{"id":4517,"date":"2026-05-28T06:03:53","date_gmt":"2026-05-28T05:03:53","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/periodic-trends\/"},"modified":"2026-05-29T07:23:07","modified_gmt":"2026-05-29T06:23:07","slug":"periodic-trends","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/periodic-trends\/","title":{"rendered":"Periodic Trends"},"content":{"rendered":"\n<!--\n===============================================================================\nONLINE LEARNING SYSTEM COPYRIGHT NOTICE\n\u00a9 Online Learning System. 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display: block; margin-bottom: 6px; font-size: 13px; font-weight: 700; color: var(--blue); }\n    }\n  <\/style>\n\n  <div class=\"ols-revision-layout\">\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>Periodic Trends<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Periodic Trends<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to periodicity: atomic radius and ionisation energy trends across a period and down a group, melting and boiling point trends across Period 3, and how physical properties link to bonding and structure for Edexcel A Level Chemistry (9CH0).<\/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          <img decoding=\"async\" class=\"ols-author-avatar-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\" alt=\"Dr. Mohammed Al-Fatah\">\n          <div class=\"ols-author-content\">\n            <h2 class=\"ols-author-title\">Written by:<br><span>Dr. Mohammed Al-Fatah<\/span><\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/p>\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\"><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\"><\/path><\/svg>\n              View LinkedIn Profile\n            <\/a>\n          <\/div>\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 Is Periodicity?<\/h2><\/div>\n        <p><strong>Periodicity<\/strong> refers to the repeating pattern of chemical and physical properties seen across different periods of the periodic table. The same pattern appears in Period 2 and Period 3 because electrons are added to the same types of subshells in the same sequence.<\/p>\n        <p>The 9CH0 specification requires you to understand periodicity in terms of a repeating pattern, and to explain trends in melting and boiling temperatures, ionisation energy and atomic radius across periods 2 and 3.<\/p>\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> periodic trends repeat because the electronic structure of each period follows the same pattern of subshell filling.<\/p>\n        <\/div>\n      <\/article>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">2<\/div><h2>Atomic Radius Across a Period<\/h2><\/div>\n        <p>Atomic radius generally <strong>decreases across a period<\/strong>. As proton number increases, nuclear charge increases. Electrons are added to the same main shell, so shielding remains similar. The stronger nuclear attraction pulls the electron cloud closer to the nucleus.<\/p>\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\">\n            <h3>Nuclear charge increases<\/h3>\n            <p>More protons in the nucleus attract the outer electrons more strongly, pulling them closer.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Shielding stays similar<\/h3>\n            <p>Electrons enter the same main shell, so no significant extra inner-shell shielding is added.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Atomic radius decreases<\/h3>\n            <p>The stronger attraction reduces the distance between the nucleus and the outer electrons.<\/p>\n          <\/div>\n        <\/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\/Atomic-radius-trend-across-Period-3.webp\" alt=\"Atomic radius trend across Period 3\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>Across a period, atomic radius decreases because nuclear charge increases while shielding remains similar.<\/p>\n        <\/div>\n      <\/div>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">3<\/div><h2>Ionisation Energy Compared Across a Period and Down a Group<\/h2><\/div>\n        <p>It is useful to separate the two directions clearly. <strong>Across a period<\/strong>, electrons are added to the same main shell, so shielding remains similar and atomic radius decreases. First ionisation energy generally increases.<\/p>\n        <p><strong>Down a group<\/strong>, electrons are added to new shells. This gives a larger atomic radius and more shielding, so first ionisation energy decreases.