{"id":4578,"date":"2026-05-30T06:12:27","date_gmt":"2026-05-30T05:12:27","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/ionic-bonding\/polarisation-of-ions\/"},"modified":"2026-10-25T12:06:51","modified_gmt":"2026-10-25T12:06:51","slug":"polarisation-of-ions","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/ionic-bonding\/polarisation-of-ions\/","title":{"rendered":"Polarisation of Ions"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-polarisation-of-ions-9ch0-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --soft-orange: #fff7ed;\n      --grey-text: #667085;\n      --body-text: #1f2937;\n      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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 2 Bonding and Structure<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/ionic-bonding\/\">Ionic Bonding<\/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-2-bonding-and-structure\/ionic-bonding\/nature-of-ionic-bonding\/\">Nature of Ionic Bonding<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/ionic-bonding\/polarisation-of-ions\/\">Polarisation of Ions<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/ionic-bonding\/physical-properties-of-ionic-compounds\/\">Physical Properties of Ionic Compounds<\/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-2-bonding-and-structure\/covalent-bonding\/\">Covalent Bonding<\/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-2-bonding-and-structure\/covalent-bonding\/nature-of-covalent-bonding\/\">Nature of Covalent Bonding<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/covalent-bonding\/dative-covalent-bonding\/\">Dative Covalent Bonding<\/a>\r\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/covalent-bonding\/giant-covalent-structures\/\">Giant Covalent Structures<\/a>\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/covalent-bonding\/electronegativity\/\">Electronegativity<\/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-2-bonding-and-structure\/shapes-of-molecules\/\">Shapes of Molecules<\/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-2-bonding-and-structure\/shapes-of-molecules\/linear\/\">Linear<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/trigonal-planar\/\">Trigonal Planar<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/tetrahedral\/\">Tetrahedral<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/trigonal-pyramidal\/\">Trigonal Pyramidal<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/bent\/\">Bent<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/trigonal-bipyramidal\/\">Trigonal Bipyramidal<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/octahedral\/\">Octahedral<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/square-planar\/\">Square Planar<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/square-pyramidal\/\">Square Pyramidal<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/distorted-t\/\">Distorted T<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/shapes-of-molecules\/seesaw\/\">SeeSaw<\/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-2-bonding-and-structure\/polar-molecules\/\">Polar Molecules<\/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-2-bonding-and-structure\/metallic-bonding\/\">Metallic Bonding<\/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-2-bonding-and-structure\/metallic-bonding\/metallic-bonding-and-structure\/\">Metallic Bonding and Structure<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/metallic-bonding\/physical-properties-of-metals\/\">Physical Properties of Metals<\/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-2-bonding-and-structure\/intermolecular-forces\/\">Intermolecular Forces<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/intermolecular-forces\/london-forces\/\">London Forces<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/intermolecular-forces\/permanent-dipole-dipole-forces\/\">Permanent Dipole-Dipole Forces<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/intermolecular-forces\/hydrogen-bonding\/\">Hydrogen Bonding<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/intermolecular-forces\/anomalous-properties-of-water\/\">Anomalous Properties of Water<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/intermolecular-forces\/boiling-temperature-trends\/\">Boiling Temperature Trends<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/intermolecular-forces\/choosing-solvents\/\">Choosing Solvents<\/a>\n          <\/li>\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-2-bonding-and-structure\/structure-types\/\">Structure Types<\/a>\r\n      <\/li>\r\n\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-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      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/\">Formulae, Equations &amp; Amounts<\/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      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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\/edexcel\/\">Edexcel<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/\">Topic 2 Bonding and Structure<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/ionic-bonding\/\">Ionic Bonding<\/a> \/\n        <span>Polarisation of Ions<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Polarisation of Ions<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to polarisation, polarising power, anion polarisability and covalent character for Edexcel A Level Chemistry.