{"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":"2026-10-25T12:15:23","modified_gmt":"2026-10-25T12:15:23","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. All rights reserved.\n\nBackend copyright marker: OLS-T1-PERIODIC-TRENDS-REVISION-PAGE-9CH0-2026\n\nPage: Periodic Trends\nEdexcel A Level Chemistry (9CH0)\nPaper 1: Advanced Inorganic and Physical Chemistry\nTopic 1: Atomic Structure & The Periodic Table\n9CH0\/01\n===============================================================================\n-->\n\n<section class=\"ols-revision-page ols-periodic-trends-9ch0-page\" data-owner=\"Online Learning System\" data-copyright=\"\u00a9 Online Learning System. All rights reserved.\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --soft-orange: #fff7ed;\n      --gold: #c9973a;\n      --grey-text: #667085;\n      --body-text: #1f2937;\n      --border: rgba(28, 36, 75, 0.14);\n      --shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      --inner-shadow: 0 10px 26px rgba(28, 36, 75, 0.08);\n      font-family: Poppins, Arial, sans-serif;\n      color: var(--navy);\n      background: #ffffff;\n    }\n    .ols-revision-page * { box-sizing: border-box; }\n    .ols-revision-layout { display: grid; grid-template-columns: 310px minmax(0, 1fr); gap: 34px; max-width: 1450px; margin: 0 auto; padding: 24px 20px 60px; }\n    .ols-main { min-width: 0; max-width: 970px; }\n    .ols-breadcrumbs { display: flex; flex-wrap: wrap; gap: 8px; margin: 10px 0 22px; font-size: 15px; color: var(--grey-text); }\n    .ols-breadcrumbs a, .ols-breadcrumbs span { color: var(--grey-text); text-decoration: none; font-weight: 600; }\n    .ols-breadcrumbs a:hover { color: var(--blue); text-decoration: underline; text-underline-offset: 3px; }\n    .ols-title-card, .ols-note-card, .ols-h5p-card, .ols-related-card, .ols-faq-card, .ols-quicksnap-card { background: #ffffff; border: 1px solid var(--border); border-radius: 28px; box-shadow: var(--shadow); padding: 34px; margin-bottom: 24px; overflow: hidden; }\n    .ols-title-card { background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%); }\n    .ols-title-card h1 { margin: 0 0 18px; font-size: clamp(36px, 5vw, 58px); line-height: 1.08; font-weight: 800; letter-spacing: -0.04em; color: #111827; }\n    .ols-page-intro { font-size: 19px; line-height: 1.7; font-weight: 300; color: var(--body-text); margin: 0 0 22px; }\n    .ols-badges { display: flex; flex-direction: column; align-items: flex-start; gap: 12px; margin-bottom: 22px; }\n    .ols-badge { display: inline-flex; align-items: center; padding: 9px 14px; border-radius: 999px; background: #ffffff; border: 1px solid var(--border); font-size: 15px; font-weight: 600; color: var(--navy); }\n    .ols-author { display: flex; align-items: center; gap: 20px; padding: 28px; border-radius: 28px; background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%); border: 1px solid rgba(28,36,75,0.12); box-shadow: 0 18px 45px rgba(28,36,75,0.10); margin-top: 22px; }\n    .ols-author-avatar-img { width: 92px; height: 92px; border-radius: 50%; object-fit: cover; object-position: center; flex-shrink: 0; border: 4px solid #ffffff; box-shadow: 0 14px 32px rgba(28,36,75,0.18), 0 0 0 1px rgba(28,36,75,0.10); transition: transform 0.25s ease, box-shadow 0.25s ease; }\n    .ols-author:hover .ols-author-avatar-img { transform: scale(1.04); box-shadow: 0 20px 42px rgba(28,36,75,0.22), 0 0 0 1px rgba(28,36,75,0.10); }\n    .ols-author-content { min-width: 0; }\n    .ols-author-title { margin: 0 0 4px; font-size: clamp(24px,3vw,34px); line-height: 1.15; font-weight: 700; color: var(--navy); letter-spacing: -0.03em; }\n    .ols-author-description { margin: 0; font-size: 17px; line-height: 1.7; font-weight: 300; color: var(--grey-text); }\n    .ols-linkedin-pill { display: inline-flex; align-items: center; justify-content: center; gap: 10px; margin-top: 16px; padding: 11px 18px; border-radius: 999px; background: linear-gradient(135deg,#0A66C2,#004182); color: #ffffff; text-decoration: none; font-size: 14px; line-height: 1; font-weight: 700; letter-spacing: 0.01em; box-shadow: 0 10px 22px rgba(10,102,194,0.24); position: relative; overflow: hidden; transition: transform 0.22s ease, box-shadow 0.22s ease; }\n    .ols-linkedin-pill::before { content: \"\"; position: absolute; top: 0; left: -120%; width: 100%; height: 100%; background: linear-gradient(120deg, rgba(255,255,255,0) 0%, rgba(255,255,255,0.28) 50%, rgba(255,255,255,0) 100%); transition: left 0.7s ease; }\n    .ols-linkedin-pill:hover { transform: translateY(-3px) scale(1.03); box-shadow: 0 16px 34px rgba(10,102,194,0.34), 0 0 0 6px rgba(10,102,194,0.10); color: #ffffff; }\n    .ols-linkedin-pill:hover::before { left: 120%; }\n    .ols-linkedin-icon { width: 18px; height: 18px; display: block; flex-shrink: 0; }\n    .ols-note-card.soft { background: linear-gradient(135deg, #ffffff 0%, var(--soft-red) 100%); }\n    .ols-note-card.purple { background: linear-gradient(135deg, #ffffff 0%, var(--soft-purple) 100%); }\n    .ols-note-card.orange { background: linear-gradient(135deg, #ffffff 0%, var(--soft-orange) 100%); }\n    .ols-note-title { display: flex; align-items: center; gap: 14px; margin-bottom: 20px; }\n    .ols-note-icon { width: 52px; height: 52px; border-radius: 16px; background: var(--navy); color: #ffffff; display: grid; place-items: center; font-size: 24px; font-weight: 800; flex-shrink: 0; }\n    .ols-note-title h2, .ols-h5p-card h2, .ols-related-card h2, .ols-faq-card h2 { margin: 0; font-size: clamp(28px, 3.5vw, 42px); line-height: 1.15; font-weight: 800; color: #111827; letter-spacing: -0.03em; }\n    .ols-h5p-card h2, .ols-related-card h2, .ols-faq-card h2 { margin-bottom: 14px; }\n    .ols-note-card p, .ols-note-card li { font-size: clamp(15px, 1.25vw, 17px); line-height: 1.65; font-weight: 300; color: var(--body-text); }\n    .ols-h5p-card p, .ols-related-card p, .ols-faq-card p { font-size: clamp(15px, 1.3vw, 18px); line-height: 1.65; font-weight: 300; color: var(--body-text); }\n    .ols-note-card strong, .ols-h5p-card strong, .ols-related-card strong, .ols-faq-card strong { font-weight: 700; color: var(--navy); }\n    .ols-note-card ul, .ols-note-card ol { margin: 0; padding-left: 22px; }\n    .ols-key-box { margin-top: 20px; background: var(--soft-green); border: 1px solid rgba(63, 143, 70, 0.25); border-radius: 20px; padding: 18px 20px; }\n    .ols-key-box p { margin: 0; font-weight: 400; color: var(--navy); }\n    .ols-rule-list { display: grid; gap: 14px; margin-top: 18px; }\n    .ols-rule-item { background: #ffffff; border: 1px solid var(--border); border-left: 5px solid var(--blue); border-radius: 18px; padding: 18px; box-shadow: var(--inner-shadow); }\n    .ols-rule-item h3 { margin: 0 0 8px; font-size: 20px; line-height: 1.25; color: var(--navy); }\n    .ols-rule-item p { margin: 0; font-size: 15px; line-height: 1.6; }\n    .ols-definition-box { background: linear-gradient(135deg, #ffffff, var(--soft-purple)); border: 2px dashed rgba(122, 62, 157, 0.35); border-radius: 24px; padding: 24px; margin-top: 22px; }\n    .ols-definition-box p { margin: 0; }\n    .ols-table-wrap { overflow: hidden; border-radius: 22px; border: 1px solid var(--border); background: #ffffff; margin-top: 18px; }\n    .ols-table { width: 100%; border-collapse: collapse; table-layout: fixed; }\n    .ols-table th { background: var(--navy); color: #ffffff; padding: 16px; text-align: left; font-size: clamp(14px, 1.2vw, 17px); font-weight: 600; overflow-wrap: anywhere; }\n    .ols-table td { padding: 16px; border-bottom: 1px solid var(--border); font-size: clamp(14px, 1.15vw, 16px); line-height: 1.45; color: var(--body-text); vertical-align: top; overflow-wrap: anywhere; }\n    .ols-table tr:last-child td { border-bottom: none; }\n    .ols-faq-list { display: grid; gap: 14px; margin-top: 18px; }\n    .ols-faq-item { background: #ffffff; border: 1px solid var(--border); border-radius: 18px; padding: 18px 20px; box-shadow: var(--inner-shadow); }\n    .ols-faq-item h3 { margin: 0 0 8px; font-size: 20px; line-height: 1.3; color: var(--navy); }\n    .ols-faq-item p { margin: 0; font-size: 16px; line-height: 1.65; color: var(--body-text); }\n    .ols-related-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 16px; margin-top: 18px; }\n    .ols-related-item { border: 1px solid var(--border); border-radius: 18px; padding: 18px; background: #ffffff; color: var(--navy); text-decoration: none; font-weight: 600; line-height: 1.5; transition: transform 0.2s ease, box-shadow 0.2s ease; }\n    .ols-related-item:hover { transform: translateY(-2px); box-shadow: 0 10px 22px rgba(28, 36, 75, 0.08); color: var(--blue); }\n    .ols-attribution-card { background: linear-gradient(135deg, #ffffff, #f8fbff); border: 1px solid rgba(28, 36, 75, 0.14); border-radius: 28px; box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10); padding: 34px; margin-bottom: 24px; overflow: hidden; font-family: Poppins, Arial, sans-serif; box-sizing: border-box; }\n    .ols-attribution-card p { margin: 0; font-size: 14px; line-height: 1.65; font-weight: 300; color: #667085; }\n    .ols-attribution-card strong { font-weight: 700; color: #1C244B; }\n\n    .ols-zoom-card, .ols-zoom-card * { box-sizing: border-box; }\n    .ols-zoom-card { display: block !important; margin: 26px 0 34px !important; border: 1px solid rgba(28, 36, 75, 0.14) !important; border-radius: 26px !important; background: #ffffff !important; box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10) !important; overflow: visible !important; position: relative !important; z-index: 1 !important; isolation: isolate !important; }\n    .ols-zoom-card:hover { z-index: 50 !important; }\n    .ols-zoom-card-image { display: flex !important; align-items: center !important; justify-content: center !important; width: 100% !important; min-height: 330px !important; padding: 20px !important; background: #ffffff !important; overflow: visible !important; border-top-left-radius: 26px !important; border-top-right-radius: 26px !important; position: relative !important; z-index: 2 !important; }\n    .ols-zoom-card img.ols-zoomable-img { display: block !important; width: 100% !important; max-width: 100% !important; height: auto !important; border-radius: 18px !important; cursor: default !important; pointer-events: auto !important; user-select: none !important; -webkit-user-drag: none !important; transform: translateZ(0) scale(1) !important; transform-origin: center center !important; transition: transform 0.32s ease, box-shadow 0.32s ease, filter 0.32s ease !important; position: relative !important; z-index: 2 !important; }\n    @media (hover: hover) and (pointer: fine) { .ols-zoom-card img.ols-zoomable-img:hover { transform: translateZ(0) scale(1.45) !important; box-shadow: 0 28px 70px rgba(28, 36, 75, 0.34) !important; filter: saturate(1.02) contrast(1.01) !important; z-index: 100 !important; } }\n    .ols-zoom-card-caption { padding: 18px 22px 20px !important; background: linear-gradient(135deg, #ffffff, #f8fbff) !important; border-bottom-left-radius: 26px !important; border-bottom-right-radius: 26px !important; position: relative !important; z-index: 1 !important; }\n    .ols-zoom-card-caption p { margin: 0 !important; color: #5f6b85 !important; font-size: 15px !important; line-height: 1.65 !important; font-weight: 300 !important; font-style: italic !important; font-family: Poppins, Arial, sans-serif !important; }\n    .ols-zoom-card img.ols-lightbox-target { cursor: zoom-in !important; }\n    @media (max-width: 760px) { .ols-zoom-card { border-radius: 22px !important; overflow: hidden !important; } .ols-zoom-card-image { min-height: auto !important; padding: 12px !important; overflow: hidden !important; } .ols-zoom-card img.ols-zoomable-img, .ols-zoom-card img.ols-zoomable-img:hover { transform: none !important; box-shadow: none !important; } }\n    .ols-image-lightbox { position: fixed; inset: 0; z-index: 999999; display: none; align-items: center; justify-content: center; padding: 34px; background: rgba(10, 15, 35, 0.86); backdrop-filter: blur(8px); -webkit-backdrop-filter: blur(8px); }\n    .ols-image-lightbox.is-open { display: flex; }\n    .ols-image-lightbox-inner { position: relative; width: min(96vw, 1500px); max-height: 92vh; display: flex; align-items: center; justify-content: center; }\n    .ols-image-lightbox-img { display: block; max-width: 100%; max-height: 92vh; height: auto; width: auto; border-radius: 22px; background: #ffffff; box-shadow: 0 32px 90px rgba(0,0,0,0.45); object-fit: contain; }\n    .ols-image-lightbox-close { position: absolute; top: -18px; right: -18px; width: 46px; height: 46px; border: 0; border-radius: 50%; background: #ffffff; color: #1C244B; font-family: Poppins, Arial, sans-serif; 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: #2563eb; color: #ffffff; }\n\n    @media (max-width: 1050px) {\n      .ols-revision-layout { grid-template-columns: 1fr; }\n      .ols-main { max-width: none; }\n      .ols-related-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }\n    }\n    @media (max-width: 760px) {\n      .ols-revision-layout { padding: 14px 12px 44px; }\n      .ols-title-card, .ols-note-card, .ols-h5p-card, .ols-related-card, .ols-faq-card, .ols-attribution-card { padding: 24px 18px; border-radius: 22px; }\n      .ols-note-title { align-items: flex-start; }\n      .ols-related-grid { grid-template-columns: 1fr; }\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-image-lightbox { padding: 16px; }\n      .ols-image-lightbox-inner { width: 100%; max-height: 88vh; }\n      .ols-image-lightbox-img { max-height: 88vh; border-radius: 16px; }\n      .ols-image-lightbox-close { top: 10px; right: 10px; width: 42px; height: 42px; font-size: 26px; }\n      .ols-table-wrap { border: none; background: transparent; }\n      .ols-table, .ols-table thead, .ols-table tbody, .ols-table th, .ols-table td, .ols-table tr { display: block; width: 100%; }\n      .ols-table { border-collapse: separate; border-spacing: 0; }\n      .ols-table thead { display: none; }\n      .ols-table tr { margin-bottom: 14px; border: 1px solid var(--border); border-radius: 18px; overflow: hidden; background: #ffffff; box-shadow: var(--inner-shadow); }\n      .ols-table td { border-bottom: 1px solid var(--border); padding: 14px 16px; overflow-wrap: anywhere; }\n      .ols-table td:last-child { border-bottom: none; }\n      .ols-table td::before { content: attr(data-label); 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 temperature 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      <\/header>\n\n      <section class=\"ols-h5p-card ols-h5p-inline ols-h5p-recap\">\n<span class=\"ols-h5p-kicker\">Before you start<\/span>\n<h2>GCSE Recap: Groups, Periods and Outer Electrons<\/h2>\n<p>Three quick GCSE questions on the layout of the periodic table before you meet the trends that layout produces.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"788\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">1<\/div><h2>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 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<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Atomic Radius in Period 4<\/h2>\n<p>Take the reasoning of this card into a period the page has not used.