<\/p>\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Direction<\/th>\n                <th>Atomic radius<\/th>\n                <th>Shielding<\/th>\n                <th>First ionisation energy<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Direction\">Across a period (left to right)<\/td>\n                <td data-label=\"Atomic radius\">Decreases<\/td>\n                <td data-label=\"Shielding\">Similar<\/td>\n                <td data-label=\"First ionisation energy\">Generally increases<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Direction\">Down a group<\/td>\n                <td data-label=\"Atomic radius\">Increases<\/td>\n                <td data-label=\"Shielding\">Increases<\/td>\n                <td data-label=\"First ionisation energy\">Decreases<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/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>Melting and Boiling Point Trends Across Period 3<\/h2><\/div>\n        <p>Across Period 3, melting and boiling points do <strong>not<\/strong> follow the same pattern as ionisation energy. This is because melting and boiling points depend on <strong>bonding and structure<\/strong>, not on how tightly electrons are held.<\/p>\n        <p>Sodium, magnesium and aluminium are metallic solids with giant metallic structures. Silicon has a giant covalent structure with very strong bonds throughout. Phosphorus, sulfur, chlorine and argon are simple molecular or monatomic, so their melting and boiling points are low and depend on weak intermolecular forces.<\/p>\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> do not explain melting point trends using ionisation energy arguments. Melting point depends on the type of bonding and structure, not on the energy needed to remove an electron.<\/p>\n        <\/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\/Melting-and-boiling-points-across-Period-3.webp\" alt=\"Melting and boiling points across Period 3\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>Physical property trends depend on bonding and structure, so they should not be explained using ionisation energy arguments alone.<\/p>\n        <\/div>\n      <\/div>\n\n      <article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">5<\/div><h2>Using Data to Illustrate Periodicity<\/h2><\/div>\n        <p>The 9CH0 specification asks you to illustrate periodicity using data, including electronic configurations, atomic radii, melting and boiling temperatures and first ionisation energies (spec point 26).<\/p>\n        <p>When answering these questions, state the trend clearly, identify the direction (across a period or down a group) and explain the cause using nuclear charge, shielding, atomic radius and the type of bonding or structure.<\/p>\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\">\n            <h3>Electronic configuration<\/h3>\n            <p>Repeating pattern of subshell filling from s to p explains why properties repeat across periods.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Atomic radius<\/h3>\n            <p>Decreases across a period (nuclear charge dominates), increases down a group (extra shells).<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>Melting and boiling temperatures<\/h3>\n            <p>Determined by structure: metallic, giant covalent, or simple molecular\/monatomic.<\/p>\n          <\/div>\n          <div class=\"ols-rule-item\">\n            <h3>First ionisation energies<\/h3>\n            <p>Generally increase across a period; decrease down a group. 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.ols-course-button {\n              width: 100%;\n            }\n          }\n        <\/style>\n      \n        <div class=\"ols-course-cta-card\">\n      \n          <div class=\"ols-course-cta-top\">\n      \n            <a class=\"ols-course-cta-image-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/atomic-structure-and-the-periodic-table-topic-1\/\" aria-label=\"Open the Edexcel A Level Chemistry Topic 1 Atomic Structure and The Periodic Table course 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              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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  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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  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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  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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 class=\"ols-video-title\">\n            <span id=\"videoTitleText\"><\/span><span id=\"videoTitleCursor\" class=\"ols-title-cursor\"><\/span>\n          <\/h1>\n        <\/div>\n\n      <\/div>\n\n      <section id=\"videoScene\" class=\"ols-video-scene\">\n\n        <div class=\"ols-video-scale-wrap\">\n\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\n        <\/div>\n\n      <\/section>\n\n    <\/div>\n\n  <\/section>\n\n  <!