{"id":7978,"date":"2026-09-14T22:00:09","date_gmt":"2026-09-14T21:00:09","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/atomic-and-ionic-radii\/"},"modified":"2026-09-22T16:33:36","modified_gmt":"2026-09-22T15:33:36","slug":"atomic-and-ionic-radii","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/atomic-and-ionic-radii\/","title":{"rendered":"Atomic and Ionic Radii"},"content":{"rendered":"<script src=\"https:\/\/cdnjs.cloudflare.com\/ajax\/libs\/three.js\/r128\/three.min.js\"><\/script>\n\n<section class=\"ols-revision-page ols-atomic-structure-9ch0-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --soft-orange: #fff7ed;\n      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align-items: flex-start; padding: 22px 18px; border-radius: 22px; }\n      .ols-author-avatar-img { width: 72px; height: 72px; }\n      .ols-author-title { font-size: 24px; }\n      .ols-author-description { font-size: 15px; }\n      .ols-left-numbers { font-size: 26px; }\n      .ols-symbol-core { font-size: 52px; }\n      .ols-symbol-labels { font-size: 13px; }\n    }\n  \n    .ols-figure-placeholder .ols-placeholder-box { border: 2px dashed #c9973a; background: #fffaf0; border-radius: 16px; padding: 26px 22px; font-weight: 700; color: #7a4b12; text-align: center; line-height: 1.6; }\n    .ols-figure-placeholder .ols-figure-image { background: transparent; }\n    .ols-figure-placeholder { background: #ffffff; border: 1px solid rgba(28, 36, 75, 0.12); border-radius: 22px; padding: 14px; margin: 18px 0 6px; }\n    .ols-figure-placeholder .ols-figure-caption p { margin: 10px 0 0; font-size: 14px; color: #667085; text-align: center; }\n<\/style>\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>Cambridge International AS Level Chemistry<\/p>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>Topic 1 Atomic Structure<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/\">Topic overview<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/atomic-structure\/\">1.1 \/ 1.2 Atomic Structure and Isotopes<\/a><\/li>\n<li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/charged-particles-in-electric-fields\/\">1.1 Charged Particles in Electric Fields<\/a><\/li>\n<li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/atomic-and-ionic-radii\/\">1.1 Atomic and Ionic Radii<\/a><\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/mass-spectrometry\/\">1.2 Mass Spectrometry<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/mass-spectrometry\/the-mass-spectrometer\/\">The Mass Spectrometer<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/mass-spectrometry\/ram-calculations\/\">RAM Calculations<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/mass-spectrometry\/predicting-diatomic-mass-spectra\/\">Predicting Diatomic Mass Spectra<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/\">Identifying Compounds from Mass Spectra<\/a><\/li>\n        <\/ul>\n      <\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/electron-configuration\/\">1.3 Electron Configuration<\/a><\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/ionisation-energy\/\">1.4 Ionisation Energy<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/ionisation-energy\/introduction-to-ionisation-energy\/\">Introduction to Ionisation Energy<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/ionisation-energy\/successive-ionisation-energies\/\">Successive Ionisation Energies<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/ionisation-energy\/trends-in-a-period\/\">Trends in a Period<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/ionisation-energy\/trends-in-a-group\/\">Trends in a Group<\/a><\/li>\n        <\/ul>\n      <\/li>\n    <\/ul>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>Other Topics<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-3-chemical-bonding\/\">Topic 3 Chemical Bonding<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-4-states-of-matter\/\">Topic 4 States of Matter<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-9-the-periodic-table-chemical-periodicity\/\">Topic 9 Chemical Periodicity<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-13-an-introduction-to-as-level-organic-chemistry\/\">Topic 13 Introduction to Organic Chemistry<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-14-hydrocarbons\/\">Topic 14 Hydrocarbons<\/a><\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\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 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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\/cie\/\">Cambridge International (CIE)<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/\">Topic 1 Atomic Structure<\/a> \/\n<span>Atomic and Ionic Radii<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Atomic and Ionic Radii<\/h1>\n        <p class=\"ols-page-intro\">A concise Cambridge International AS Level Chemistry revision guide to how atomic radius and ionic radius change across a period and down a group, why positive ions are smaller than their atoms and negative ions larger, and the isoelectronic ions of Period 3 (1.1.7 and 9.1.1).