px; width: 42px; height: 42px; font-size: 26px; } }\n\n    @media (max-width: 1050px) {\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      .ols-title-card, .ols-note-card, .ols-h5p-card, .ols-related-card, .ols-faq-card, .ols-unlock { padding: 24px 18px; 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display: block; margin-bottom: 6px; font-size: 13px; font-weight: 700; color: var(--blue); }\n      .ols-author { align-items: flex-start; padding: 22px 18px; border-radius: 22px; }\n      .ols-author-avatar-img { width: 72px; height: 72px; }\n      .ols-author-title { font-size: 24px; }\n      .ols-author-description { font-size: 15px; }\n      .ols-left-numbers { font-size: 26px; }\n      .ols-symbol-core { font-size: 52px; }\n      .ols-symbol-labels { font-size: 13px; }\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 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        <span>Atomic Structure<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Atomic Structure<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to subatomic particles, atomic number, mass number, nuclide notation, isotopes, relative isotopic mass and relative formula mass for Edexcel A Level Chemistry.<\/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\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\">\n          <div class=\"ols-note-icon\">1<\/div>\n          <h2>Subatomic Particles<\/h2>\n        <\/div>\n\n        <p>Atoms are made from three main subatomic particles: <strong>protons<\/strong>, <strong>neutrons<\/strong> and <strong>electrons<\/strong>.<\/p>\n        <p>Protons and neutrons are found in the <strong>nucleus<\/strong>, while electrons occupy regions of space around the nucleus. Protons and neutrons are also called <strong>nucleons<\/strong>.<\/p>\n        <p>Almost all of the mass of an atom is concentrated in the nucleus. The rest of the atom is mostly empty space.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Particle<\/th>\n                <th>Position<\/th>\n                <th>Relative mass<\/th>\n                <th>Relative charge<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Particle\">Proton<\/td>\n                <td data-label=\"Position\">Nucleus<\/td>\n                <td data-label=\"Relative mass\">1<\/td>\n                <td data-label=\"Relative charge\">+1<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Particle\">Neutron<\/td>\n                <td data-label=\"Position\">Nucleus<\/td>\n                <td data-label=\"Relative mass\">1<\/td>\n                <td data-label=\"Relative charge\">0<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Particle\">Electron<\/td>\n                <td data-label=\"Position\">Orbitals or shells around the nucleus<\/td>\n                <td data-label=\"Relative mass\">1\/1840<\/td>\n                <td data-label=\"Relative charge\">-1<\/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\/Bohr-model-of-an-atom-diagram.webp\" alt=\"Bohr model diagram showing the nucleus and electron shells of an atom\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>This simplified Bohr model shows the nucleus at the centre with electrons arranged in shells around it.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">2<\/div>\n          <h2>Atomic Number and Mass Number<\/h2>\n        <\/div>\n\n        <p>The <strong>atomic number<\/strong>, symbol <strong>Z<\/strong>, is the number of protons in the nucleus of an atom.<\/p>\n        <p>The <strong>mass number<\/strong>, symbol <strong>A<\/strong>, is the total number of protons and neutrons in the atom.<\/p>\n        <p>For a neutral atom, the number of electrons is equal to the number of protons.<\/p>\n\n        <div class=\"ols-notation-card\">\n          <div class=\"ols-nuclide-symbol\" aria-label=\"Lithium nuclide notation showing mass number 7 and atomic number 3\">\n            <div class=\"ols-left-numbers\"><span>7<\/span><span>3<\/span><\/div>\n            <div class=\"ols-symbol-core\">Li<\/div>\n            <div class=\"ols-symbol-labels\"><span>mass number, A<\/span><span>atomic number, Z<\/span><\/div>\n          <\/div>\n          <div class=\"ols-formula-strip\">number of neutrons = A &#8211; Z<\/div>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Example:<\/strong> In <strong><sup>7<\/sup><sub>3<\/sub>Li<\/strong>, the atom has 3 protons and 7 &#8211; 3 = 4 neutrons. A neutral lithium atom also has 3 electrons.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>Isotopes<\/h2>\n        <\/div>\n\n        <p><strong>Isotopes<\/strong> are atoms with the same number of protons but different numbers of neutrons.<\/p>\n        <p>Because isotopes of the same element have the same number of protons, they have the same atomic number. Their mass numbers are different because the number of neutrons is different.<\/p>\n        <p>Isotopes normally have very similar chemical properties because they have the same electronic structure. They may have slightly different physical properties because their masses are different.