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-475\" class=\"h5p-iframe\" data-content-id=\"475\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Periodic Trends MCQ: Two Atoms From Period 4\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <div class=\"ols-zoom-card\">\n        <div class=\"ols-zoom-card-image\">\n          <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/wave-37.jpg\" alt=\"Line graph of covalent radius across Period 3, Na to Cl, with argon marked as having no comparable radius, a why panel and a key-idea strip\" 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<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Going Down a Group<\/h2>\n<p>Build the explanation for the direction the page gives no data for.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-473\" class=\"h5p-iframe\" data-content-id=\"473\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Periodic Trends Drag: Down the Group 2 Metals\"><\/iframe><\/div><\/div>\n<\/section>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Five Pairs of Elements<\/h2>\n<p>Decide each pair quickly, using both directions of the table.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-476\" class=\"h5p-iframe\" data-content-id=\"476\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Periodic Trends Rapid Check: Five Pairs of Elements\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">4<\/div><h2>Melting and Boiling Temperature Trends Across Period 3<\/h2><\/div>\n        <p>Across Period 3, melting and boiling temperatures do <strong>not<\/strong> follow the same pattern as ionisation energy. This is because melting and boiling temperatures 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.<\/p>\n<p>Silicon has a giant covalent structure with very strong bonds throughout.<\/p>\n<p>Phosphorus, sulfur, chlorine and argon are simple molecular or monatomic, so their melting and boiling temperatures 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 temperature trends using ionisation energy arguments. Melting temperature depends on the type of bonding and structure, not on the energy needed to remove an electron.<\/p>\n        <\/div>\n      <\/article>\n<!-- 3D card: period3-structures-mp (5 Oct 2026, Topics 1-5 upgrade) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. All rights reserved. -->\n<section class=\"ols-ptsm-001\" id=\"olsPtsm001\">\n<style>\n@import url('https:\/\/fonts.googleapis.com\/css2?family=Poppins:wght@300;400;500;600&display=swap');\n\n.ols-ptsm-001{\n  font-family:'Poppins',system-ui,-apple-system,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;\n  color:#1C244B; background:#ffffff;\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:44px; margin:26px auto; max-width:980px;\n  box-sizing:border-box; -webkit-font-smoothing:antialiased;\n}\n.ols-ptsm-001 *{box-sizing:border-box;}\n\n.ols-ptsm-001 .ptsm-head{margin:0 0 22px;}\n.ols-ptsm-001 h2.ptsm-title{\n  font-size:26px; line-height:1.25; font-weight:600; letter-spacing:-0.012em;\n  margin:0 0 9px; color:#1C244B;\n}\n.ols-ptsm-001 p.ptsm-sub{\n  font-size:14.5px; line-height:1.62; font-weight:300; color:#4a5270;\n  margin:0; max-width:66ch;\n}\n\n.ols-ptsm-001 .ptsm-stage{\n  position:relative; width:100%; height:550px;\n  background:#ffffff; border:1px solid rgba(28,36,75,0.12);\n  border-radius:18px; overflow:hidden;\n}\n.ols-ptsm-001 .ptsm-canvas{\n  display:block; width:100%; height:100%;\n  touch-action:none; cursor:grab; background:#ffffff;\n}\n.ols-ptsm-001 .ptsm-canvas.is-drag{cursor:grabbing;}\n.ols-ptsm-001 .ptsm-overlay{position:absolute; inset:0; pointer-events:none; overflow:hidden;}\n\n.ols-ptsm-001 .ptsm-lab{\n  position:absolute; left:0; top:0; transform:translate(-50%,-50%);\n  white-space:nowrap; font-size:12.5px; font-weight:500; line-height:1;\n  padding:5px 10px; background:rgba(255,255,255,0.93);\n  border:1px solid rgba(28,36,75,0.16); border-radius:999px;\n  color:#1C244B; will-change:transform;\n}\n.ols-ptsm-001 .ptsm-lab.l-part{font-weight:500;}\n.ols-ptsm-001 .ptsm-lab.l-msg{font-weight:600; border-color:rgba(28,36,75,0.32);}\n.ols-ptsm-001 .ptsm-lab.l-pos{font-weight:600; border-color:rgba(212,58,50,0.7); color:#b02a24;}\n.ols-ptsm-001 .ptsm-lab.l-neg{font-weight:600; border-color:rgba(37,99,235,0.6); color:#1d4fb8;}\n.ols-ptsm-001 .ptsm-lab.l-e{font-size:11.5px; font-weight:600; border-color:rgba(214,150,24,0.8); color:#8a6410;}\n.ols-ptsm-001 .ptsm-lab.l-ok{font-weight:600; border-color:rgba(47,158,87,0.8); color:#1f7a3a;}\n.ols-ptsm-001 .ptsm-lab.l-soft{font-size:11.5px; color:#2f5f9a; border-color:rgba(70,125,190,0.45);}\n.ols-ptsm-001 .ptsm-lab.l-sm{font-size:11px; padding:4px 8px;}\n\n.ols-ptsm-001 .ptsm-caption{\n  position:absolute; left:14px; top:14px; max-width:60%;\n  font-size:12px; font-weight:500; color:#4a5270; line-height:1.35;\n  background:rgba(255,255,255,0.92); padding:6px 12px;\n  border-radius:14px; border:1px solid rgba(28,36,75,0.12);\n}\n.ols-ptsm-001 .ptsm-hint{\n  