<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">AS Level<\/div>\n<div class=\"ols-badge\">Topic 1: Atomic Structure<\/div>\n<div class=\"ols-badge\">9701 Papers 1 and 2<\/div>\n<\/div>\n\n        <div class=\"ols-author\">\n        \n            <img decoding=\"async\"\n              class=\"ols-author-avatar-img\"\n              src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n              alt=\"Dr. Mohammed Al-Fatah\"\n            >\n        \n            <div class=\"ols-author-content\">\n        \n              <h2 class=\"ols-author-title\">\n                Written by: Dr. Mohammed Al-Fatah\n              <\/h2>\n        \n              <p class=\"ols-author-description\">\n                Chemistry specialist revision notes for A Level Chemistry.\n              <\/p>\n        \n              <a class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\n        \n                <svg class=\"ols-linkedin-icon\" viewBox=\"0 0 24 24\" fill=\"currentColor\" aria-hidden=\"true\">\n                  <path d=\"M4.98 3.5C4.98 4.88 3.86 6 2.48 6S0 4.88 0 3.5 1.12 1 2.48 1s2.5 1.12 2.5 2.5zM.5 8h4V24h-4V8zm7 0h3.8v2.2h.1c.5-.9 1.8-2.2 3.9-2.2 4.2 0 5 2.8 5 6.4V24h-4v-7.6c0-1.8 0-4.2-2.6-4.2s-3 2-3 4v7.8h-4V8z\"\/>\n                <\/svg>\n        \n                View LinkedIn Profile\n        \n              <\/a>\n        \n            <\/div>\n        \n          <\/div>\n      <\/header>\n\n      <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: Shells, Size and Forming Ions<\/h2>\n<p>Before you start, check that you can count occupied shells and say what an atom loses or gains when it forms an ion.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"821\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>What Atomic Radius Means<\/h2>\n<\/div>\n<p>An atom has no hard edge, so its size is defined by measuring the distance between two nuclei that are bonded together and halving it. For most non-metals the <strong>covalent radius<\/strong> (half the distance between two bonded atoms in a molecule) is used; for metals the <strong>metallic radius<\/strong> (half the distance between neighbouring ions in the metal lattice) is used. Values are given in nanometres or picometres: sodium is about 0.19 nm, chlorine about 0.10 nm.<\/p>\n<p>Two factors set the size of an atom: how many <strong>shells<\/strong> of electrons it has, and how strongly the outer shell is pulled in by the <strong>nuclear charge<\/strong> after allowing for <strong>shielding<\/strong> by the inner shells.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> More shells: bigger atom. Higher nuclear charge with the same shielding: smaller atom.<\/p>\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: Halve the Distance<\/h2>\n<p>Work each radius out on paper from the measured distance between the nuclei, then type it in.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-485\" class=\"h5p-iframe\" data-content-id=\"485\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Atomic and Ionic Radii Blanks: Halving the Distance Between Two Nuclei\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>Atomic Radius Across a Period<\/h2>\n<\/div>\n<p>Across Period 3 from sodium to chlorine the atomic radius <strong>decreases<\/strong>. Each element adds one proton to the nucleus and one electron to the <strong>same outer shell<\/strong> (the third shell). The inner shells that do the shielding are unchanged, so the outer electrons feel a steadily larger effective nuclear charge and are pulled closer.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Element<\/th><th>Na<\/th><th>Mg<\/th><th>Al<\/th><th>Si<\/th><th>P<\/th><th>S<\/th><th>Cl<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Atomic radius \/ nm<\/strong><\/td><td>0.191<\/td><td>0.160<\/td><td>0.143<\/td><td>0.118<\/td><td>0.110<\/td><td>0.104<\/td><td>0.099<\/td><\/tr>\n<tr><td><strong>Protons<\/strong><\/td><td>11<\/td><td>12<\/td><td>13<\/td><td>14<\/td><td>15<\/td><td>16<\/td><td>17<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Argon is left out of the comparison because as a noble gas it forms no bonds, so its radius is measured differently (a van der Waals radius) and is not comparable.<\/p>\n<div class=\"ols-zoom-card\">\n<div class=\"ols-figure-card\">\n<div class=\"ols-figure-image\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/fix-58.jpg\" alt=\"Bar chart of atomic radius across Period 3, Na 0.191 nm falling to Cl 0.099 nm, with aluminium at 0.143 nm\"><\/div>\n<div class=\"ols-figure-caption\"><p>Atomic radius across Period 3 from sodium to chlorine<\/p><\/div>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Atomic radius falls across Period 3 as nuclear charge rises with no extra shielding.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Across a period the atomic radius decreases because the nuclear charge increases while the electrons are added to the same shell, so shielding is almost constant and the outer electrons are attracted more strongly.<\/p>\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: The Odd Value for Neon<\/h2>\n<p>Decide why one figure in the data book does not fit the pattern of the others.