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Isotope<\/th>\n                <th>Symbol<\/th>\n                <th>Number of protons<\/th>\n                <th>Number of neutrons<\/th>\n                <th>Number of electrons in a neutral atom<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Isotope\">chlorine-35<\/td>\n                <td data-label=\"Symbol\"><sup>35<\/sup><sub>17<\/sub>Cl<\/td>\n                <td data-label=\"Number of protons\">17<\/td>\n                <td data-label=\"Number of neutrons\">18<\/td>\n                <td data-label=\"Number of electrons in a neutral atom\">17<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Isotope\">chlorine-37<\/td>\n                <td data-label=\"Symbol\"><sup>37<\/sup><sub>17<\/sub>Cl<\/td>\n                <td data-label=\"Number of protons\">17<\/td>\n                <td data-label=\"Number of neutrons\">20<\/td>\n                <td data-label=\"Number of electrons in a neutral atom\">17<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> Isotopes differ in neutrons, not protons. If the number of protons changes, it is a different element.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Relative Isotopic Mass<\/h2>\n        <\/div>\n\n        <p><strong>Relative isotopic mass<\/strong> is the mass of one atom of an isotope compared with one twelfth of the mass of one atom of carbon-12.<\/p>\n        <p>Carbon-12 is used as the standard because one atom of carbon-12 is defined as exactly 12 atomic mass units.<\/p>\n        <p>This relative scale avoids using extremely small masses in kilograms when comparing atoms and isotopes.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Term<\/th>\n                <th>Meaning<\/th>\n                <th>Exam wording to use<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Term\">Atomic mass unit<\/td>\n                <td data-label=\"Meaning\">One twelfth of the mass of one atom of carbon-12.<\/td>\n                <td data-label=\"Exam wording to use\">Use <strong>1\/12<\/strong> and <strong>carbon-12<\/strong>.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Term\">Relative isotopic mass<\/td>\n                <td data-label=\"Meaning\">The mass of one atom of an isotope on the carbon-12 scale.<\/td>\n                <td data-label=\"Exam wording to use\">Refer to <strong>one atom<\/strong> of an isotope.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Term\">Relative atomic mass<\/td>\n                <td data-label=\"Meaning\">The weighted mean mass of atoms of an element compared with 1\/12 of carbon-12.<\/td>\n                <td data-label=\"Exam wording to use\">This is covered in more depth in RAM calculations.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>Relative Molecular Mass and Relative Formula Mass<\/h2>\n        <\/div>\n\n        <p>The <strong>relative formula mass<\/strong>, M<sub>r<\/sub>, is found by adding together the relative atomic masses of all the atoms shown in a formula.<\/p>\n        <p>The term <strong>relative molecular mass<\/strong>, sometimes written RMM, should only be used for substances that exist as molecules. <strong>Relative formula mass<\/strong> is the safer term because it applies to molecular substances, ionic compounds and giant structures. The specification states that the term <strong>relative formula mass<\/strong> should be used for compounds with giant structures.<\/p>\n\n        <div class=\"ols-definition-box\"><p><strong>Relative formula mass, M<sub>r<\/sub>:<\/strong> the sum of the relative atomic masses of all atoms in the formula of a substance.<\/p><\/div>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Substance<\/th>\n                <th>Formula<\/th>\n                <th>Calculation<\/th>\n                <th>M<sub>r<\/sub><\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Substance\">Carbon dioxide<\/td>\n                <td data-label=\"Formula\">CO<sub>2<\/sub><\/td>\n                <td data-label=\"Calculation\">12.0 + (2 \u00d7 16.0)<\/td>\n                <td data-label=\"Mr\">44.0<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Substance\">Calcium carbonate<\/td>\n                <td data-label=\"Formula\">CaCO<sub>3<\/sub><\/td>\n                <td data-label=\"Calculation\">40.1 + 12.0 + (3 \u00d7 16.0)<\/td>\n                <td data-label=\"Mr\">100.1<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Substance\">Magnesium nitrate<\/td>\n                <td data-label=\"Formula\">Mg(NO<sub>3<\/sub>)<sub>2<\/sub><\/td>\n                <td data-label=\"Calculation\">24.3 + 2(14.0 + 3 \u00d7 16.0)<\/td>\n                <td data-label=\"Mr\">148.3<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\"><p><strong>Exam focus:<\/strong> brackets multiply everything inside them. In Mg(NO<sub>3<\/sub>)<sub>2<\/sub>, there are two nitrogen atoms and six oxygen atoms.<\/p><\/div>\n      <\/article>\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\/05\/How-to-calculate-relative-formula-masses.webp\" alt=\"How to calculate relative formula masses using relative atomic masses\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>Relative formula mass is calculated by counting each atom in the formula and adding the correct relative atomic masses.<\/p>\n        <\/div>\n      <\/div>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">6<\/div>\n          <h2>Common Exam Points<\/h2>\n        <\/div>\n\n        <p>Atomic structure questions often reward precise definitions and careful counting. The most important terms are <strong>atomic number<\/strong>, <strong>mass number<\/strong>, <strong>isotope<\/strong>, <strong>neutron number<\/strong> and <strong>relative isotopic mass<\/strong>.<\/p>\n\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\">\n            <h3>Do not confuse atomic number and mass number<\/h3>\n            <p>Atomic number is the number of protons. Mass number is the total number of protons and neutrons.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Use A &#8211; Z for neutrons<\/h3>\n            <p>The number of neutrons is found by subtracting the atomic number from the mass number.