position:absolute; right:14px; top:14px;\n  font-size:11.5px; font-weight:400; color:#8b92a8;\n  background:rgba(255,255,255,0.9); padding:5px 11px;\n  border-radius:999px; border:1px solid rgba(28,36,75,0.10);\n}\n.ols-ptsm-001 .ptsm-badges{\n  position:absolute; right:14px; bottom:14px; max-width:58%;\n  display:flex; flex-direction:column; align-items:flex-end; gap:6px;\n}\n.ols-ptsm-001 .ptsm-badge{\n  font-size:12px; font-weight:500; color:#1C244B; line-height:1.35; text-align:right;\n  background:rgba(255,255,255,0.95); padding:5px 12px;\n  border-radius:14px; border:1px solid rgba(28,36,75,0.22);\n}\n.ols-ptsm-001 .ptsm-badge.b-eq{font-size:13.5px; font-weight:600; border-color:rgba(201,150,28,0.75);}\n\n.ols-ptsm-001 .ptsm-controls{margin-top:20px; display:flex; flex-direction:column; gap:12px;}\n.ols-ptsm-001 .ptsm-row{display:flex; align-items:center; gap:10px; flex-wrap:wrap;}\n.ols-ptsm-001 .ptsm-rowlab{font-size:12px; font-weight:500; color:#6b7290; min-width:100px; flex:0 0 auto;}\n\n.ols-ptsm-001 .ptsm-seg{\n  display:inline-flex; border:1px solid rgba(28,36,75,0.16);\n  border-radius:12px; overflow:hidden; background:#fbfbfd; flex-wrap:wrap;\n}\n.ols-ptsm-001 .ptsm-seg button{\n  font-family:inherit; font-size:14px; font-weight:500; color:#3c4463;\n  background:transparent; border:0; border-right:1px solid rgba(28,36,75,0.12);\n  padding:9px 18px; cursor:pointer; transition:background .15s, color .15s;\n  display:inline-flex; align-items:center;\n}\n.ols-ptsm-001 .ptsm-seg button:last-child{border-right:0;}\n.ols-ptsm-001 .ptsm-seg button:hover{background:rgba(37,99,235,0.06);}\n.ols-ptsm-001 .ptsm-seg button[aria-pressed=\"true\"]{background:#2563eb; color:#fff;}\n.ols-ptsm-001 .ptsm-seg button:focus-visible{outline:2px solid #2563eb; outline-offset:-2px;}\n.ols-ptsm-001 .ptsm-seg button .ptsm-n{display:inline-flex; align-items:center; justify-content:center; width:20px; height:20px; margin-right:9px; border-radius:50%; font-size:11px; font-weight:600; background:rgba(37,99,235,0.10); color:#2563eb; flex:0 0 auto;}\n.ols-ptsm-001 .ptsm-seg button[aria-pressed=\"true\"] .ptsm-n{background:#ffffff; color:#2563eb;}\n\n.ols-ptsm-001 .ptsm-pill{\n  font-family:inherit; font-size:13px; font-weight:500; color:#3c4463;\n  background:#fbfbfd; border:1px solid rgba(28,36,75,0.16);\n  border-radius:999px; padding:8px 16px; cursor:pointer;\n  display:inline-flex; align-items:center; gap:8px;\n  transition:background .15s, border-color .15s, color .15s;\n}\n.ols-ptsm-001 .ptsm-pill:hover{border-color:rgba(37,99,235,0.4);}\n.ols-ptsm-001 .ptsm-pill:focus-visible{outline:2px solid #2563eb; outline-offset:2px;}\n\n.ols-ptsm-001 .ptsm-info{\n  margin-top:22px; padding:22px 24px;\n  border:1px solid rgba(28,36,75,0.12); border-radius:16px; background:#fbfbfd;\n}\n.ols-ptsm-001 .ptsm-info h3{margin:0 0 8px; font-size:15.5px; font-weight:600; color:#1C244B;}\n.ols-ptsm-001 .ptsm-info p{margin:0; font-size:14px; line-height:1.68; font-weight:300; color:#41496a; max-width:74ch;}\n.ols-ptsm-001 .ptsm-facts{\n  margin-top:16px; display:flex; gap:26px; flex-wrap:wrap;\n  padding-top:16px; border-top:1px solid rgba(28,36,75,0.10);\n}\n.ols-ptsm-001 .ptsm-fact{min-width:110px;}\n.ols-ptsm-001 .ptsm-fact span{display:block; font-size:11.5px; color:#7d8399; font-weight:400; margin-bottom:3px;}\n.ols-ptsm-001 .ptsm-fact strong{display:block; font-size:15px; font-weight:600; color:#1C244B;}\n\n.ols-ptsm-001 .ptsm-key{\n  margin-top:16px; display:flex; gap:20px; flex-wrap:wrap;\n  font-size:12.5px; font-weight:400; color:#5a6180;\n}\n.ols-ptsm-001 .ptsm-key i{\n  display:inline-block; width:13px; height:13px; border-radius:50%;\n  margin-right:7px; vertical-align:-2px; border:1px solid rgba(28,36,75,0.18);\n}\n\n@media (max-width:760px){\n  .ols-ptsm-001{padding:26px; border-radius:22px;}\n  .ols-ptsm-001 h2.ptsm-title{font-size:20.5px;}\n  .ols-ptsm-001 p.ptsm-sub{font-size:13.5px;}\n  .ols-ptsm-001 .ptsm-stage{height:440px;}\n  .ols-ptsm-001 .ptsm-rowlab{min-width:100%;}\n  .ols-ptsm-001 .ptsm-seg button{padding:9px 13px; font-size:13px;}\n  .ols-ptsm-001 .ptsm-lab{font-size:10.5px; padding:4px 8px;}\n  .ols-ptsm-001 .ptsm-lab.l-e,.ols-ptsm-001 .ptsm-lab.l-soft,.ols-ptsm-001 .ptsm-lab.l-sm{font-size:9.5px; padding:3px 7px;}\n  .ols-ptsm-001 .ptsm-caption{font-size:10.5px; padding:5px 9px; max-width:64%;}\n  .ols-ptsm-001 .ptsm-badge{font-size:10.5px; padding:4px 9px;}\n  .ols-ptsm-001 .ptsm-badge.b-eq{font-size:11px;}\n  .ols-ptsm-001 .ptsm-badges{max-width:calc(100% - 28px);}\n  .ols-ptsm-001 .ptsm-info{padding:18px;}\n}\n\/* on a phone the caption needs the full top row, so the drag hint goes *\/\n@media (max-width:480px){\n  .ols-ptsm-001 .ptsm-hint{display:none;}\n  .ols-ptsm-001 .ptsm-caption{max-width:calc(100% - 28px);}\n}\n@media (prefers-reduced-motion:reduce){\n  .ols-ptsm-001 .ptsm-seg button,.ols-ptsm-001 .ptsm-pill{transition:none;}\n}\n\n.ols-cc-ptsm-001{\n  font-family:'Poppins',system-ui,-apple-system,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;\n  margin:10px auto 0; text-align:center; font-size:11px; font-style:italic; color:#aab0c0;\n}\n.ols-cc-ptsm-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-ptsm-001 a:hover{text-decoration:underline;}\n<\/style>\n\n<div class=\"ptsm-head\">\n  <h2 class=\"ptsm-title\">Period 3 Structures and Melting<\/h2>\n  <p class=\"ptsm-sub\">Choose a step to watch each Period 3 structure, then see how much energy each element needs to melt.