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Unit: Paper 1<\/div>\n          <div class=\"ols-badge\">Topic 2: Bonding and Structure<\/div>\n          <div class=\"ols-badge\">9CH0\/01<\/div>\n        <\/div>\n      <\/header>\n<!-- 3D card: anion-polarisation (swapped 26 Sep 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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text-align:center; font-size:11px; font-style:italic; color:#aab0c0;\n}\n.ols-cc-anpl-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-anpl-001 a:hover{text-decoration:underline;}\n.ols-anpl-001 .anpl-seg button{display:inline-flex; align-items:center;}\n.ols-anpl-001 .anpl-seg button .anpl-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-anpl-001 .anpl-seg button[aria-pressed=\"true\"] .anpl-n{background:#ffffff; color:#2563eb;}\n<\/style>\n\n<div class=\"anpl-head\">\n  <h2 class=\"anpl-title\">Polarisation of Anions by Cations<\/h2>\n  <p class=\"anpl-sub\">Choose a step to watch a small, highly charged cation pull an anion&#8217;s electron cloud out of shape, then change the anion, the cation and the covalent character.<\/p>\n<\/div>\n\n<div class=\"anpl-stage\" id=\"anplStage\">\n  <canvas class=\"anpl-canvas\" id=\"anplCanvas\"><\/canvas>\n  <div class=\"anpl-overlay\" id=\"anplOverlay\"><\/div>\n  <div class=\"anpl-caption\" id=\"anplCaption\"><\/div>\n  <div class=\"anpl-hint\" id=\"anplHint\">Drag to rotate<\/div>\n  <div class=\"anpl-badges\" id=\"anplBadges\"><\/div>\n<\/div>\n\n<div class=\"anpl-controls\">\n  <div class=\"anpl-row\">\n    <span class=\"anpl-rowlab\">Step<\/span>\n    <div class=\"anpl-seg\" role=\"group\" aria-label=\"Step\">\n      <button type=\"button\" data-step=\"1\" aria-pressed=\"true\"><span class=\"anpl-n\">1<\/span>Undistorted ions<\/button>\n      <button type=\"button\" data-step=\"2\" aria-pressed=\"false\"><span class=\"anpl-n\">2<\/span>The cation pulls<\/button>\n      <button type=\"button\" data-step=\"3\" aria-pressed=\"false\"><span class=\"anpl-n\">3<\/span>Change the anion<\/button>\n      <button type=\"button\" data-step=\"4\" aria-pressed=\"false\"><span class=\"anpl-n\">4<\/span>Change the cation<\/button>\n      <button type=\"button\" data-step=\"5\" aria-pressed=\"false\"><span class=\"anpl-n\">5<\/span>Covalent character<\/button>\n    <\/div>\n  <\/div>\n\n  <div class=\"anpl-row\">\n    <span class=\"anpl-rowlab\">View<\/span>\n    <button type=\"button\" class=\"anpl-pill\" id=\"anplResetV\">Reset view<\/button>\n  <\/div>\n<\/div>\n\n<div class=\"anpl-info\">\n  <h3 id=\"anplInfoTitle\"><\/h3>\n  <p id=\"anplInfoText\"><\/p>\n  <div class=\"anpl-facts\" id=\"anplFacts\"><\/div>\n  <div class=\"anpl-key\">\n    <span><i class=\"k-ball\" style=\"background:#b2b8c4\"><\/i>Al\u00b3\u207a or Mg\u00b2\u207a<\/span>\n    <span><i class=\"k-ball\" style=\"background:#8c52c4\"><\/i>Na\u207a<\/span>\n    <span><i class=\"\" style=\"background:rgba(52,170,72,0.55)\"><\/i>Cl\u207b electron cloud<\/span>\n    <span><i class=\"\" style=\"background:rgba(150,205,122,0.6)\"><\/i>F\u207b electron cloud<\/span>\n    <span><i class=\"\" style=\"background:rgba(104,40,120,0.5)\"><\/i>I\u207b electron cloud<\/span>\n    <span><i class=\"\" style=\"background:#ffffff;border-color:rgba(28,36,75,0.6)\"><\/i>Undistorted size<\/span>\n  <\/div>\n<\/div>\n\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/anion-polarisation.js?v=20261025p\"><\/script>\n<\/section>\n\n<p class=\"ols-cc-anpl-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\n\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: Ion Charges and Ionic or Covalent<\/h2>\n<p>Before you start, check the GCSE ideas about ions and bonding that this page builds on.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1294\"><\/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 Is Polarisation?<\/h2>\n        <\/div>\n\n        <p><strong>Polarisation<\/strong> occurs when a positive ion, called a <strong>cation<\/strong>, attracts and distorts the electron cloud of a negative ion, called an <strong>anion<\/strong>.<\/p>\n        <p>The anion is not pulled apart into separate particles. Instead, its electron cloud becomes unevenly distributed because the electrons are attracted towards the cation.<\/p>\n        <p>This distortion gives the bond more <strong>covalent character<\/strong>, because electron density is drawn between the two ions instead of being held as a completely separate spherical anion cloud.<\/p>\n\n        <div class=\"ols-definition-box\">\n          <p><strong>Definition:<\/strong> Polarising power is the ability of a cation to distort an anion. Polarisability is the ease with which an anion is distorted.<\/p>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> Polarisation explains why bonding is not always purely ionic or purely covalent. Many compounds lie on a bonding continuum between the two extremes.