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Neutral atoms have equal protons and electrons<\/h3>\n            <p>If the atom is neutral, the positive charge from protons is balanced by the negative charge from electrons.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Isotopes have the same electronic structure<\/h3>\n            <p>This explains why isotopes of the same element have similar chemical properties.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n\n      <section class=\"ols-h5p-card\">\n        <h2>Check Your Understanding<\/h2>\n        <p>Use these short activities to check subatomic particles, nuclide notation, isotopes and relative isotopic mass before moving on.<\/p>\n\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-337\" class=\"h5p-iframe\" data-content-id=\"337\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Atomic Structure: Write Isotope and Ion Symbols\"><\/iframe><\/div><\/div>\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-232\" class=\"h5p-iframe\" data-content-id=\"232\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"AtomicStructure.1 Drag: Atomic Structure Key Concepts\"><\/iframe><\/div><\/div>\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-233\" class=\"h5p-iframe\" data-content-id=\"233\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"AtomicStructure.2 MCQ: Subatomic Particle Charges\"><\/iframe><\/div><\/div>\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-234\" class=\"h5p-iframe\" data-content-id=\"234\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"AtomicStructure.3 MCQ: Number of Neutrons\"><\/iframe><\/div><\/div>\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-235\" class=\"h5p-iframe\" data-content-id=\"235\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"AtomicStructure.4 MCQ: Isotopes and Chemical Properties\"><\/iframe><\/div><\/div>\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-304\" class=\"h5p-iframe\" data-content-id=\"304\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Property that determines order of elements in the Periodic Table\"><\/iframe><\/div><\/div>\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-305\" class=\"h5p-iframe\" data-content-id=\"305\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Ion that is not isoelectronic with the others\"><\/iframe><\/div><\/div>\n        <div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-336\" class=\"h5p-iframe\" data-content-id=\"336\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Atomic Structure: Protons, Neutrons and Electrons\"><\/iframe><\/div><\/div>\n      <\/section>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">\u2713<\/div>\n          <h2>QuickSnap<\/h2>\n        <\/div>\n\n        <p>For this page, the essential idea is that the nucleus contains protons and neutrons, while electrons occupy regions around the nucleus. Atomic number counts protons, mass number counts protons plus neutrons, and isotopes have the same number of protons but different numbers of neutrons.<\/p>\n\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\">\n            <h3>Subatomic particles<\/h3>\n            <p>Protons have charge +1, neutrons have charge 0, and electrons have charge -1. Protons and neutrons have relative mass 1, while electrons have a much smaller relative mass of about 1\/1840.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Atomic number and mass number<\/h3>\n            <p>Atomic number, Z, gives the number of protons. Mass number, A, gives the number of protons plus neutrons.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Isotopes<\/h3>\n            <p>Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Carbon-12 scale<\/h3>\n            <p>Relative isotopic mass compares one atom of an isotope with one twelfth of the mass of one atom of carbon-12.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\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            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page\">\n      \n              <div class=\"ols-course-cta-image\">\n                <img decoding=\"async\"\n                  src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/T1-Atomic-Structure-and-The-Periodic-Table.jpg\"\n                  alt=\"Edexcel A Level Chemistry Topic 1 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 1 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-the-periodic-table-topic-1\/\">\n                  View Course\n                <\/a>\n      \n              <\/div>\n      \n              <h2>\n                Master Atomic Structure and The Periodic Table for Edexcel 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 1 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              <div class=\"ols-course-stat\">\n                <span>MCQ practice<\/span>\n                <strong>86 marks<\/strong>\n              <\/div>\n      \n              <div class=\"ols-course-stat\">\n                <span>SAQ practice<\/span>\n                <strong>215 marks<\/strong>\n              <\/div>\n      \n            <\/div>\n      \n          <\/div>\n      \n          <div class=\"ols-course-cta-features\">\n      \n            <div class=\"ols-course-feature\">\n              <h3>Guided video teaching<\/h3>\n              <p>\n                Learn atomic structure, isotopes, mass spectrometry, ionisation energy, electron configuration and periodic trends through structured video lessons with worked examples and walkthroughs.