<\/p>\n<\/div>\n\n<div class=\"ptsm-stage\" id=\"ptsmStage\">\n  <canvas class=\"ptsm-canvas\" id=\"ptsmCanvas\"><\/canvas>\n  <div class=\"ptsm-overlay\" id=\"ptsmOverlay\"><\/div>\n  <div class=\"ptsm-caption\" id=\"ptsmCaption\"><\/div>\n  <div class=\"ptsm-hint\" id=\"ptsmHint\">Drag to rotate<\/div>\n  <div class=\"ptsm-badges\" id=\"ptsmBadges\"><\/div>\n<\/div>\n\n<div class=\"ptsm-controls\">\n  <div class=\"ptsm-row\">\n    <span class=\"ptsm-rowlab\">Step<\/span>\n    <div class=\"ptsm-seg\" role=\"group\" aria-label=\"Step\">\n      <button type=\"button\" data-step=\"1\" aria-pressed=\"true\"><span class=\"ptsm-n\">1<\/span>Na, Mg, Al: metallic<\/button>\n      <button type=\"button\" data-step=\"2\" aria-pressed=\"false\"><span class=\"ptsm-n\">2<\/span>Si: giant covalent<\/button>\n      <button type=\"button\" data-step=\"3\" aria-pressed=\"false\"><span class=\"ptsm-n\">3<\/span>P\u2084, S\u2088, Cl\u2082: simple molecules<\/button>\n      <button type=\"button\" data-step=\"4\" aria-pressed=\"false\"><span class=\"ptsm-n\">4<\/span>Ar: single atoms<\/button>\n      <button type=\"button\" data-step=\"5\" aria-pressed=\"false\"><span class=\"ptsm-n\">5<\/span>Energy to melt<\/button>\n    <\/div>\n  <\/div>\n\n  <div class=\"ptsm-row\">\n    <span class=\"ptsm-rowlab\">View<\/span>\n    <button type=\"button\" class=\"ptsm-pill\" id=\"ptsmResetV\">Reset view<\/button>\n  <\/div>\n<\/div>\n\n<div class=\"ptsm-info\">\n  <h3 id=\"ptsmInfoTitle\"><\/h3>\n  <p id=\"ptsmInfoText\"><\/p>\n  <div class=\"ptsm-facts\" id=\"ptsmFacts\"><\/div>\n  <div class=\"ptsm-key\">\n    <span><i style=\"background:#8c52c4\"><\/i>Na\u207a ion<\/span>\n    <span><i style=\"background:#aaaeb8\"><\/i>Mg\u00b2\u207a \/ Al\u00b3\u207a ion<\/span>\n    <span><i style=\"background:#f0a820\"><\/i>Delocalised electron<\/span>\n    <span><i style=\"background:#c4aa78\"><\/i>Silicon<\/span>\n    <span><i style=\"background:#eb8c28\"><\/i>Phosphorus<\/span>\n    <span><i style=\"background:#e1c328\"><\/i>Sulfur<\/span>\n    <span><i style=\"background:#34aa48\"><\/i>Chlorine<\/span>\n    <span><i style=\"background:#78c8e1\"><\/i>Argon<\/span>\n  <\/div>\n<\/div>\n\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/period3-structures-mp.js?v=20261025p\"><\/script>\n<\/section>\n\n<p class=\"ols-cc-ptsm-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\n\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Order a Period by Melting Temperature<\/h2>\n<p>Rank five Period 2 elements by structure, lowest melting temperature first.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-474\" class=\"h5p-iframe\" data-content-id=\"474\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Periodic Trends Sort: Melting Temperatures Across Period 2\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <div class=\"ols-zoom-card\">\n        <div class=\"ols-zoom-card-image\">\n          <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/fix-14.jpg\" alt=\"Graph of melting and boiling points across Period 3, peaking at silicon\" 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>You need to illustrate periodicity using data, including electronic configurations, atomic radii, melting and boiling temperatures and first ionisation energies.<\/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. Small exceptions occur between Group 2 and Group 3, and between Group 5 and Group 6.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Matching the Argument to the Trend<\/h2>\n<p>Pick the one accurate statement in each round to finish the page.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-789\" class=\"h5p-iframe\" data-content-id=\"789\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Periodic Trends Summary: Which Argument Fits Which Trend\"><\/iframe><\/div><\/div>\n<\/section>\n\n\n\n      \n\n<article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">6<\/div><h2>Common Exam Points<\/h2><\/div>\n        <ul>\n          <li>Across a period, nuclear charge increases while shielding stays similar, so <strong>atomic radius decreases<\/strong>.<\/li>\n          <li>Down a group, the extra shells and extra shielding make atomic radius increase and first ionisation energy decrease.<\/li>\n          <li>Explain the melting temperature trend using <strong>structure and bonding<\/strong>, never ionisation energy.<\/li>\n          <li>Silicon has the highest melting temperature in Period 3 because its giant covalent lattice has many strong covalent bonds to break.<\/li>\n          <li>The melting temperature rises from sodium to aluminium because metallic bonding gets stronger: more delocalised electrons per atom and a smaller, more highly charged ion.