{"id":8135,"date":"2026-09-16T17:24:17","date_gmt":"2026-09-16T16:24:17","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/permanent-dipole-dipole-forces\/"},"modified":"2026-10-23T21:43:48","modified_gmt":"2026-10-23T20:43:48","slug":"permanent-dipole-dipole-forces","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/permanent-dipole-dipole-forces\/","title":{"rendered":"Permanent Dipole-Dipole Forces"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-imf-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      --gold: #c9973a;\n      --grey-text: #667085;\n      --body-text: #1f2937;\n    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14px;\n      line-height: 1.65;\n      font-weight: 300;\n      color: #667085;\n    }\n    .ols-attribution-card strong { font-weight: 700; color: #1C244B; }\n      .ols-note-card h3 { margin: 22px 0 8px; font-size: 18px; line-height: 1.25; font-weight: 500; color: var(--navy); }\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>A Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Topic 7 Intermolecular Forces<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/\">Topic 7 Overview<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-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-international\/topic-7-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-international\/topic-7-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-international\/topic-7-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-international\/topic-7-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-international\/topic-7-intermolecular-forces\/choosing-solvents\/\">Choosing Solvents<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Other Topics<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-3-bonding-structure\/\">Bonding &amp; Structure<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-5-alkenes\/\">Alkenes<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-6-energetics\/\">Energetics<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8A-redox-chemistry\/\">Redox Chemistry<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\n\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      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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-international\/\">Edexcel International<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/\">Topic 7 Intermolecular Forces<\/a> \/\n<span>Permanent Dipole-Dipole Forces<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Permanent Dipole-Dipole Forces<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to permanent dipole-permanent dipole interactions: which molecules have a permanent dipole, how polar molecules attract each other, why the attraction adds to London forces, and how to decide the forces in an unfamiliar molecule, for Edexcel International A Level Chemistry.<\/p>\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Exam board: Edexcel International<\/div>\n<div class=\"ols-badge\">Unit 2: WCH12\/01<\/div>\n<div class=\"ols-badge\">Topic 7: Intermolecular Forces<\/div>\n<\/div>\n      <\/header>\n<!-- 3D card: dipole-dipole-attraction (23 Oct 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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border-radius:22px;}\n  .ols-dpd-001 h2.dpd-title{font-size:20.5px;}\n  .ols-dpd-001 p.dpd-sub{font-size:13.5px;}\n  .ols-dpd-001 .dpd-stage{height:400px;}\n  .ols-dpd-001 .dpd-rowlab{min-width:100%;}\n  .ols-dpd-001 .dpd-seg button{padding:9px 13px; font-size:13px;}\n  .ols-dpd-001 .dpd-lab{font-size:10.5px; padding:4px 8px;}\n  .ols-dpd-001 .dpd-lab.l-part{font-size:9.5px; padding:3px 7px;}\n  .ols-dpd-001 .dpd-lab.l-read{font-size:12px; padding:5px 9px;}\n  .ols-dpd-001 .dpd-caption{font-size:10.5px; padding:5px 9px; max-width:64%;}\n  .ols-dpd-001 .dpd-badge{font-size:10.5px; padding:4px 9px;}\n  .ols-dpd-001 .dpd-badge.b-eq{font-size:11px;}\n  .ols-dpd-001 .dpd-badges{max-width:calc(100% - 28px);}\n  .ols-dpd-001 .dpd-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-dpd-001 .dpd-hint{display:none;}\n  .ols-dpd-001 .dpd-caption{max-width:calc(100% - 28px);}\n}\n@media (prefers-reduced-motion:reduce){\n  .ols-dpd-001 .dpd-seg button,.ols-dpd-001 .dpd-pill{transition:none;}\n}\n\n.ols-cc-dpd-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-dpd-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-dpd-001 a:hover{text-decoration:underline;}\n.ols-dpd-001 .dpd-seg button{display:inline-flex; align-items:center;}\n.ols-dpd-001 .dpd-seg button .dpd-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-dpd-001 .dpd-seg button[aria-pressed=\"true\"] .dpd-n{background:#ffffff; color:#2563eb;}\n<\/style>\n\n<div class=\"dpd-head\">\n  <h2 class=\"dpd-title\">Permanent Dipole-Dipole Forces<\/h2>\n  <p class=\"dpd-sub\">Choose a step to see why the H\u2013Cl bond is polar, how neighbouring HCl molecules attract, how they line up in the liquid, and why a molecule with polar bonds can still have no permanent dipole.<\/p>\n<\/div>\n\n<div class=\"dpd-stage\" id=\"dpdStage\">\n  <canvas class=\"dpd-canvas\" id=\"dpdCanvas\"><\/canvas>\n  <div class=\"dpd-overlay\" id=\"dpdOverlay\"><\/div>\n  <div class=\"dpd-caption\" id=\"dpdCaption\"><\/div>\n  <div class=\"dpd-hint\" id=\"dpdHint\">Drag to rotate<\/div>\n  <div class=\"dpd-badges\" id=\"dpdBadges\"><\/div>\n<\/div>\n\n<div class=\"dpd-controls\">\n  <div class=\"dpd-row\">\n    <span class=\"dpd-rowlab\">Step<\/span>\n    <div class=\"dpd-seg\" role=\"group\" aria-label=\"Step\">\n      <button type=\"button\" data-step=\"1\" aria-pressed=\"true\"><span class=\"dpd-n\">1<\/span>A permanent dipole<\/button>\n      <button type=\"button\" data-step=\"2\" aria-pressed=\"false\"><span class=\"dpd-n\">2<\/span>Attraction<\/button>\n      <button type=\"button\" data-step=\"3\" aria-pressed=\"false\"><span class=\"dpd-n\">3<\/span>In a liquid<\/button>\n      <button type=\"button\" data-step=\"4\" aria-pressed=\"false\"><span class=\"dpd-n\">4<\/span>Polar or not?<\/button>\n    <\/div>\n  <\/div>\n\n  <div class=\"dpd-row\">\n    <span class=\"dpd-rowlab\">View<\/span>\n    <button type=\"button\" class=\"dpd-pill\" id=\"dpdResetV\">Reset view<\/button>\n  <\/div>\n<\/div>\n\n<div class=\"dpd-info\">\n  <h3 id=\"dpdInfoTitle\"><\/h3>\n  <p id=\"dpdInfoText\"><\/p>\n  <div class=\"dpd-facts\" id=\"dpdFacts\"><\/div>\n  <div class=\"dpd-key\">\n    <span><i class=\"k-ball\" style=\"background:#ececf0\"><\/i>Hydrogen<\/span>\n    <span><i class=\"k-ball\" style=\"background:#34aa48\"><\/i>Chlorine<\/span>\n    <span><i class=\"k-ball\" style=\"background:#96d75a\"><\/i>Fluorine<\/span>\n    <span><i class=\"k-ball\" style=\"background:#464a54\"><\/i>Carbon<\/span>\n    <span><i class=\"k-ball\" style=\"background:#cd2d28\"><\/i>Oxygen<\/span>\n    <span><i class=\"k-ball\" style=\"background:#f6c426\"><\/i>Bonding pair<\/span>\n    <span><i class=\"\" style=\"background:#ffffff;border-color:rgba(37,99,235,0.9);border-style:dashed\"><\/i>Dipole-dipole force<\/span>\n    <span><i class=\"\" style=\"background:#ffffff;border-color:rgba(28,36,75,0.4);border-style:dashed\"><\/i>London force<\/span>\n  <\/div>\n<\/div>\n\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/dipole-dipole-attraction.js?v=20261023d\"><\/script>\n<\/section>\n\n<p class=\"ols-cc-dpd-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: Shared Pairs and Simple Molecules<\/h2>\n<p>Four quick GCSE questions on covalent bonds and molecules before you meet polar molecules.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"1323\"><\/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>Polar Molecules and Permanent Dipoles<\/h2>\n<\/div>\n<p>A <strong>permanent dipole<\/strong> exists in a molecule that contains polar bonds whose dipoles do not cancel, so one end of the molecule is always \u03b4+ and the other always \u03b4-. Permanent dipole-permanent dipole interactions are the attractions between the \u03b4+ end of one such molecule and the \u03b4- end of a neighbour.<\/p>\n<p>Two conditions must both hold. First, the molecule must contain a bond between atoms of different electronegativity, such as H-Cl, C-Cl, C-F or C=O. Second, the shape of the molecule must leave an overall dipole.<\/p><p>CO\u2082 has two very polar C=O bonds, but the molecule is linear and the two bond dipoles cancel. So CO\u2082 has no permanent dipole and only London forces act between its molecules.<\/p><p>The same applies to CCl\u2084 and BF\u2083.