\n              <\/p>\n            <\/div>\n      \n            <div class=\"ols-course-feature\">\n              <h3>Instant MCQ feedback<\/h3>\n              <p>\n                Auto-marked MCQ quizzes provide immediate diagnostic feedback for every answer choice.\n              <\/p>\n            <\/div>\n      \n            <div class=\"ols-course-feature\">\n              <h3>Teacher-marked SAQs<\/h3>\n              <p>\n                Submit written exam responses and receive chemistry specialist feedback with improvement guidance.\n              <\/p>\n            <\/div>\n      \n            <div class=\"ols-course-feature\">\n              <h3>Progress tracking<\/h3>\n              <p>\n                Identify strengths and weaknesses across atomic structure, isotopes, mass spectrometry, ionisation energies, electron configuration and periodic trends with targeted reporting.\n              <\/p>\n            <\/div>\n      \n          <\/div>\n      \n          <div class=\"ols-course-animation-wrap\">\n      \n            <h3 class=\"ols-course-animation-title\">\n              See how the course works\n            <\/h3>\n      \n            <div class=\"ols-animation-frame-shell\">\n              <iframe\n                id=\"olsCourseAnimationFrame002\"\n                title=\"OLS course preview animation\"\n                loading=\"lazy\"\n                referrerpolicy=\"no-referrer\">\n              <\/iframe>\n      \n              <button\n                class=\"ols-animation-start-overlay\"\n                id=\"olsCourseAnimationStart002\"\n                type=\"button\"\n                aria-label=\"Play OLS course preview animation\">\n                <span class=\"ols-animation-start-content\">\n                  <span class=\"ols-animation-play-circle\" aria-hidden=\"true\">\n                    <span class=\"ols-animation-play-icon\"><\/span>\n                  <\/span>\n                  <span class=\"ols-animation-start-text\">\n                    Play course preview animation\n                  <\/span>\n                <\/span>\n              <\/button>\n      \n              <button\n                class=\"ols-animation-pause-button\"\n                id=\"olsCourseAnimationPause002\"\n                type=\"button\"\n                aria-label=\"Pause course preview animation\">\n                Pause\n              <\/button>\n            <\/div>\n      \n            <p class=\"ols-course-video-status\">\n              Click play to start the course preview animation.\n            <\/p>\n      \n          <\/div>\n      \n          <div class=\"ols-course-cta-bottom\">\n      \n            <a class=\"ols-course-button\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/atomic-structure-and-the-periodic-table-topic-1\/\">\n              View Atomic Structure &#038; The Periodic Table Topic 1 Course\n            <\/a>\n      \n          <\/div>\n      \n        <\/div>\n      \n        <template id=\"olsCourseAnimationTemplate002\">\n<!DOCTYPE html>\n<html lang=\"en\">\n<head>\n<meta charset=\"UTF-8\" \/>\n<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\" \/>\n<title>OLS Combined Promo Animation<\/title>\n\n<style>\n*{\n  box-sizing:border-box;\n}\n\n:root{\n  --ols-video-screen-w:1180;\n  --ols-video-screen-h:664;\n  --ols-video-screen-scale:1;\n\n  --ols-mcq-screen-w:1360;\n  --ols-mcq-screen-h:1130;\n  --ols-mcq-screen-scale:1;\n\n  --ols-saq-screen-w:1360;\n  --ols-saq-screen-h:965;\n  --ols-saq-screen-scale:1;\n}\n\nhtml,\nbody{\n  width:100%;\n  height:100%;\n}\n\nbody{\n  margin:0;\n  overflow:hidden;\n  font-family:Poppins,Arial,sans-serif;\n  background:#e9efff;\n}\n\n\/* ============================================================\n   GLOBAL SCENE SYSTEM\n============================================================ *\/\n\n.ols-combined-stage{\n  position:relative;\n  width:100vw;\n  height:100vh;\n  overflow:hidden;\n\n  background:\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\n}\n\n.ols-scene{\n  position:absolute;\n  inset:0;\n\n  width:100vw;\n  height:100vh;\n\n  opacity:0;\n  visibility:hidden;\n  pointer-events:none;\n}\n\n.ols-scene.active{\n  opacity:1;\n  visibility:visible;\n  pointer-events:auto;\n}\n\n.ols-scene.fade-out{\n  animation:olsSceneFadeOut 0.85s ease forwards;\n}\n\n@keyframes olsSceneFadeOut{\n  to{\n    opacity:0;\n    visibility:hidden;\n  }\n}\n\n.ols-title-cursor{\n  display:inline-block;\n\n  width:5px;\n  height:0.85em;\n\n  background:#1C244B;\n\n  margin-left:8px;\n\n  transform:translateY(8px);\n\n  animation:olsBlink 0.8s infinite;\n}\n\n.cursor{\n  display:inline-block;\n\n  width:3px;\n  height:28px;\n\n  background:#1c244b;\n\n  margin-left:3px;\n\n  transform:translateY(5px);\n\n  animation:olsBlink 0.8s infinite;\n}\n\n@keyframes olsBlink{\n  0%,45%{\n    opacity:1;\n  }\n  46%,100%{\n    opacity:0;\n  }\n}\n\n.ols-combined-stage.ols-animation-paused *,\n.ols-combined-stage.ols-animation-paused *::before,\n.ols-combined-stage.ols-animation-paused *::after{\n  animation-play-state:paused !important;\n}\n\n\/* ============================================================\n   1. VIRTUAL LESSON PROMO\n============================================================ *\/\n\n.ols-video-stage{\n  width:100vw;\n  height:100vh;\n\n  display:flex;\n  justify-content:center;\n  align-items:center;\n\n  padding:0;\n  overflow:hidden;\n\n  background:\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\n}\n\n.ols-video-title-screen{\n  position:absolute;\n  inset:0;\n  z-index:20;\n\n  display:flex;\n  justify-content:center;\n  