<\/li>\n          <li>Among the simple molecular elements, S<sub>8<\/sub> has the most electrons, so it has the strongest London forces and the highest melting temperature.<\/li>\n        <\/ul>\n      <\/article>\n\n      <section class=\"ols-quicksnap-card\">\n        <h2>QuickSnap<\/h2>\n        <p>This text summary condenses the page into the essential exam ideas.<\/p>\n        <ul class=\"ols-quicksnap-list\">\n          <li><strong>Periodicity<\/strong> is the repeating pattern of properties across each period, caused by the repeating pattern of subshell filling.<\/li>\n          <li><strong>Atomic radius<\/strong> decreases across a period and increases down a group.<\/li>\n          <li><strong>First ionisation energy<\/strong> generally increases across a period and decreases down a group, with small dips at Group 3 and Group 6.<\/li>\n          <li><strong>Melting temperatures<\/strong> rise from sodium to silicon, then fall sharply to the simple molecular elements and argon.<\/li>\n        <\/ul>\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 temperatures not follow the same trend as ionisation energy across a period?<\/h3>\n            <p>Melting and boiling temperatures 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      <!-- author card (moved to the end, 10 Oct 2026) -->\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\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 ols-attr-std\" aria-label=\"Copyright notice\">\n<style id=\"ols-attribution-card-css\">.ols-attribution-card.ols-attr-std{background:linear-gradient(135deg,#ffffff,#f8fbff);border:1px solid rgba(28,36,75,0.14);border-radius:28px;box-shadow:0 18px 45px rgba(28,36,75,0.10);padding:34px;margin:24px 0;overflow:hidden;font-family:Poppins,Arial,sans-serif;box-sizing:border-box}.ols-attribution-card.ols-attr-std *{box-sizing:border-box}.ols-attribution-card.ols-attr-std p{margin:0;font-size:14px;line-height:1.65;font-weight:300;color:#667085}.ols-attribution-card.ols-attr-std strong{font-weight:700;color:#1C244B}@media (max-width:760px){.ols-attribution-card.ols-attr-std{padding:24px 18px;border-radius:22px}}<\/style>\n<p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n<\/section>\n\n      <div class=\"ols-image-lightbox\" id=\"olsImageLightboxPeriodicTrends9ch0\" aria-hidden=\"true\" role=\"dialog\" aria-modal=\"true\" aria-label=\"Expanded revision image\">\n        <div class=\"ols-image-lightbox-inner\">\n          <button class=\"ols-image-lightbox-close\" type=\"button\" aria-label=\"Close enlarged image\">\u00d7<\/button>\n          <img decoding=\"async\" class=\"ols-image-lightbox-img\" src=\"\" alt=\"\">\n        <\/div>\n      <\/div>\n\n      <script>\n        (function(){\n          var page = document.querySelector(\".ols-periodic-trends-9ch0-page\");\n          if (!page) return;\n          var lightbox = page.querySelector(\"#olsImageLightboxPeriodicTrends9ch0\");\n          if (!lightbox) return;\n          var lightboxImage = lightbox.querySelector(\".ols-image-lightbox-img\");\n          var closeButton = lightbox.querySelector(\".ols-image-lightbox-close\");\n          var clickableImages = page.querySelectorAll(\"img.ols-lightbox-target\");\n          function openLightbox(image) {\n            lightboxImage.src = image.currentSrc || image.src;\n            lightboxImage.alt = image.alt || \"Expanded revision image\";\n            lightbox.classList.add(\"is-open\");\n            lightbox.setAttribute(\"aria-hidden\", \"false\");\n            if (!document.body.dataset.olsPreviousOverflow) { document.body.dataset.olsPreviousOverflow = document.body.style.overflow || \"default\"; }\n            document.body.style.overflow = \"hidden\";\n          }\n          function closeLightbox() {\n            lightbox.classList.remove(\"is-open\");\n            lightbox.setAttribute(\"aria-hidden\", \"true\");\n            lightboxImage.src = \"\";\n            if (document.body.dataset.olsPreviousOverflow) {\n              document.body.style.overflow = document.body.dataset.olsPreviousOverflow === \"default\" ? \"\" : document.body.dataset.olsPreviousOverflow;\n              delete document.body.dataset.olsPreviousOverflow;\n            }\n          }\n          clickableImages.forEach(function(image){ image.addEventListener(\"click\", function(e){ e.preventDefault(); e.stopPropagation(); openLightbox(image); }); });\n          closeButton.addEventListener(\"click\", closeLightbox);\n          lightbox.addEventListener(\"click\", function(e){ if (e.target === lightbox) closeLightbox(); });\n          document.addEventListener(\"keydown\", function(e){ if (e.key === \"Escape\" && lightbox.classList.contains(\"is-open\")) closeLightbox(); });\n        })();\n      <\/script>\n\n      <script type=\"application\/ld+json\">\n{\n    \"@context\": \"https:\/\/schema.org\",\n    \"@graph\": [\n        {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/periodic-trends\/#webpage\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/periodic-trends\/\",\n            \"name\": \"Periodic Trends | Edexcel A Level Chemistry Revision Notes\",\n            \"description\": \"Edexcel A Level Chemistry revision notes on periodicity: atomic radius and ionisation energy trends across periods and down groups, melting and boiling point trends across Period 3, and using data to illustrate periodic properties.