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-487\" class=\"h5p-iframe\" data-content-id=\"487\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Atomic and Ionic Radii MCQ: The Radius a Data Book Quotes for Neon\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>Atomic Radius Down a Group<\/h2>\n<\/div>\n<p>Down any group the atomic radius <strong>increases<\/strong>. Each successive element has one more occupied shell, so its outer electrons are further from the nucleus. The extra inner shells also add <strong>shielding<\/strong>, which more than cancels the effect of the larger nuclear charge.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Group 1<\/th><th>Li<\/th><th>Na<\/th><th>K<\/th><th>Rb<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Atomic radius \/ nm<\/strong><\/td><td>0.152<\/td><td>0.186<\/td><td>0.231<\/td><td>0.244<\/td><\/tr>\n<tr><td><strong>Occupied shells<\/strong><\/td><td>2<\/td><td>3<\/td><td>4<\/td><td>5<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Down a group the atomic radius increases because each element has an extra shell of electrons and more shielding, which outweighs the increase in nuclear charge.<\/p>\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: Do Extra Protons Make an Atom Bigger?<\/h2>\n<p>Judge the reason given, not just the claim, then read the feedback.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-822\" class=\"h5p-iframe\" data-content-id=\"822\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Atomic and Ionic Radii True or False: More Protons in the Bigger Atom\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Ionic Radius: Cations Shrink, Anions Grow<\/h2>\n<\/div>\n<p>When an atom forms a <strong>positive ion<\/strong> it loses its outer electrons, usually the whole outer shell. The ion has one shell fewer than the atom, and the remaining electrons are held by the same nuclear charge with less repulsion between them, so a <strong>cation is much smaller than its atom<\/strong>: Na 0.191 nm but Na<sup>+<\/sup> 0.102 nm.<\/p>\n<p>When an atom forms a <strong>negative ion<\/strong> it gains electrons into the same outer shell. 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border-radius:3px;\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-rad-001{padding:26px; border-radius:22px;}\n  .ols-rad-001 h2.rad-title{font-size:20.5px;}\n  .ols-rad-001 p.rad-sub{font-size:13.5px;}\n  .ols-rad-001 .rad-stage{height:400px;}\n  .ols-rad-001 .rad-rowlab{min-width:100%;}\n  .ols-rad-001 .rad-seg button{padding:9px 12px; font-size:12.5px;}\n  .ols-rad-001 .rad-caption{font-size:10.5px; padding:5px 9px; max-width:68%;}\n  .ols-rad-001 .rad-info{padding:18px;}\n}\n@media (prefers-reduced-motion:reduce){\n  .ols-rad-001 .rad-seg button,.ols-rad-001 .rad-pill{transition:none;}\n}\n\n.ols-cc-rad-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-rad-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-rad-001 a:hover{text-decoration:underline;}\n<\/style>\n\n<div class=\"rad-head\">\n  <h2 class=\"rad-title\">Atomic and Ionic Radii Across Period 3 and Down Group 1<\/h2>\n  <p class=\"rad-sub\">Every sphere is drawn to scale against the 0.1 nm ruler, so the sizes can be compared directly. Drag to rotate, scroll or pinch to zoom.<\/p>\n<\/div>\n\n<div class=\"rad-stage\" id=\"radStage\">\n  <canvas class=\"rad-canvas\" id=\"radCanvas\"><\/canvas>\n  <div class=\"rad-caption\" id=\"radCaption\"><\/div>\n  <div class=\"rad-hint\" id=\"radHint\">Drag to rotate<\/div>\n<\/div>\n\n<div class=\"rad-controls\">\n  <div class=\"rad-row\">\n    <span class=\"rad-rowlab\">View<\/span>\n    <div class=\"rad-seg\" role=\"group\" aria-label=\"View\">\n      <button type=\"button\" data-v=\"p3\" aria-pressed=\"true\">Period 3<\/button>\n      <button type=\"button\" data-v=\"iso\" aria-pressed=\"false\">Isoelectronic ions<\/button>\n      <button type=\"button\" data-v=\"g1\" aria-pressed=\"false\">Down Group 1<\/button>\n    <\/div>\n  <\/div>\n\n  <div class=\"rad-row\">\n    <span class=\"rad-rowlab\">Show<\/span>\n    <button type=\"button\" class=\"rad-pill\" id=\"radTogIon\" aria-pressed=\"false\"><i class=\"dot\"><\/i>Show ions<\/button>\n    <button type=\"button\" class=\"rad-pill\" id=\"radTogLab\" aria-pressed=\"true\"><i class=\"dot\"><\/i>Labels<\/button>\n    <button type=\"button\" class=\"rad-pill\" id=\"radTogNuc\" aria-pressed=\"false\"><i class=\"dot\"><\/i>Nucleus<\/button>\n  <\/div>\n\n  <div class=\"rad-row\">\n    <span class=\"rad-rowlab\">Animate<\/span>\n    <button type=\"button\" class=\"rad-pill act\" id=\"radPlay\">Shrink with nuclear charge<\/button>\n    <button type=\"button\" class=\"rad-pill\" id=\"radResetA\">Reset animation<\/button>\n  <\/div>\n\n  <div class=\"rad-row\">\n    <span class=\"rad-rowlab\">Motion<\/span>\n    <button type=\"button\" class=\"rad-pill\" id=\"radSpin\" aria-pressed=\"false\"><i class=\"dot\"><\/i>Rotation<\/button>\n    <button type=\"button\" class=\"rad-pill\" id=\"radResetV\">Reset view<\/button>\n  <\/div>\n<\/div>\n\n<div class=\"rad-info\">\n  <h3 id=\"radInfoTitle\"><\/h3>\n  <p id=\"radInfoText\"><\/p>\n  <div class=\"rad-facts\" id=\"radFacts\"><\/div>\n  <div class=\"rad-key\" id=\"radKey\"><\/div>\n<\/div>\n<\/section>\n\n<p class=\"ols-cc-rad-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\n\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/atomic-radii.js\"><\/script>\n\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Losing a shell makes a cation small; adding electrons to a shell that is already there makes an anion large.