align-items:center;\n\n  background:\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\n\n  opacity:1;\n  visibility:visible;\n  pointer-events:none;\n}\n\n.ols-video-title-screen.hide{\n  animation:olsVideoTitleFadeOut 0.85s ease forwards;\n}\n\n@keyframes olsVideoTitleFadeOut{\n  to{\n    opacity:0;\n    visibility:hidden;\n  }\n}\n\n.ols-video-title-wrap{\n  max-width:1250px;\n  padding:0 34px;\n  text-align:center;\n}\n\n.ols-video-title{\n  margin:0;\n\n  font-family:Poppins,Arial,sans-serif;\n\n  font-size:clamp(52px,8vw,124px);\n  font-weight:600;\n  line-height:1.08;\n\n  color:#1C244B;\n\n  text-shadow:-9px 0 9px rgba(28,36,75,0.16);\n\n  letter-spacing:-0.045em;\n}\n\n#videoTitleText{\n  white-space:pre-wrap;\n}\n\n.ols-video-scene{\n  width:100%;\n  height:100%;\n\n  display:flex;\n  justify-content:center;\n  align-items:center;\n\n  opacity:0;\n  visibility:hidden;\n}\n\n.ols-video-scene.show{\n  visibility:visible;\n  animation:olsVideoSceneIn 1s ease forwards;\n}\n\n@keyframes olsVideoSceneIn{\n  to{\n    opacity:1;\n  }\n}\n\n.ols-video-scale-wrap{\n  width:calc(var(--ols-video-screen-w) * 1px);\n  height:calc(var(--ols-video-screen-h) * 1px);\n\n  transform:scale(var(--ols-video-screen-scale));\n  transform-origin:center center;\n\n  display:flex;\n  justify-content:center;\n  align-items:center;\n}\n\n.ols-video-card{\n  width:1180px;\n  height:664px;\n\n  border-radius:28px;\n  overflow:hidden;\n\n  background:#1C244B;\n\n  box-shadow:\n    0 28px 80px rgba(28,36,75,0.28);\n\n  transform:translateY(24px) scale(0.96);\n  opacity:0;\n}\n\n.ols-video-scene.show .ols-video-card{\n  animation:olsVideoCardIn 1s cubic-bezier(.18,.89,.32,1.12) forwards;\n  animation-delay:0.2s;\n}\n\n@keyframes olsVideoCardIn{\n  to{\n    transform:translateY(0) scale(1);\n    opacity:1;\n  }\n}\n\n.ols-video-card video{\n  display:block;\n  width:100%;\n  height:100%;\n\n  aspect-ratio:16 \/ 9;\n  object-fit:cover;\n\n  border:0;\n}\n\n\/* ============================================================\n   2. MULTIPLE CHOICE FEEDBACK\n============================================================ *\/\n\n.ols-mcq-stage{\n  width:100vw;\n  height:100vh;\n\n  display:flex;\n  justify-content:center;\n  align-items:center;\n\n  padding:0;\n  overflow:hidden;\n\n  background:\n    radial-gradient(circle at top left,rgba(70,127,247,0.16),transparent 34%),\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\n}\n\n.ols-mcq-intro-screen{\n  position:absolute;\n  inset:0;\n  z-index:50;\n\n  display:flex;\n  justify-content:center;\n  align-items:center;\n\n  background:\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\n\n  opacity:1;\n  visibility:visible;\n  pointer-events:none;\n}\n\n.ols-mcq-intro-screen.hide{\n  animation:olsMcqIntroFadeOut 0.85s ease forwards;\n}\n\n@keyframes olsMcqIntroFadeOut{\n  to{\n    opacity:0;\n    visibility:hidden;\n  }\n}\n\n.ols-mcq-intro-title-wrap{\n  max-width:1250px;\n  padding:0 34px;\n  text-align:center;\n}\n\n.ols-mcq-intro-title{\n  margin:0;\n\n  font-family:Poppins,Arial,sans-serif;\n\n  font-size:clamp(52px,8vw,124px);\n  font-weight:600;\n  line-height:1.08;\n\n  color:#1C244B;\n\n  text-shadow:-9px 0 9px rgba(28,36,75,0.16);\n\n  letter-spacing:-0.045em;\n}\n\n#mcqIntroTitleText{\n  white-space:pre-wrap;\n}\n\n.ols-mcq-scale-wrap{\n  width:calc(var(--ols-mcq-screen-w) * 1px);\n  height:calc(var(--ols-mcq-screen-h) * 1px);\n\n  transform:scale(var(--ols-mcq-screen-scale));\n  transform-origin:center center;\n\n  display:flex;\n  justify-content:center;\n  align-items:flex-start;\n}\n\n.ols-mcq-screen{\n  width:1360px;\n  height:1130px;\n\n  border-radius:22px;\n  overflow:hidden;\n\n  background:#eaf0ff;\n\n  box-shadow:\n    0 26px 70px rgba(28,36,75,0.22);\n\n  opacity:0;\n  transform:translateY(24px) scale(0.96);\n}\n\n.ols-mcq-screen.show{\n  animation:olsMcqScreenEnter 1s ease forwards;\n}\n\n@keyframes olsMcqScreenEnter{\n  from{\n    opacity:0;\n    transform:translateY(24px) scale(0.96);\n  }\n  to{\n    opacity:1;\n    transform:translateY(0) scale(1);\n  }\n}\n\n.mcq-question-area{\n  background:#eaf0ff;\n  padding:28px 30px 30px;\n  position:relative;\n  height:610px;\n}\n\n.mcq-question-lead{\n  margin:0 0 14px;\n  font-size:24px;\n  line-height:1.35;\n  color:#111827;\n}\n\n.mcq-ionic-table{\n  border-collapse:collapse;\n  width:500px;\n  margin-bottom:8px;\n  font-size:21px;\n  color:#111827;\n}\n\n.mcq-ionic-table th,\n.mcq-ionic-table td{\n  border:1.5px solid #c9ced8;\n  padding:12px 18px;\n  text-align:center;\n}\n\n.mcq-ionic-table th{\n  background:#f2f2f2;\n  font-weight:700;\n}\n\n.mcq-ionic-table td{\n  background:#eaf0ff;\n}\n\n.mcq-question-main{\n  margin:6px 0 28px;\n  font-size:24px;\n  line-height:1.35;\n  color:#111827;\n}\n\n.mcq-options-wrap{\n  display:flex;\n  flex-direction:column;\n  gap:17px;\n  max-width:1200px;\n}\n\n.mcq-option-row{\n  display:flex;\n  align-items:center;\n  min-height:34px;\n  position:relative;\n}\n\n.mcq-radio{\n  width:28px;\n  height:28px;\n  border-radius:50%;\n  border:2px solid #6b7280;\n  margin-right:16px;\n  background:transparent;\n  position:relative;\n  flex:0 0 auto;\n}\n\n.mcq-radio::after{\n  content:\"\";\n  position:absolute;\n  inset:5px;\n  border-radius:50%;\n  background:#6b7280;\n  opacity:0;\n  transform:scale(0.4);\n  transition:\n    opacity 0.25s ease,\n    transform 0.25s ease;\n}\n\n.mcq-option-row.selected .mcq-radio::after{\n  opacity:1;\n  transform:scale(1);\n}\n\n.mcq-option-row.selected .mcq-radio{\n  border-color:#4b5563;\n}\n\n.mcq-radio-ripple{\n  position:absolute;\n  