\",\n            \"inLanguage\": \"en-GB\",\n            \"isPartOf\": {\n                \"@type\": \"WebSite\",\n                \"name\": \"Online Learning System\",\n                \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/\"\n            },\n            \"author\": {\n                \"@type\": \"Person\",\n                \"name\": \"Dr. Mohammed Al-Fatah\",\n                \"url\": \"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\"\n            },\n            \"publisher\": {\n                \"@type\": \"Organization\",\n                \"name\": \"Online Learning System\",\n                \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/\"\n            }\n        },\n        {\n            \"@type\": \"BreadcrumbList\",\n            \"itemListElement\": [\n                {\n                    \"@type\": \"ListItem\",\n                    \"position\": 1,\n                    \"name\": \"Revision Notes\",\n                    \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\"\n                },\n                {\n                    \"@type\": \"ListItem\",\n                    \"position\": 2,\n                    \"name\": \"A Level Chemistry\",\n                    \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\"\n                },\n                {\n                    \"@type\": \"ListItem\",\n                    \"position\": 3,\n                    \"name\": \"Edexcel\",\n                    \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\"\n                },\n                {\n                    \"@type\": \"ListItem\",\n                    \"position\": 4,\n                    \"name\": \"Topic 1 Atomic Structure and The Periodic Table\",\n                    \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/\"\n                },\n                {\n                    \"@type\": \"ListItem\",\n                    \"position\": 5,\n                    \"name\": \"Periodic Trends\",\n                    \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/periodic-trends\/\"\n                }\n            ]\n        },\n        {\n            \"@type\": \"FAQPage\",\n            \"mainEntity\": [\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"What is periodicity?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"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.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"Why does atomic radius decrease across a period?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"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.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"Why do melting and boiling temperatures not follow the same trend as ionisation energy across a period?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"Melting and boiling temperatures 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.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"Why does first ionisation energy generally increase across a period?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"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.\"\n                    }\n                },\n                {\n                    \"@type\": \"Question\",\n                    \"name\": \"Why does first ionisation energy decrease down a group?\",\n                    \"acceptedAnswer\": {\n                        \"@type\": \"Answer\",\n                        \"text\": \"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.\"\n                    }\n                }\n            ]\n        }\n    ]\n}\n<\/script>\n    <\/main>\n  <\/div>\n<\/section>\n","protected":false},"excerpt":{"rendered":"<p>Revision Notes \/ A Level Chemistry \/ Edexcel \/ Topic 1 Atomic Structure &amp; The Periodic Table \/ Periodic Trends Periodic Trends A concise revision guide to periodicity: atomic radius and ionisation energy trends across a period and down a group, melting and boiling temperature trends across Period 3, and how physical properties link to [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":4497,"menu_order":4,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-4517","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4517","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/comments?post=4517"}],"version-history":[{"count":2,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4517\/revisions"}],"predecessor-version":[{"id":24858,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4517\/revisions\/24858"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4497"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=4517"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}