<\/p>\n        <\/div>\n\n        <div class=\"ols-zoom-card wide\">\n          <div class=\"ols-zoom-card-image\">\n            <img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/wave-50.jpg\" alt=\"Four-panel ionic to covalent continuum, NaCl to SiCl4, with the cation always navy and the anion always teal and the clouds merging more at each step\">\n          <\/div>\n          <div class=\"ols-zoom-card-caption\">\n            <p>Increasing polarisation changes the electron distribution between ions, so the bonding gains more covalent character.<\/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: Which Ion Is Distorted?<\/h2>\n<p>Decide which electron cloud is distorted in lithium iodide and why.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-601\" class=\"h5p-iframe\" data-content-id=\"601\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Polarisation MCQ: Which Electron Cloud Is Distorted in Lithium Iodide?\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">2<\/div>\n          <h2>Cation Polarising Power<\/h2>\n        <\/div>\n\n        <p>The ability of a cation to polarise an anion depends on its <strong>charge density<\/strong>. Charge density means charge relative to size.<\/p>\n        <p>A cation has greater polarising power when it has a <strong>higher positive charge<\/strong> or a <strong>smaller ionic radius<\/strong>. Both factors concentrate positive charge into a smaller volume.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Factor<\/th>\n                <th>Effect on polarising power<\/th>\n                <th>Example<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Factor\">Higher cation charge<\/td>\n                <td data-label=\"Effect on polarising power\">Increases attraction for the anion&#8217;s electrons, so the anion electron cloud is distorted more strongly.<\/td>\n                <td data-label=\"Example\">Mg<sup>2+<\/sup> has greater polarising power than Na<sup>+<\/sup> because Mg<sup>2+<\/sup> has a higher positive charge.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Factor\">Smaller cation radius<\/td>\n                <td data-label=\"Effect on polarising power\">Increases charge density because the positive charge is concentrated into a smaller volume.<\/td>\n                <td data-label=\"Example\">Li<sup>+<\/sup> has greater polarising power than Cs<sup>+<\/sup> because Li<sup>+<\/sup> is much smaller.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Factor\">Charge-to-radius ratio<\/td>\n                <td data-label=\"Effect on polarising power\">A cation with a larger charge-to-radius ratio has stronger polarising power.<\/td>\n                <td data-label=\"Example\">Ca<sup>2+<\/sup> has greater polarising power than Li<sup>+<\/sup> because its higher charge outweighs its larger size.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Typical polarising power order:<\/strong> Cs<sup>+<\/sup> &lt; Na<sup>+<\/sup> &lt; Li<sup>+<\/sup> &lt; Ca<sup>2+<\/sup> &lt; Mg<sup>2+<\/sup> &lt; Al<sup>3+<\/sup>.<\/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 More Polarising Cation<\/h2>\n<p>Click the more polarising cation in each pair.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-157\" class=\"h5p-iframe\" data-content-id=\"157\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Polarisation Mark the Words: The More Polarising Cation in Each Pair\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">3<\/div>\n          <h2>Anion Polarisability<\/h2>\n        <\/div>\n\n        <p>The ease with which an anion is polarised also depends on charge density. Anions are more easily polarised when their electron clouds are easier to distort.<\/p>\n        <p>A larger anion is more polarisable because its outer electrons are further from the nucleus and are held less strongly. An anion with a higher negative charge is also more polarisable because electron-electron repulsion is greater.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Factor<\/th>\n                <th>Effect on polarisability<\/th>\n                <th>Example<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Factor\">Higher negative charge<\/td>\n                <td data-label=\"Effect on polarisability\">Extra negative charge increases electron-electron repulsion, making the electron cloud easier to distort.<\/td>\n                <td data-label=\"Example\">O<sup>2-<\/sup> is more easily polarised than F<sup>&#8211;<\/sup>.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Factor\">Larger anion radius<\/td>\n                <td data-label=\"Effect on polarisability\">The outer electrons are further from the nucleus and are held less strongly.<\/td>\n                <td data-label=\"Example\">I<sup>&#8211;<\/sup> is more easily polarised than Cl<sup>&#8211;<\/sup> because I<sup>&#8211;<\/sup> is much larger.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Typical halide polarisability order:<\/strong> F<sup>&#8211;<\/sup> &lt; Cl<sup>&#8211;<\/sup> &lt; Br<sup>&#8211;<\/sup> &lt; I<sup>&#8211;<\/sup>.<\/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 Most Polarisable Anion<\/h2>\n<p>Choose the anion that is most easily polarised.