<\/p>\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: Atom Against Ion<\/h2>\n<p>Five quick comparisons between an atom and an ion of the same element.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-486\" class=\"h5p-iframe\" data-content-id=\"486\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Atomic and Ionic Radii Quick Fire: The Atom or Its Own Ion?\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card orange\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>The Isoelectronic Ions of Period 3<\/h2>\n<\/div>\n<p>The ions Na<sup>+<\/sup>, Mg<sup>2+<\/sup>, Al<sup>3+<\/sup>, P<sup>3\u2212<\/sup>, S<sup>2\u2212<\/sup> and Cl<sup>\u2212<\/sup> are <strong>isoelectronic<\/strong>: every one of them has exactly ten electrons, the configuration 1s<sup>2<\/sup> 2s<sup>2<\/sup> 2p<sup>6<\/sup> of neon. With identical electron arrangements, only the nuclear charge differs, so the ionic radius falls steadily as the number of protons rises.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Ion<\/th><th>P<sup>3\u2212<\/sup><\/th><th>S<sup>2\u2212<\/sup><\/th><th>Cl<sup>\u2212<\/sup><\/th><th>Na<sup>+<\/sup><\/th><th>Mg<sup>2+<\/sup><\/th><th>Al<sup>3+<\/sup><\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Protons<\/strong><\/td><td>15<\/td><td>16<\/td><td>17<\/td><td>11<\/td><td>12<\/td><td>13<\/td><\/tr>\n<tr><td><strong>Electrons<\/strong><\/td><td>18<\/td><td>18<\/td><td>18<\/td><td>10<\/td><td>10<\/td><td>10<\/td><\/tr>\n<tr><td><strong>Ionic radius \/ nm<\/strong><\/td><td>0.212<\/td><td>0.184<\/td><td>0.181<\/td><td>0.102<\/td><td>0.072<\/td><td>0.054<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Strictly there are two isoelectronic series in Period 3: the cations (ten electrons, like neon) and the anions (eighteen electrons, like argon). Within each series the radius falls as the proton number rises. Across the whole period the ionic radius therefore <strong>falls from Na<sup>+<\/sup> to Al<sup>3+<\/sup>, jumps up sharply at P<sup>3\u2212<\/sup><\/strong> (an extra shell of electrons), then <strong>falls again to Cl<sup>\u2212<\/sup><\/strong>. This is the pattern Cambridge means by the periodicity of ionic radius in 9.1.1.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Na\u207a, Mg\u00b2\u207a and Al\u00b3\u207a are isoelectronic; the ionic radius decreases from Na\u207a to Al\u00b3\u207a because the nuclear charge increases while the number of electrons and the shielding stay the same.<\/p>\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: Order the Ten-Electron Ions<\/h2>\n<p>Put the six ions in order of radius, largest at the top.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-823\" class=\"h5p-iframe\" data-content-id=\"823\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Atomic and Ionic Radii Sort: A Series of Ten-Electron Ions\"><\/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: Explain Two Comparisons<\/h2>\n<p>Write a short explanation, then compare it with the mark points and the model answer.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-488\" class=\"h5p-iframe\" data-content-id=\"488\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Atomic and Ionic Radii Explain: A Sodium Ion Beside a Fluoride Ion\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Common Exam Mistakes<\/h2>\n<\/div>\n<ul>\n<li>Explaining the trend across a period by &#8220;more electrons&#8221;. The extra electrons are in the same shell; the argument is about nuclear charge and constant shielding.<\/li>\n<li>Saying a sodium ion is bigger than a sodium atom &#8220;because it is charged&#8221;. It has lost a whole shell, so it is much smaller.<\/li>\n<li>Treating Cl<sup>\u2212<\/sup> as smaller than Cl because chlorine is &#8220;at the end of the period&#8221;. The anion has gained an electron and is nearly twice the size of the atom.<\/li>\n<li>Forgetting the jump between Al<sup>3+<\/sup> and P<sup>3\u2212<\/sup>. The anions have an extra shell, so the period&#8217;s ionic radii are not one smooth curve.<\/li>\n<\/ul>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Atomic radius falls across a period and rises down a group; cations are smaller and anions larger than their atoms; within an isoelectronic series the radius falls as nuclear charge rises.<\/p>\n<\/div>\n<\/article>\n\n<section class=\"ols-related-card\">\n        <h2>Related Atomic Structure Revision Notes<\/h2>\n        <p>Continue through Topic 1 by linking atomic structure to mass spectrometry, electron configuration and ionisation energy.<\/p>\n\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/mass-spectrometry\/\">Mass Spectrometry<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/electron-configuration\/\">Electron Configuration<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/cie\/topic-1-atomic-structure\/ionisation-energy\/\">Ionisation Energy<\/a>\n        <\/div>\n      <\/section>\n\n      <!