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Molecule<\/th><th>Polar bonds?<\/th><th>Shape<\/th><th>Overall dipole?<\/th><th>Strongest intermolecular force<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>HCl<\/strong><\/td><td>yes<\/td><td>linear, two atoms<\/td><td>yes<\/td><td>permanent dipole-permanent dipole interactions<\/td><\/tr>\n<tr><td><strong>CH\u2083Cl<\/strong><\/td><td>yes<\/td><td>tetrahedral, one Cl<\/td><td>yes<\/td><td>permanent dipole-permanent dipole interactions<\/td><\/tr>\n<tr><td><strong>CO\u2082<\/strong><\/td><td>yes<\/td><td>linear, symmetric<\/td><td>no<\/td><td>London forces<\/td><\/tr>\n<tr><td><strong>CCl\u2084<\/strong><\/td><td>yes<\/td><td>tetrahedral, symmetric<\/td><td>no<\/td><td>London forces<\/td><\/tr>\n<tr><td><strong>SO\u2082<\/strong><\/td><td>yes<\/td><td>bent<\/td><td>yes<\/td><td>permanent dipole-permanent dipole interactions<\/td><\/tr>\n<tr><td><strong>N\u2082<\/strong><\/td><td>no<\/td><td>linear<\/td><td>no<\/td><td>London forces<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Polar bonds are necessary but not sufficient. Ask whether the bond dipoles cancel in three dimensions before deciding that a molecule is polar.<\/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 the Bond Dipoles Cancel?<\/h2>\n<p>Four molecules, four shapes, one overall dipole. Draw them before you choose.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-527\" class=\"h5p-iframe\" data-content-id=\"527\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Permanent Dipoles MCQ: Which of These Four Molecules Is Polar\"><\/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>How the Molecules Line Up<\/h2>\n<\/div>\n<p>In a liquid such as hydrogen chloride the molecules tumble constantly. On average, though, they spend more time with their \u03b4+ hydrogen close to the \u03b4- chlorine of a neighbour than in any other arrangement.<\/p><p>This partial alignment produces a net attraction that is stronger than London forces alone for molecules of similar size, so more energy is needed to pull the molecules apart.<\/p>\n<div class=\"ols-figure-card ols-zoom-pop\">\n<div class=\"ols-figure-image\">\n<a class=\"ols-image-fullscreen-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/intermolecular-forces-in-hydrogen-chloride-and-fluorine.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/intermolecular-forces-in-hydrogen-chloride-and-fluorine.jpg\" alt=\"Polar hydrogen chloride molecules aligned by permanent dipole-dipole attractions, beside non-polar fluorine molecules held only by London forces\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/intermolecular-forces-in-hydrogen-chloride-and-fluorine.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Polar molecules attract each other by the alignment of their permanent dipoles; this attraction acts in addition to the London forces that every molecule has.<\/p><\/div>\n<\/div>\n<p>The alignment is never perfect, because thermal motion keeps disturbing it, which is why permanent dipole-permanent dipole interactions are still weak compared with covalent bonds and why polar liquids such as HCl still boil far below room temperature.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Remember:<\/strong> Permanent dipole-permanent dipole interactions act <strong>in addition to<\/strong> London forces, never instead of them.<\/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: Lined Up or Tumbling?<\/h2>\n<p>Judge one statement about what polar molecules are actually doing in a liquid.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-786\" class=\"h5p-iframe\" data-content-id=\"786\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Permanent Dipoles True or False: How Polar Molecules Sit in a Liquid\"><\/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>Comparing Molecules With Similar Numbers of Electrons<\/h2>\n<\/div>\n<p>The fair way to show that a permanent dipole raises the boiling temperature is to compare two molecules with the same number of electrons, so that their London forces are similar.<\/p><p>Hydrogen chloride and fluorine both have 18 electrons. F\u2082 is non-polar and boils at -188 \u00b0C; HCl is polar and boils at -85 \u00b0C.