left:14px;\n  top:50%;\n  width:28px;\n  height:28px;\n  border-radius:50%;\n  border:2px solid rgba(28,36,75,0.28);\n  transform:translate(-50%,-50%) scale(1);\n  opacity:0;\n  pointer-events:none;\n}\n\n.mcq-option-row.clicking .mcq-radio-ripple{\n  animation:mcqRipple 0.75s ease forwards;\n}\n\n@keyframes mcqRipple{\n  0%{\n    opacity:0.65;\n    transform:translate(-50%,-50%) scale(1);\n  }\n  100%{\n    opacity:0;\n    transform:translate(-50%,-50%) scale(2.5);\n  }\n}\n\n.mcq-option-label{\n  font-size:23px;\n  color:#111827;\n}\n\n.mcq-specific-feedback{\n  display:inline-flex;\n  align-items:center;\n  margin-left:18px;\n  min-height:38px;\n  opacity:0;\n  transform:translateX(-8px);\n}\n\n.mcq-specific-feedback.show{\n  opacity:1;\n  transform:translateX(0);\n  transition:\n    opacity 0.35s ease,\n    transform 0.35s ease;\n}\n\n.mcq-cross-icon{\n  width:26px;\n  height:26px;\n  border-radius:50%;\n  border:2px solid #d83255;\n  color:#d83255;\n\n  display:inline-flex;\n  justify-content:center;\n  align-items:center;\n\n  font-size:18px;\n  font-weight:700;\n\n  margin-right:12px;\n\n  opacity:0;\n  transform:scale(0.4);\n}\n\n.mcq-cross-icon.show{\n  animation:mcqCrossPop 0.35s ease forwards;\n}\n\n@keyframes mcqCrossPop{\n  70%{\n    opacity:1;\n    transform:scale(1.18);\n  }\n  100%{\n    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line-height:1.34;\n\n  opacity:0;\n  transform:translateY(20px);\n\n  transition:\n    opacity 0.7s ease,\n    transform 0.7s ease;\n\n  overflow:hidden;\n}\n\n.mcq-general-feedback.show{\n  opacity:1;\n  transform:translateY(0);\n}\n\n#mcqGeneralText{\n  white-space:pre-wrap;\n}\n\n.mcq-specific-cursor{\n  background:#111827;\n}\n\n.mcq-general-cursor{\n  background:#8a6a00;\n}\n\n\/* ============================================================\n   3. SHORT ANSWER FEEDBACK\n============================================================ *\/\n\n.ols-saq-stage{\n  width:100vw;\n  height:100vh;\n\n  display:flex;\n  justify-content:center;\n  align-items:center;\n\n  padding:0;\n  overflow:hidden;\n\n  background:\n    radial-gradient(circle at top left,rgba(70,127,247,0.16),transparent 34%),\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\n}\n\n.ols-saq-intro{\n  position:absolute;\n  inset:0;\n  z-index:50;\n\n  display:flex;\n  justify-content:center;\n  align-items:center;\n\n  background:\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\n\n  opacity:1;\n  visibility:visible;\n  pointer-events:none;\n}\n\n.ols-saq-intro.hide{\n  animation:olsSaqIntroFadeOut 0.85s ease forwards;\n}\n\n@keyframes olsSaqIntroFadeOut{\n  to{\n    opacity:0;\n    visibility:hidden;\n  }\n}\n\n.ols-saq-intro-title-wrap{\n  max-width:1250px;\n  padding:0 34px;\n  text-align:center;\n}\n\n.ols-saq-intro-title{\n  margin:0;\n\n  font-family:Poppins,Arial,sans-serif;\n\n  font-size:clamp(52px,8vw,124px);\n  font-weight:600;\n  line-height:1.08;\n\n  color:#1C244B;\n\n  text-shadow:-9px 0 9px rgba(28,36,75,0.16);\n\n  letter-spacing:-0.045em;\n}\n\n#saqIntroTitleText{\n  white-space:pre-wrap;\n}\n\n.ols-saq-scale-wrap{\n  width:calc(var(--ols-saq-screen-w) * 1px);\n  height:calc(var(--ols-saq-screen-h) * 1px);\n\n  transform:scale(var(--ols-saq-screen-scale));\n  transform-origin:center center;\n\n  display:flex;\n  justify-content:center;\n  align-items:flex-start;\n}\n\n.ols-saq-screen{\n  width:1360px;\n  height:965px;\n\n  border-radius:22px;\n  overflow:hidden;\n\n  background:#eaf0ff;\n\n  box-shadow:\n    0 26px 70px rgba(28,36,75,0.22);\n\n  opacity:0;\n  transform:translateY(24px) scale(0.96);\n}\n\n.ols-saq-screen.show{\n  animation:olsSaqScreenEnter 1s ease forwards;\n}\n\n@keyframes olsSaqScreenEnter{\n  from{\n    opacity:0;\n    transform:translateY(24px) scale(0.96);\n  }\n  to{\n    opacity:1;\n    transform:translateY(0) scale(1);\n  }\n}\n\n.saq-question-area{\n  height:335px;\n  background:#eaf0ff;\n  padding:30px 40px 32px;\n}\n\n.saq-question-text{\n  font-size:25px;\n  line-height:1.42;\n  color:#111827;\n  margin-bottom:22px;\n}\n\n.saq-student-box{\n  height:195px;\n\n  background:#f3f4f6;\n\n  border:2px solid #cfd6e3;\n  border-radius:8px;\n\n  padding:23px 26px;\n\n  font-size:24px;\n  line-height:1.55;\n\n  color:#4b5563;\n\n  position:relative;\n  overflow:hidden;\n}\n\n.saq-teacher-feedback{\n  height:630px;\n\n  background:#dff3e6;\n  color:#075f3b;\n\n  padding:28px 40px 30px;\n\n  font-size:23px;\n  line-height:1.47;\n\n  opacity:0;\n  transform:translateY(20px);\n\n  transition:\n    opacity 0.7s ease,\n    transform 0.7s ease;\n\n  overflow:hidden;\n}\n\n.saq-teacher-feedback.show{\n  opacity:1;\n  transform:translateY(0);\n}\n\n#saqTeacherText{\n  white-space:pre-wrap;\n}\n\n.saq-teacher-cursor{\n  background:#075f3b;\n}\n\n\/* ============================================================\n   SMALL WINDOW PROTECTION\n============================================================ *\/\n\n@media(max-width:900px){\n\n  .ols-video-title,\n  .ols-mcq-intro-title,\n  .ols-saq-intro-title{\n    font-size:clamp(42px,11vw,78px);\n    line-height:1.12;\n  }\n\n  .ols-title-cursor{\n    width:4px;\n    margin-left:6px;\n  }\n\n  .ols-video-card{\n    border-radius:20px;\n  }\n\n}\n<\/style>\n<\/head>\n\n<body>\n\n<div class=\"ols-combined-stage\">\n\n  <!