-- OLS Author Copyright Footprint \/ Attribution Card -->\n      <section class=\"ols-course-cta-atomic\" id=\"olsCourseCtaAtomic001\">\r\n  <style>\r\n    .ols-course-cta-atomic,\r\n    .ols-course-cta-atomic * {\r\n      box-sizing: border-box;\r\n    }\r\n\r\n    .ols-course-cta-atomic {\r\n      --navy: #1C244B;\r\n      --blue: #2563eb;\r\n      --body-text: #1f2937;\r\n      --grey-text: #667085;\r\n      --border: rgba(28, 36, 75, 0.14);\r\n      --shadow: 0 18px 45px rgba(28, 36, 75, 0.12);\r\n      --inner-shadow: 0 10px 26px rgba(28, 36, 75, 0.08);\r\n\r\n     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.ols-animation-pause-button {\r\n      position: absolute;\r\n      left: 16px;\r\n      bottom: 16px;\r\n      z-index: 7;\r\n      display: none;\r\n      align-items: center;\r\n      justify-content: center;\r\n      min-width: 92px;\r\n      padding: 10px 16px;\r\n      border: 0;\r\n      border-radius: 999px;\r\n      background: rgba(28, 36, 75, 0.92);\r\n      color: #ffffff;\r\n      font-family: Poppins, Arial, sans-serif;\r\n      font-size: 14px;\r\n      line-height: 1.2;\r\n      font-weight: 800;\r\n      cursor: pointer;\r\n      box-shadow: 0 12px 28px rgba(28, 36, 75, 0.24);\r\n      transition:\r\n        transform 0.2s ease,\r\n        background 0.2s ease,\r\n        box-shadow 0.2s ease;\r\n    }\r\n\r\n    .ols-course-cta-atomic .ols-animation-pause-button:hover {\r\n      transform: translateY(-2px);\r\n      background: var(--blue);\r\n      box-shadow: 0 16px 34px rgba(37, 99, 235, 0.28);\r\n    }\r\n\r\n    .ols-course-cta-atomic .ols-animation-pause-button.is-visible {\r\n      display: inline-flex;\r\n    }\r\n\r\n    @keyframes olsAnimationPlayPulse001 {\r\n      0% {\r\n        box-shadow:\r\n          0 18px 40px rgba(28, 36, 75, 0.30),\r\n          0 0 0 0 rgba(255, 255, 255, 0.40);\r\n      }\r\n\r\n      70% {\r\n        box-shadow:\r\n          0 18px 40px rgba(28, 36, 75, 0.30),\r\n          0 0 0 18px rgba(255, 255, 255, 0);\r\n      }\r\n\r\n      100% {\r\n        box-shadow:\r\n          0 18px 40px rgba(28, 36, 75, 0.30),\r\n          0 0 0 0 rgba(255, 255, 255, 0);\r\n      }\r\n    }\r\n\r\n    .ols-course-cta-atomic .ols-course-video-status {\r\n      margin: 14px 0 0;\r\n      text-align: center;\r\n      color: var(--grey-text);\r\n      font-size: 13px;\r\n      line-height: 1.5;\r\n      font-weight: 500;\r\n    }\r\n\r\n    .ols-course-cta-atomic .ols-course-cta-bottom {\r\n      display: flex;\r\n      justify-content: center;\r\n      padding-top: 22px;\r\n      border-top: 1px solid var(--border);\r\n    }\r\n\r\n    .ols-course-cta-atomic .ols-course-button {\r\n      display: inline-flex;\r\n      align-items: center;\r\n      justify-content: center;\r\n      padding: 15px 28px;\r\n      border-radius: 999px;\r\n      background: var(--navy);\r\n      color: #ffffff;\r\n      text-decoration: none;\r\n      font-size: 16px;\r\n      line-height: 1.2;\r\n      font-weight: 800;\r\n      box-shadow: 0 12px 26px rgba(28, 36, 75, 0.18);\r\n      transition:\r\n        transform 0.2s ease,\r\n        background 0.2s ease,\r\n        box-shadow 0.2s ease;\r\n    }\r\n\r\n    .ols-course-cta-atomic .ols-course-button:hover {\r\n      transform: translateY(-2px);\r\n      background: var(--blue);\r\n      color: #ffffff;\r\n      box-shadow: 0 16px 32px rgba(37, 99, 235, 0.24);\r\n    }\r\n\r\n    .ols-course-cta-atomic .ols-course-button-top {\r\n      flex-shrink: 0;\r\n      padding: 12px 22px;\r\n      font-size: 15px;\r\n    }\r\n\r\n    @media (max-width: 900px) {\r\n      .ols-course-cta-atomic .ols-course-cta-top {\r\n        grid-template-columns: 1fr;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-course-cta-image-link {\r\n        max-width: 520px;\r\n        margin: 0 auto;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-course-cta-intro-stats {\r\n        grid-template-columns: 1fr;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-animation-frame-shell {\r\n        height: 520px;\r\n      }\r\n    }\r\n\r\n    @media (max-width: 760px) {\r\n      .ols-course-cta-atomic {\r\n        margin: 26px 0 22px;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-course-cta-card {\r\n        padding: 20px;\r\n        border-radius: 24px;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-course-cta-header-row {\r\n        align-items: stretch;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-course-button-top {\r\n        width: 100%;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-course-cta-stats,\r\n      .ols-course-cta-atomic .ols-course-cta-features {\r\n        grid-template-columns: 1fr;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-course-animation-wrap {\r\n        padding: 0;\r\n        border-radius: 0;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-animation-frame-shell {\r\n        height: 420px;\r\n        border-radius: 18px;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-animation-play-circle {\r\n        width: 76px;\r\n        height: 76px;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-animation-play-icon {\r\n        border-top-width: 14px;\r\n        border-bottom-width: 14px;\r\n        border-left-width: 