<\/p><div class=\"ols-key-box\"><p><strong>Key idea:<\/strong> The extra 100 \u00b0C comes from the permanent dipole-permanent dipole interactions.<\/p><\/div>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Pair<\/th><th>Electrons<\/th><th>Polar?<\/th><th>boiling temperature \/ \u00b0C<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>F\u2082<\/strong><\/td><td>18<\/td><td>no<\/td><td>-188<\/td><\/tr>\n<tr><td><strong>HCl<\/strong><\/td><td>18<\/td><td>yes<\/td><td>-85<\/td><\/tr>\n<tr><td><strong>Butane, C\u2084H\u2081\u2080<\/strong><\/td><td>34<\/td><td>no<\/td><td>-1<\/td><\/tr>\n<tr><td><strong>Propanone, CH\u2083COCH\u2083<\/strong><\/td><td>32<\/td><td>yes (C=O)<\/td><td>56<\/td><\/tr>\n<tr><td><strong>Ethane, C\u2082H\u2086<\/strong><\/td><td>18<\/td><td>no<\/td><td>-89<\/td><\/tr>\n<tr><td><strong>Fluoromethane, CH\u2083F<\/strong><\/td><td>18<\/td><td>yes (C-F)<\/td><td>-78<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Propanone and butane make the same point with organic molecules: almost the same electron count, but the C=O dipole in propanone lifts its boiling temperature by nearly 60 \u00b0C.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Propanone has a higher boiling temperature than butane because propanone molecules have a permanent dipole, so permanent dipole-permanent dipole interactions act between them in addition to London forces, and more energy is needed to separate the molecules.<\/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: A Fair Comparison of Two Small Molecules<\/h2>\n<p>Build the comparison between two molecules of almost equal electron count with a 124 \u00b0C gap in boiling temperature.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-526\" class=\"h5p-iframe\" data-content-id=\"526\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Permanent Dipoles Drag: Propane Against Ethanenitrile\"><\/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 a Boiling Temperature<\/h2>\n<p>Write a short explanation for two isomers that differ only in where their chlorine atoms sit.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-528\" class=\"h5p-iframe\" data-content-id=\"528\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Permanent Dipoles Explain: The Two Isomers of 1,2-Dichloroethene\"><\/iframe><\/div><\/div>\n<\/section>\n\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Deciding the Forces in an Unfamiliar Molecule<\/h2>\n<\/div>\n<p>Exam questions often give a molecule you have never met and ask which intermolecular forces act between its molecules. Use three questions in order.<\/p>\n<ol>\n<li><strong>Does the molecule contain an H atom bonded directly to N, O or F?<\/strong> If yes, hydrogen bonding is present (see the <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/hydrogen-bonding\/\">Hydrogen Bonding<\/a> page), and so are the two forces below.<\/li>\n<li><strong>Does the molecule have an overall permanent dipole?<\/strong> Check for polar bonds and then check that the shape does not cancel them. If yes, permanent dipole-permanent dipole interactions are present, plus London forces.<\/li>\n<li><strong>Every molecule<\/strong> has London forces. If the answers to questions 1 and 2 are no, these are the only forces.<\/li>\n<\/ol>\n<p>For example, chloromethane, CH\u2083Cl, has no H bonded to N, O or F. It has a polar C-Cl bond in a tetrahedral molecule with only one chlorine, so it has an overall dipole: permanent dipole-permanent dipole interactions plus London forces.<\/p><p>Methanal, HCHO, has a C=O dipole: the same answer.<\/p><p>Tetrachloromethane, CCl\u2084, has four polar bonds that cancel: London forces only.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Name every force that is present and say which is the strongest. A list with one force missing loses the mark even if the strongest is right.<\/p>\n<\/div>\n<div class=\"ols-figure-card ols-zoom-pop\">\n<div class=\"ols-figure-image\">\n<a class=\"ols-image-fullscreen-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/t17x-s3forcestree.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/t17x-s3forcestree.jpg\" alt=\"Decision tree for intermolecular forces with worked results for chloromethane, methanal, tetrachloromethane and water.\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/t17x-s3forcestree.