-- ========================================================\n       SCENE 1: VIRTUAL LESSON\n  ========================================================= -->\n\n  <section id=\"sceneVideo\" class=\"ols-scene active\">\n\n    <div class=\"ols-video-stage\">\n\n      <div id=\"videoTitleScreen\" class=\"ols-video-title-screen\">\n\n        <div class=\"ols-video-title-wrap\">\n          <h1 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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\n        <main id=\"mcqScreen\" class=\"ols-mcq-screen\">\n\n          <section class=\"mcq-question-area\">\n\n            <p class=\"mcq-question-lead\">Some ionic radii are shown.<\/p>\n\n            <table class=\"mcq-ionic-table\">\n              <thead>\n                <tr>\n                  <th>Ion<\/th>\n                  <th>Ionic radius \/ nm<\/th>\n                <\/tr>\n              <\/thead>\n\n              <tbody>\n                <tr>\n                  <td>Na<sup>+<\/sup><\/td>\n                  <td>0.102<\/td>\n                <\/tr>\n\n                <tr>\n                  <td>K<sup>+<\/sup><\/td>\n                  <td>0.138<\/td>\n                <\/tr>\n\n                <tr>\n                  <td>F<sup>\u2212<\/sup><\/td>\n                  <td>0.133<\/td>\n                <\/tr>\n\n                <tr>\n                  <td>Cl<sup>\u2212<\/sup><\/td>\n                  <td>0.180<\/td>\n                <\/tr>\n              <\/tbody>\n            <\/table>\n\n            <p class=\"mcq-question-main\">Which compound has the strongest ionic bonding?<\/p>\n\n            <div class=\"mcq-options-wrap\">\n\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\">sodium chloride<\/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\">\n                <span class=\"mcq-radio\"><\/span>\n                <span class=\"mcq-radio-ripple\"><\/span>\n                <span class=\"mcq-option-label\">potassium chloride<\/span>\n              <\/div>\n\n              <div class=\"mcq-option-row\">\n                <span class=\"mcq-radio\"><\/span>\n                <span class=\"mcq-radio-ripple\"><\/span>\n                <span class=\"mcq-option-label\">sodium fluoride<\/span>\n              <\/div>\n\n              <div class=\"mcq-option-row\">\n                <span class=\"mcq-radio\"><\/span>\n                <span class=\"mcq-radio-ripple\"><\/span>\n                <span class=\"mcq-option-label\">potassium fluoride<\/span>\n              <\/div>\n\n            <\/div>\n\n            <button id=\"mcqSubmitButton\" class=\"mcq-submit-button\">Submit answer<\/button>\n\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\n        <\/main>\n\n      <\/div>\n\n    <\/div>\n\n  <\/section>\n\n  <!-- ========================================================\n       SCENE 3: SHORT ANSWER FEEDBACK\n  ========================================================= -->\n\n  <section id=\"sceneSaq\" class=\"ols-scene\">\n\n    <div class=\"ols-saq-stage\">\n\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\n        <main id=\"saqScreen\" class=\"ols-saq-screen\">\n\n          <section class=\"saq-question-area\">\n\n            <div class=\"saq-question-text\">\n              <strong>(ii)<\/strong>&nbsp;&nbsp; Melting temperature depends on the strength of metallic bonding.<br>\n              Explain why the metallic bonding in magnesium is much stronger than that in sodium.\n            <\/div>\n\n            <div class=\"saq-student-box\">\n              <span id=\"saqStudentText\"><\/span><span id=\"saqStudentCursor\" class=\"cursor\"><\/span>\n            <\/div>\n\n          <\/section>\n\n          <section id=\"saqTeacherFeedback\" class=\"saq-teacher-feedback\">\n            <span id=\"saqTeacherText\"><\/span><span id=\"saqTeacherCursor\" class=\"cursor saq-teacher-cursor\" 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MULTIPLE CHOICE FEEDBACK\n============================================================ *\/\n\nconst mcqIntroTitle =\n\"Multiple Choice Question Bank\";\n\nconst mcqSpecificFeedbackText =\n\"Na\u207a is small, but Cl\u207b is larger than F\u207b, so the ionic bonding is weaker than in NaF.\";\n\nconst mcqGeneralFeedbackText =\n\"Your answer is incorrect.\\n\\n\" +\n\"To determine which compound has the strongest ionic bonding, recall the key principle:\\n\\n\" +\n\"\u2022 Ionic bond strength increases when ionic radii are small, because the ions can get closer together.\\n\" +\n\"\u2022 Smaller ions \u2192 stronger electrostatic attraction \u2192 stronger ionic lattice.\\n\" +\n\"\u2022 Na\u207a (0.102 nm) is smaller than K\u207a (0.138 nm).\\n\" +\n\"\u2022 F\u207b (0.133 nm) is smaller than Cl\u207b (0.180 nm).\\n\\n\" +\n\"Therefore, the strongest ionic bonding occurs in the compound formed by the smallest cation and the smallest anion \u2192 sodium fluoride (NaF).\\n\\n\" +\n\"The correct answer is: sodium fluoride\";\n\nconst mcqIntroScreen =\ndocument.getElementById(\"mcqIntroScreen\");\n\nconst mcqIntroTitleText =\ndocument.getElementById(\"mcqIntroTitleText\");\n\nconst mcqIntroTitleCursor =\ndocument.getElementById(\"mcqIntroTitleCursor\");\n\nconst mcqScreen =\ndocument.getElementById(\"mcqScreen\");\n\nconst mcqWrongOption =\ndocument.getElementById(\"mcqWrongOption\");\n\nconst mcqSubmitButton =\ndocument.getElementById(\"mcqSubmitButton\");\n\nconst mcqSpecificFeedback =\ndocument.getElementById(\"mcqSpecificFeedback\");\n\nconst mcqCrossIcon =\ndocument.getElementById(\"mcqCrossIcon\");\n\nconst mcqSpecificText =\ndocument.getElementById(\"mcqSpecificText\");\n\nconst mcqSpecificCursor =\ndocument.getElementById(\"mcqSpecificCursor\");\n\nconst mcqGeneralFeedback =\ndocument.getElementById(\"mcqGeneralFeedback\");\n\nconst mcqGeneralText =\ndocument.getElementById(\"mcqGeneralText\");\n\nconst mcqGeneralCursor =\ndocument.getElementById(\"mcqGeneralCursor\");\n\nfunction selectMcqWrongOption(){\n\n  mcqWrongOption.classList.add(\"clicking\");\n\n  setTimeout(() => {\n    mcqWrongOption.classList.add(\"selected\");\n  },220);\n\n  setTimeout(() => {\n    mcqWrongOption.classList.remove(\"clicking\");\n  },850);\n\n}\n\nfunction clickMcqSubmit(){\n\n  mcqSubmitButton.classList.add(\"clicked\");\n\n  setTimeout(() => {\n    mcqSubmitButton.classList.remove(\"clicked\");\n  },240);\n\n}\n\nfunction showMcqSpecificFeedback(){\n\n  mcqSpecificFeedback.classList.add(\"show\");\n\n  setTimeout(() => {\n    mcqCrossIcon.classList.add(\"show\");\n  },180);\n\n  setTimeout(() => {\n\n    mcqSpecificCursor.style.display = \"inline-block\";\n\n    typeWriter(mcqSpecificText,mcqSpecificFeedbackText,12,() => {\n\n      mcqSpecificCursor.style.display = \"none\";\n\n      setTimeout(() => {\n        showMcqGeneralFeedback();\n      },650);\n\n    });\n\n  },560);\n\n}\n\nfunction showMcqGeneralFeedback(){\n\n  mcqGeneralFeedback.classList.add(\"show\");\n\n  setTimeout(() => {\n\n    mcqGeneralCursor.style.display = \"inline-block\";\n\n    typeWriter(mcqGeneralText,mcqGeneralFeedbackText,8,() => {\n\n      mcqGeneralCursor.style.display = \"none\";\n\n      setTimeout(() => {\n\n        switchScene(sceneMcq,sceneSaq,() => {\n          startSaqIntro();\n        });\n\n      },2600);\n\n    });\n\n  },600);\n\n}\n\nfunction startMcqAnimation(){\n\n  fitMcqScreen();\n\n  mcqScreen.classList.add(\"show\");\n\n  setTimeout(() => {\n\n    selectMcqWrongOption();\n\n    setTimeout(() => {\n\n      clickMcqSubmit();\n\n      setTimeout(() => {\n\n        showMcqSpecificFeedback();\n\n      },620);\n\n    },1150);\n\n  },1300);\n\n}\n\nfunction startMcqIntro(){\n\n  fitMcqScreen();\n\n  setTimeout(() => {\n\n    typeWriter(mcqIntroTitleText,mcqIntroTitle,44,() => {\n\n      setTimeout(() => {\n\n        mcqIntroTitleCursor.style.display = \"none\";\n\n        setTimeout(() => {\n\n          mcqIntroScreen.classList.add(\"hide\");\n\n          setTimeout(() => {\n            startMcqAnimation();\n          },850);\n\n        },3000);\n\n      },250);\n\n    });\n\n  },700);\n\n}\n\n\/* ============================================================\n   3. SHORT ANSWER FEEDBACK\n============================================================ *\/\n\nconst saqIntroTitle =\n\"Chemistry Specialist\\nMarked Exam Feedback\";\n\nconst saqStudentAnswer =\n\"Magnesium has stronger metallic bonding because it has more atoms packed together and melts at a higher temperature than sodium.\";\n\nconst saqTeacherFeedbackText =\n\"Comment:\\n\" +\n\"This answer is not correct. Melting temperature is a result of bonding strength, not the cause of it.\\n\\n\" +\n\"In metallic bonding, positive metal ions are attracted to a sea of delocalised electrons. The strength of this attraction depends on the charge of the ions and the number of delocalised electrons.\\n\\n\" +\n\"Magnesium forms Mg\u00b2\u207a ions and contributes two delocalised electrons per atom, whereas sodium forms Na\u207a ions and contributes only one electron. This results in a stronger electrostatic attraction in magnesium. Additionally, Mg\u00b2\u207a ions have a higher charge density than Na\u207a ions, further strengthening the metallic bonding.\\n\\n\" +\n\"Next time, include:\\n\" +\n\"\u2022 Ion charge: magnesium forms Mg\u00b2\u207a, sodium forms Na\u207a \u2713\\n\" +\n\"\u2022 Delocalised electrons: magnesium provides more electrons to the sea \u2713\\n\" +\n\"\u2022 Charge density: smaller, more highly charged ions create stronger attraction \u2713\\n\\n\" +\n\"You were close. 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It is also called Z.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What is the mass number?<\/h3>\n            <p>The mass number is the total number of protons and neutrons in the nucleus of an atom. It is also called A.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>How do you calculate the number of neutrons?<\/h3>\n            <p>Use number of neutrons = mass number &#8211; atomic number. In symbols, this is A &#8211; Z.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What are isotopes?<\/h3>\n            <p>Isotopes are atoms with the same number of protons but different numbers of neutrons.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why do isotopes have similar chemical properties?<\/h3>\n            <p>Isotopes of the same element have the same number of electrons and the same electronic structure, so they normally react in similar ways.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-related-card\">\n        <h2>Related Atomic Structure Revision Notes<\/h2>\n        <p>Continue through Topic 1 by linking atomic structure to mass spectrometry, electron configuration 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\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/\">Mass Spectrometry<\/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\/electron-configuration\/\">Electron Configuration<\/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\/ionisation-energy\/\">Ionisation Energy<\/a>\n        <\/div>\n      <\/section>\n\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: 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: 760px) {\n            .ols-attribution-card {\n              padding: 24px 18px;\n              border-radius: 22px;\n            }\n          }\n        <\/style>\n      \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. 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