22px;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-animation-pause-button {\r\n        left: 12px;\r\n        bottom: 12px;\r\n        min-width: 84px;\r\n        padding: 9px 14px;\r\n        font-size: 13px;\r\n      }\r\n\r\n      .ols-course-cta-atomic .ols-course-button {\r\n        width: 100%;\r\n      }\r\n    }\r\n  <\/style>\r\n\r\n  <div class=\"ols-course-cta-card\">\r\n\r\n    <div class=\"ols-course-cta-top\">\r\n\r\n      <a class=\"ols-course-cta-image-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/atomic-structure-and-the-periodic-table-topic-1-cambridge-international\/\" aria-label=\"Open the Cambridge International AS and A Level Chemistry Topics 1 and 9 Atomic Structure and the Periodic Table course page\">\r\n\r\n        <div class=\"ols-course-cta-image\">\r\n          <img decoding=\"async\"\r\n            src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/cambridge-international-a-level-chemistry-topic-1-atomic-structure-interactive-course-banner.jpg\"\r\n            alt=\"Cambridge International AS and A Level Chemistry Topics 1 and 9 Atomic Structure and the Periodic Table interactive course banner\"\r\n          >\r\n        <\/div>\r\n\r\n      <\/a>\r\n\r\n      <div class=\"ols-course-cta-content\">\r\n\r\n        <div class=\"ols-course-cta-header-row\">\r\n\r\n          <div class=\"ols-course-cta-kicker\">\r\n            Cambridge 9701 | Topics 1 and 9 Course\r\n          <\/div>\r\n\r\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-cambridge-international\/\">\r\n            View Course\r\n          <\/a>\r\n\r\n        <\/div>\r\n\r\n        <h2>\r\n          Master Atomic Structure and the Periodic Table for Cambridge International AS &amp; A Level Chemistry\r\n        <\/h2>\r\n\r\n      <\/div>\r\n\r\n    <\/div>\r\n\r\n    <div class=\"ols-course-cta-intro-stats\">\r\n\r\n      <p class=\"ols-course-cta-intro\">\r\n        Continue from these free revision notes into the full Topics 1 and 9 Atomic Structure and the Periodic Table course. The guided video lessons are ready now; the Cambridge International MCQ bank, teacher-marked short-answer questions and KASP spec-point report are being written, and the course opens for enrolment as soon as they are complete.\r\n      <\/p>\r\n\r\n      <div class=\"ols-course-cta-stats\">\r\n\r\n        <div class=\"ols-course-stat\">\r\n          <span>Recorded lessons<\/span>\n          <strong>Coming soon<\/strong>\r\n        <\/div>\r\n\r\n        <div class=\"ols-course-stat\">\r\n          <span>Video lessons<\/span>\n          <strong>Coming soon<\/strong>\r\n        <\/div>\r\n\r\n        <div class=\"ols-course-stat\">\r\n          <span>MCQ practice<\/span>\n          <strong>Coming soon<\/strong>\r\n        <\/div>\r\n\r\n        <div class=\"ols-course-stat\">\r\n          <span>SAQ practice<\/span>\n          <strong>Coming soon<\/strong>\r\n        <\/div>\r\n\r\n      <\/div>\r\n\r\n    <\/div>\r\n\r\n    <div class=\"ols-course-cta-features\">\r\n\r\n      <div class=\"ols-course-feature\">\r\n        <h3>Guided video teaching<\/h3>\r\n        <p>\r\n          Learn the chemistry and exam technique through structured video lessons with worked examples and walkthroughs.\r\n        <\/p>\r\n      <\/div>\r\n\r\n      <div class=\"ols-course-feature\">\r\n        <h3>Instant MCQ feedback<\/h3>\r\n        <p>\r\n          Auto-marked MCQ quizzes provide immediate diagnostic feedback for every answer choice.\r\n        <\/p>\r\n      <\/div>\r\n\r\n      <div class=\"ols-course-feature\">\r\n        <h3>Teacher-marked SAQs<\/h3>\r\n        <p>\r\n          Submit written exam responses and receive chemistry specialist feedback with improvement guidance.\r\n        <\/p>\r\n      <\/div>\r\n\r\n      <div class=\"ols-course-feature\">\r\n        <h3>Progress tracking<\/h3>\r\n        <p>\r\n          Identify strengths and weaknesses across the full Topics 1 and 9 specification with targeted reporting.\r\n        <\/p>\r\n      <\/div>\r\n\r\n    <\/div>\r\n\r\n    <div class=\"ols-course-animation-wrap\">\r\n\r\n      <h3 class=\"ols-course-animation-title\">\r\n        See how the course works\r\n      <\/h3>\r\n\r\n      <div class=\"ols-animation-frame-shell\">\r\n        <iframe\r\n          id=\"olsCourseAnimationFrame001\"\r\n          title=\"OLS course preview animation\"\r\n          loading=\"lazy\"\r\n          referrerpolicy=\"no-referrer\">\r\n        <\/iframe>\r\n\r\n        <button\r\n          class=\"ols-animation-start-overlay\"\r\n          id=\"olsCourseAnimationStart001\"\r\n          type=\"button\"\r\n          aria-label=\"Play OLS course preview animation\">\r\n          <span class=\"ols-animation-start-content\">\r\n            <span class=\"ols-animation-play-circle\" aria-hidden=\"true\">\r\n              <span class=\"ols-animation-play-icon\"><\/span>\r\n            <\/span>\r\n            <span class=\"ols-animation-start-text\">\r\n              Play course preview animation\r\n            <\/span>\r\n          <\/span>\r\n        <\/button>\r\n\r\n        <button\r\n          class=\"ols-animation-pause-button\"\r\n          id=\"olsCourseAnimationPause001\"\r\n          type=\"button\"\r\n          aria-label=\"Pause course preview animation\">\r\n          Pause\r\n        <\/button>\r\n      <\/div>\r\n\r\n      <p class=\"ols-course-video-status\">\r\n        Click play to start the course preview animation.