-- ========================================================\n       SCENE 2: MULTIPLE CHOICE FEEDBACK\n  ========================================================= -->\n\n  <section id=\"sceneMcq\" class=\"ols-scene\">\n\n    <div class=\"ols-mcq-stage\">\n\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\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\" style=\"display:none;\"><\/span>\n          <\/section>\n\n        <\/main>\n\n      <\/div>\n\n    <\/div>\n\n  <\/section>\n\n<\/div>\n\n<script>\n\/* ============================================================\n   70% VIEWPORT PLAY \/ PAUSE CONTROLLER\n============================================================ *\/\n\nconst olsStage =\ndocument.querySelector(\".ols-combined-stage\");\n\nlet olsAnimationHasStarted = false;\nlet olsAnimationIsVisibleEnough = false;\nlet olsAnimationPaused = true;\n\nconst olsNativeSetTimeout = window.setTimeout.bind(window);\nconst olsNativeClearTimeout = window.clearTimeout.bind(window);\nconst olsPausableTimers = new Map();\nlet olsPausableTimerId = 1;\n\nwindow.setTimeout = function(callback,delay,...args){\n\n  const timerId = olsPausableTimerId++;\n\n  const timer = {\n    callback,\n    delay:Number(delay) || 0,\n    remaining:Number(delay) || 0,\n    args,\n    startedAt:Date.now(),\n    nativeId:null,\n    completed:false\n  };\n\n  function 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*\/\n\ninitialiseOlsVisibilityControlledAnimation();\n<\/script>\n\n<\/body>\n<\/html>\n        <\/template>\n      \n        <script>\n          (function(){\n            var startButton = document.getElementById(\"olsCourseAnimationStart002\");\n            var pauseButton = document.getElementById(\"olsCourseAnimationPause002\");\n            var iframe = document.getElementById(\"olsCourseAnimationFrame002\");\n            var template = document.getElementById(\"olsCourseAnimationTemplate002\");\n      \n            if (!startButton || !pauseButton || !iframe || !template) {\n              return;\n            }\n      \n            var olsAnimationPausedFromButton = false;\n      \n            startButton.addEventListener(\"click\", function(){\n              iframe.setAttribute(\"srcdoc\", template.innerHTML);\n              startButton.classList.add(\"is-hidden\");\n              pauseButton.classList.add(\"is-visible\");\n              pauseButton.textContent = \"Pause\";\n    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             pauseButton.textContent = \"Pause\";\n                pauseButton.setAttribute(\"aria-label\", \"Pause course preview animation\");\n              }\n            });\n          })();\n        <\/script>\n      <\/section>\n\n      <section class=\"ols-faq-card\">\n        <h2>FAQs: Periodic Trends<\/h2>\n        <p>Use these questions to secure the key reasoning for periodic trend exam answers.<\/p>\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>What is periodicity?<\/h3>\n            <p>Periodicity is the repeating pattern of physical and chemical properties seen across different periods of the periodic table, caused by the repeated pattern of subshell filling.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why does atomic radius decrease across a period?<\/h3>\n            <p>Nuclear charge increases while electrons are added to the same main shell, so shielding remains similar and the stronger nuclear attraction pulls the electron cloud closer to the nucleus.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why do melting and boiling points not follow the same trend as ionisation energy across a period?<\/h3>\n            <p>Melting and boiling points depend on bonding and structure. Metallic elements have giant metallic structures, silicon has a giant covalent structure, and the other Period 3 elements are simple molecular or monatomic with weak intermolecular forces.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why does first ionisation energy generally increase across a period?<\/h3>\n            <p>As proton number increases, nuclear charge increases but shielding remains similar because electrons enter the same main shell. The stronger attraction between the nucleus and the outer electron means more energy is needed to remove it.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why does first ionisation energy decrease down a group?<\/h3>\n            <p>Going down a group, atoms have more occupied electron shells. The outer electron is further from the nucleus and shielded more strongly by inner shells, so less energy is needed to remove it.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Continue through Topic 1 by linking periodic trends to ionisation energy, electron configuration and bonding.<\/p>\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\/ionisation-energy\/\">Ionisation Energy<\/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\/trends-in-a-period\/\">Trends in a Period<\/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\/trends-in-a-group\/\">Trends in a Group<\/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\/atomic-structure\/\">Atomic Structure<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/\">Bonding &amp; Structure<\/a>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-attribution-card\">\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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