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-158\" class=\"h5p-iframe\" data-content-id=\"158\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Polarisation MCQ: The Most Polarisable of Four Anions\"><\/iframe><\/div><\/div>\n<\/section>\n\n\n\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Polarisation and Covalent Character<\/h2>\n        <\/div>\n\n        <p>When polarisation is weak, the compound is closer to the ionic end of the bonding continuum. When polarisation is strong, the anion electron cloud is pulled towards the cation and the compound gains more covalent character.<\/p>\n        <p>Small, highly charged cations such as <strong>Al<sup>3+<\/sup><\/strong> and <strong>Si<sup>4+<\/sup><\/strong> can strongly distort the electron cloud of chloride ions. This is why aluminium chloride and silicon chloride bonding is more covalent than simple sodium chloride bonding.<\/p>\n\n        <div class=\"ols-rule-list\">\n          <div class=\"ols-rule-item\">\n            <h3>More ionic character<\/h3>\n            <p>Large or low-charge cations combined with small, low-polarisability anions tend to show more ionic character.<\/p>\n          <\/div>\n\n          <div class=\"ols-rule-item\">\n            <h3>More covalent character<\/h3>\n            <p>Small, highly charged cations combined with large, polarisable anions tend to show more covalent character.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-zoom-card wide\">\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-20.jpg\" alt=\"Aluminium halides from AlF\u2083 to AlI\u2083: the halide ion gets larger and more polarisable, so Al\u00b3\u207a distorts it more and covalent character increases.\"><\/div>\n<div class=\"ols-figure-caption\"><p>Bonding in aluminium halides showing increasing anion polarisation<\/p><\/div>\n<\/div>\n          <div class=\"ols-zoom-card-caption\">\n            <p>A highly charged Al<sup>3+<\/sup> ion distorts larger halide ions more strongly, increasing covalent character.<\/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: Rank the Covalent Character<\/h2>\n<p>Put the compounds in order from most ionic to most covalent character.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-159\" class=\"h5p-iframe\" data-content-id=\"159\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Polarisation Sort: Most Ionic to Most Covalent Character\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>How Polarisation Links to Ionic Bond Strength<\/h2>\n        <\/div>\n\n        <p>Ionic bond strength is affected by the electrostatic attraction between oppositely charged ions. Higher ionic charge and smaller ionic radius usually produce stronger attractions and higher melting temperatures.<\/p>\n        <p>Polarisation adds another layer of explanation. If the cation strongly distorts the anion, the bonding may gain covalent character instead of behaving like a simple ionic lattice.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Comparison<\/th>\n                <th>Main reason<\/th>\n                <th>Typical consequence<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Comparison\">NaF compared with CaO<\/td>\n                <td data-label=\"Main reason\">CaO contains Ca<sup>2+<\/sup> and O<sup>2-<\/sup>, so the ionic charges are larger.<\/td>\n                <td data-label=\"Typical consequence\">Stronger electrostatic attraction and a much higher melting temperature.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Comparison\">NaF compared with CsF<\/td>\n                <td data-label=\"Main reason\">Na<sup>+<\/sup> is smaller than Cs<sup>+<\/sup>, so Na<sup>+<\/sup> and F<sup>&#8211;<\/sup> ions can sit closer together.<\/td>\n                <td data-label=\"Typical consequence\">Stronger electrostatic attraction in NaF than in CsF.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Comparison\">NaCl compared with AlCl<sub>3<\/sub><\/td>\n                <td data-label=\"Main reason\">Al<sup>3+<\/sup> is small and highly charged, so it strongly polarises Cl<sup>&#8211;<\/sup>.<\/td>\n                <td data-label=\"Typical consequence\">AlCl<sub>3<\/sub> shows greater covalent character than NaCl.<\/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: Explain a Group 2 Contrast<\/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-602\" class=\"h5p-iframe\" data-content-id=\"602\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Polarisation Explain: Beryllium Chloride Compared with Barium Chloride\"><\/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: Which Reason Applies?<\/h2>\n<p>In each round, choose the statement with the correct comparison and the correct reason.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-156\" class=\"h5p-iframe\" data-content-id=\"156\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Polarisation Summary: Charge, Radius or Polarisation?\"><\/iframe><\/div><\/div>\n<\/section>\n\n      \n\n      <section class=\"ols-faq-card ols-quicksnap-card\">\n        <h2>QuickSnap<\/h2>\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>1. Polarisation<\/h3>\n            <p>Polarisation is the distortion of an anion&#8217;s electron cloud by a nearby cation. The more the electron cloud is distorted, the more covalent character the bonding can show.