\r\n      <\/p>\r\n\r\n    <\/div>\r\n\r\n    <div class=\"ols-course-cta-bottom\">\r\n\r\n      <a class=\"ols-course-button\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/atomic-structure-and-the-periodic-table-topic-1-cambridge-international\/\">\r\n        View Atomic Structure and the Periodic Table Course\r\n      <\/a>\r\n\r\n    <\/div>\r\n\r\n  <\/div>\r\n\r\n  <template id=\"olsCourseAnimationTemplate001\">\r\n<!DOCTYPE html>\r\n<html lang=\"en\">\r\n<head>\r\n<meta charset=\"UTF-8\">\r\n<meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0\">\r\n<title>OLS Combined Promo Animation<\/title>\r\n\r\n<style>\r\n*{box-sizing:border-box;}\r\n\r\nhtml.ols-animation-paused *,\r\nhtml.ols-animation-paused *::before,\r\nhtml.ols-animation-paused *::after{\r\n  animation-play-state:paused!important;\r\n}\r\n\r\n:root{\r\n  --ols-video-screen-w:1180;\r\n  --ols-video-screen-h:664;\r\n  --ols-video-screen-scale:1;\r\n  --ols-mcq-screen-w:1360;\r\n  --ols-mcq-screen-h:1130;\r\n  --ols-mcq-screen-scale:1;\r\n  --ols-saq-screen-w:1360;\r\n  --ols-saq-screen-h:965;\r\n  --ols-saq-screen-scale:1;\r\n}\r\n\r\nhtml,\r\nbody{\r\n  width:100%;\r\n  height:100%;\r\n}\r\n\r\nbody{\r\n  margin:0;\r\n  overflow:hidden;\r\n  font-family:Poppins,Arial,sans-serif;\r\n  background:#e9efff;\r\n}\r\n\r\n.ols-combined-stage{\r\n  position:relative;\r\n  width:100vw;\r\n  height:100vh;\r\n  overflow:hidden;\r\n  background:\r\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\r\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\r\n}\r\n\r\n.ols-scene{\r\n  position:absolute;\r\n  inset:0;\r\n  width:100vw;\r\n  height:100vh;\r\n  opacity:0;\r\n  visibility:hidden;\r\n  pointer-events:none;\r\n}\r\n\r\n.ols-scene.active{\r\n  opacity:1;\r\n  visibility:visible;\r\n  pointer-events:auto;\r\n}\r\n\r\n.ols-scene.fade-out{\r\n  animation:olsSceneFadeOut 0.85s ease forwards;\r\n}\r\n\r\n@keyframes olsSceneFadeOut{\r\n  to{\r\n    opacity:0;\r\n    visibility:hidden;\r\n  }\r\n}\r\n\r\n.ols-title-cursor{\r\n  display:inline-block;\r\n  width:5px;\r\n  height:0.85em;\r\n  background:#1C244B;\r\n  margin-left:8px;\r\n  transform:translateY(8px);\r\n  animation:olsBlink 0.8s infinite;\r\n}\r\n\r\n.cursor{\r\n  display:inline-block;\r\n  width:3px;\r\n  height:28px;\r\n  background:#1c244b;\r\n  margin-left:3px;\r\n  transform:translateY(5px);\r\n  animation:olsBlink 0.8s infinite;\r\n}\r\n\r\n@keyframes olsBlink{\r\n  0%,45%{opacity:1;}\r\n  46%,100%{opacity:0;}\r\n}\r\n\r\n.ols-video-stage,\r\n.ols-mcq-stage,\r\n.ols-saq-stage{\r\n  width:100vw;\r\n  height:100vh;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n  padding:0;\r\n  overflow:hidden;\r\n  background:\r\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\r\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\r\n}\r\n\r\n.ols-video-title-screen,\r\n.ols-mcq-intro-screen,\r\n.ols-saq-intro{\r\n  position:absolute;\r\n  inset:0;\r\n  z-index:50;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n  background:\r\n    radial-gradient(circle at top left,rgba(70,127,247,0.14),transparent 34%),\r\n    linear-gradient(135deg,#f8fbff 0%,#e9efff 100%);\r\n  opacity:1;\r\n  visibility:visible;\r\n  pointer-events:none;\r\n}\r\n\r\n.ols-video-title-screen.hide{animation:olsVideoTitleFadeOut 0.85s ease forwards;}\r\n.ols-mcq-intro-screen.hide{animation:olsMcqIntroFadeOut 0.85s ease forwards;}\r\n.ols-saq-intro.hide{animation:olsSaqIntroFadeOut 0.85s ease forwards;}\r\n\r\n@keyframes olsVideoTitleFadeOut{to{opacity:0;visibility:hidden;}}\r\n@keyframes olsMcqIntroFadeOut{to{opacity:0;visibility:hidden;}}\r\n@keyframes olsSaqIntroFadeOut{to{opacity:0;visibility:hidden;}}\r\n\r\n.ols-video-title-wrap,\r\n.ols-mcq-intro-title-wrap,\r\n.ols-saq-intro-title-wrap{\r\n  max-width:1250px;\r\n  padding:0 34px;\r\n  text-align:center;\r\n}\r\n\r\n.ols-video-title,\r\n.ols-mcq-intro-title,\r\n.ols-saq-intro-title{\r\n  margin:0;\r\n  font-family:Poppins,Arial,sans-serif;\r\n  font-size:clamp(52px,8vw,124px);\r\n  font-weight:600;\r\n  line-height:1.08;\r\n  color:#1C244B;\r\n  text-shadow:-9px 0 9px rgba(28,36,75,0.16);\r\n  letter-spacing:-0.045em;\r\n}\r\n\r\n#videoTitleText,\r\n#mcqIntroTitleText,\r\n#saqIntroTitleText{\r\n  white-space:pre-wrap;\r\n}\r\n\r\n.ols-video-scene{\r\n  width:100%;\r\n  height:100%;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n  opacity:0;\r\n  visibility:hidden;\r\n}\r\n\r\n.ols-video-scene.show{\r\n  visibility:visible;\r\n  animation:olsVideoSceneIn 1s ease forwards;\r\n}\r\n\r\n@keyframes olsVideoSceneIn{to{opacity:1;}}\r\n\r\n.ols-video-scale-wrap{\r\n  width:calc(var(--ols-video-screen-w) * 1px);\r\n  height:calc(var(--ols-video-screen-h) * 1px);\r\n  transform:scale(var(--ols-video-screen-scale));\r\n  transform-origin:center center;\r\n  display:flex;\r\n  justify-content:center;\r\n  align-items:center;\r\n}\r\n\r\n.ols-video-card{\r\n  width:1180px;\r\n  height:664px;\r\n  border-radius:28px;\r\n  overflow:hidden;\r\n  