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>2. Cation polarising power<\/h3>\n            <p>Small, highly charged cations have high charge density and strong polarising power. Al<sup>3+<\/sup> is strongly polarising because it is small and has a 3+ charge.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>3. Anion polarisability<\/h3>\n            <p>Large anions and anions with higher negative charge are more easily polarised because their outer electron clouds are held less strongly.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>4. Aluminium halide comparison<\/h3>\n            <p>F<sup>&#8211;<\/sup> is small and difficult to polarise, so AlF<sub>3<\/sub> is more ionic. Cl<sup>&#8211;<\/sup> is larger and more polarisable, so AlCl<sub>3<\/sub> shows greater covalent character.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>5. Exam link<\/h3>\n            <p>When explaining covalent character in ionic compounds, link cation charge density to anion distortion, then link the distortion to increased sharing of electron density.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <!-- author card (moved to the end, 10 Oct 2026) -->\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\n        class=\"ols-linkedin-pill\"\n        href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\"\n        target=\"_blank\"\n        rel=\"noopener noreferrer\"\n      >\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\n\n      <section class=\"ols-faq-card\">\n        <h2>Frequently Asked Questions<\/h2>\n        <p>Use these quick answers to check the key language needed for polarisation of ions questions.<\/p>\n\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>What is polarisation in ionic bonding?<\/h3>\n            <p>Polarisation is the distortion of an anion&#8217;s electron cloud by a nearby cation. This can make the bonding show greater covalent character.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What increases the polarising power of a cation?<\/h3>\n            <p>A cation has greater polarising power when it has a higher positive charge and a smaller ionic radius. Both increase charge density.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What makes an anion more polarisable?<\/h3>\n            <p>An anion is more polarisable when it is larger or has a higher negative charge. Larger anions have outer electrons further from the nucleus, so their electron clouds are easier to distort.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why does Al<sup>3+<\/sup> have strong polarising power?<\/h3>\n            <p>Al<sup>3+<\/sup> has a high positive charge and a small ionic radius, giving it a high charge density. This allows it to strongly attract and distort anion electron clouds.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>How does polarisation affect bonding?<\/h3>\n            <p>Greater polarisation increases covalent character because electron density is pulled towards the cation and becomes shared to a greater extent between the ions.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-related-card\">\n        <h2>Related Revision Notes<\/h2>\n        <p>Continue building Topic 2 Bonding and Structure by linking polarisation to ionic bonding, covalent bonding and metallic bonding.<\/p>\n\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/ionic-bonding\/nature-of-ionic-bonding\/\">Nature of Ionic Bonding<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/ionic-bonding\/physical-properties-of-ionic-compounds\/\">Physical Properties of Ionic Compounds<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/covalent-bonding\/\">Covalent Bonding<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/covalent-bonding\/electronegativity\/\">Electronegativity<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/metallic-bonding\/metallic-bonding-and-structure\/\">Metallic Bonding and 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\/\">Topic 2 Bonding and 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\" aria-hidden=\"true\" role=\"dialog\" aria-label=\"Image lightbox\">\n        <div class=\"ols-image-lightbox-inner\">\n          <button class=\"ols-image-lightbox-close\" type=\"button\" aria-label=\"Close image\">&times;<\/button>\n          <img decoding=\"async\" class=\"ols-image-lightbox-img\" src=\"\" alt=\"\">\n        <\/div>\n      <\/div>\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-2-bonding-and-structure\/ionic-bonding\/polarisation-of-ions\/#webpage\",\n            \"url\": 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Unit: Paper 1 Topic 2: Bonding and Structure 9CH0\/01 Polarisation of Anions by [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":0,"parent":4570,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-4578","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4578","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=4578"}],"version-history":[{"count":2,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4578\/revisions"}],"predecessor-version":[{"id":24418,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4578\/revisions\/24418"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/4570"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=4578"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}