background:#1C244B;\r\n  box-shadow:0 28px 80px rgba(28,36,75,0.28);\r\n  transform:translateY(24px) scale(0.96);\r\n  opacity:0;\r\n}\r\n\r\n.ols-video-scene.show .ols-video-card{\r\n  animation:olsVideoCardIn 1s cubic-bezier(.18,.89,.32,1.12) forwards;\r\n  animation-delay:0.2s;\r\n}\r\n\r\n@keyframes olsVideoCardIn{\r\n  to{\r\n    transform:translateY(0) 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<section id=\"videoScene\" class=\"ols-video-scene\">\r\n        <div class=\"ols-video-scale-wrap\">\r\n          <div class=\"ols-video-card\">\r\n            <video\r\n              id=\"lessonVideo\"\r\n              src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Virtual-Lesson.mp4\"\r\n              muted\r\n              playsinline\r\n              preload=\"auto\">\r\n            <\/video>\r\n          <\/div>\r\n        <\/div>\r\n      <\/section>\r\n    <\/div>\r\n  <\/section>\r\n\r\n  <section id=\"sceneMcq\" class=\"ols-scene\">\r\n    <div class=\"ols-mcq-stage\">\r\n      <div id=\"mcqIntroScreen\" class=\"ols-mcq-intro-screen\">\r\n        <div class=\"ols-mcq-intro-title-wrap\">\r\n          <h1 class=\"ols-mcq-intro-title\">\r\n            <span id=\"mcqIntroTitleText\"><\/span><span id=\"mcqIntroTitleCursor\" class=\"ols-title-cursor\"><\/span>\r\n          <\/h1>\r\n        <\/div>\r\n      <\/div>\r\n\r\n      <div class=\"ols-mcq-scale-wrap\">\r\n        <main id=\"mcqScreen\" class=\"ols-mcq-screen\">\r\n          <section class=\"mcq-question-area\">\r\n            <p class=\"mcq-question-lead\">Some ionic radii are shown.<\/p>\r\n\r\n            <table class=\"mcq-ionic-table\">\r\n              <thead>\r\n                <tr>\r\n                  <th>Ion<\/th>\r\n                  <th>Ionic radius \/ nm<\/th>\r\n                <\/tr>\r\n              <\/thead>\r\n              <tbody>\r\n                <tr><td>Na<sup>+<\/sup><\/td><td>0.102<\/td><\/tr>\r\n                <tr><td>K<sup>+<\/sup><\/td><td>0.138<\/td><\/tr>\r\n                <tr><td>F<sup>\u2212<\/sup><\/td><td>0.133<\/td><\/tr>\r\n                <tr><td>Cl<sup>\u2212<\/sup><\/td><td>0.180<\/td><\/tr>\r\n              <\/tbody>\r\n            <\/table>\r\n\r\n            <p class=\"mcq-question-main\">Which compound has the strongest ionic bonding?<\/p>\r\n\r\n            <div class=\"mcq-options-wrap\">\r\n              <div id=\"mcqWrongOption\" class=\"mcq-option-row\">\r\n                <span class=\"mcq-radio\"><\/span>\r\n                <span class=\"mcq-radio-ripple\"><\/span>\r\n                <span class=\"mcq-option-label\">sodium chloride<\/span>\r\n\r\n                <span id=\"mcqSpecificFeedback\" class=\"mcq-specific-feedback\">\r\n                  <span id=\"mcqCrossIcon\" class=\"mcq-cross-icon\">\u00d7<\/span>\r\n                  <span class=\"mcq-specific-feedback-text\">\r\n                    <span id=\"mcqSpecificText\"><\/span><span id=\"mcqSpecificCursor\" class=\"cursor mcq-specific-cursor\" style=\"display:none;\"><\/span>\r\n                  <\/span>\r\n                <\/span>\r\n              <\/div>\r\n\r\n              <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span class=\"mcq-option-label\">potassium chloride<\/span><\/div>\r\n              <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span class=\"mcq-option-label\">sodium fluoride<\/span><\/div>\r\n              <div class=\"mcq-option-row\"><span class=\"mcq-radio\"><\/span><span class=\"mcq-radio-ripple\"><\/span><span class=\"mcq-option-label\">potassium fluoride<\/span><\/div>\r\n            <\/div>\r\n\r\n            <button id=\"mcqSubmitButton\" class=\"mcq-submit-button\">Submit answer<\/button>\r\n          <\/section>\r\n\r\n          <section id=\"mcqGeneralFeedback\" class=\"mcq-general-feedback\">\r\n            <span id=\"mcqGeneralText\"><\/span><span id=\"mcqGeneralCursor\" class=\"cursor mcq-general-cursor\" style=\"display:none;\"><\/span>\r\n          <\/section>\r\n        <\/main>\r\n      <\/div>\r\n    <\/div>\r\n  <\/section>\r\n\r\n  <section id=\"sceneSaq\" class=\"ols-scene\">\r\n    <div class=\"ols-saq-stage\">\r\n      <div id=\"saqIntro\" class=\"ols-saq-intro\">\r\n        <div class=\"ols-saq-intro-title-wrap\">\r\n          <h1 class=\"ols-saq-intro-title\">\r\n            <span id=\"saqIntroTitleText\"><\/span><span id=\"saqIntroTitleCursor\" class=\"ols-title-cursor\"><\/span>\r\n          <\/h1>\r\n        <\/div>\r\n      <\/div>\r\n\r\n      <div class=\"ols-saq-scale-wrap\">\r\n        <main id=\"saqScreen\" class=\"ols-saq-screen\">\r\n          <section class=\"saq-question-area\">\r\n            <div class=\"saq-question-text\">\r\n              <strong>(ii)<\/strong>&nbsp;&nbsp; Melting temperature depends on the strength of metallic bonding.<br>\r\n              Explain why the metallic bonding in magnesium is much stronger than that in sodium.\r\n            <\/div>\r\n\r\n            <div class=\"saq-student-box\">\r\n              <span id=\"saqStudentText\"><\/span><span id=\"saqStudentCursor\" class=\"cursor\"><\/span>\r\n            <\/div>\r\n          <\/section>\r\n\r\n          <section id=\"saqTeacherFeedback\" 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