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Ask whether there is an H on N, O or F, then whether there is an overall dipole, and remember that every molecule also has London forces.<\/p><\/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: Name Every Force<\/h2>\n<p>Run the three questions in order over five molecules you have not met on this page.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-529\" class=\"h5p-iframe\" data-content-id=\"529\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Permanent Dipoles Rapid Check: Naming the Forces in Five New Molecules\"><\/iframe><\/div><\/div>\n<\/section>\n\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Permanent Dipoles and Solubility<\/h2>\n<\/div>\n<p>Polar molecules tend to dissolve in polar solvents and non-polar molecules in non-polar solvents. A solute dissolves when the new attractions it makes with solvent molecules are similar in strength to the attractions it loses.<\/p>\n<p>Propanone mixes with water in all proportions because its C=O oxygen can accept a hydrogen bond from water.<\/p>\n<p>Hexane does not mix with water because the only forces hexane can offer are London forces. The <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/choosing-solvents\/\">Choosing Solvents<\/a> page develops this idea.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Like dissolves like: match the strongest intermolecular force in the solute to the strongest force in the solvent.<\/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 Ideas That Catch People Out<\/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-787\" class=\"h5p-iframe\" data-content-id=\"787\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Permanent Dipoles Summary: Shape, Tumbling and Fair Comparisons\"><\/iframe><\/div><\/div>\n<\/section>\n\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Common Exam Points<\/h2>\n<\/div>\n<h3>Explain why HCl boils higher than F\u2082<\/h3><p>Similar electrons, so similar London forces; HCl is polar, so permanent dipole-permanent dipole interactions act as well; more energy is needed to separate HCl molecules.<\/p>\n<h3>Explain why CO\u2082 is non-polar although C=O bonds are polar<\/h3><p>The molecule is linear and symmetrical, so the two bond dipoles cancel and there is no overall dipole.<\/p>\n<h3>State the intermolecular forces in CH\u2083Br<\/h3><p>Permanent dipole-permanent dipole interactions and London forces; no hydrogen bonding because no H is bonded to N, O or F.<\/p>\n<h3>Do not say<\/h3><p>&#8220;Polar molecules have no London forces&#8221;; &#8220;any molecule with a polar bond is polar&#8221;.<\/p>\n<\/article>\n\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Use these quick answers to check how Edexcel International expects permanent dipoles to be identified and explained.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>What is a permanent dipole?<\/h3>\n<p>It is a separation of charge that is always present in a molecule, because the molecule contains polar bonds whose dipoles do not cancel. One end of the molecule is permanently \u03b4+ and the other permanently \u03b4-.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Does a polar bond always make a polar molecule?<\/h3>\n<p>No. CO\u2082 and CCl\u2084 both contain very polar bonds, but the molecules are symmetrical, so the bond dipoles cancel and there is no overall dipole. Always check the shape before deciding.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How do I decide which forces act between molecules of an unfamiliar substance?<\/h3>\n<p>Ask three questions in order: is a hydrogen atom bonded directly to N, O or F (hydrogen bonding); does the molecule have an overall permanent dipole (permanent dipole-permanent dipole interactions); and finally, every molecule has London forces.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Which is stronger, a permanent dipole attraction or London forces?<\/h3>\n<p>For molecules of a similar size, the permanent dipole-permanent dipole attraction is stronger. For a much larger molecule the London forces can be bigger in total, which is why HI boils higher than HCl even though HCl is more polar.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How should I show this in an answer?<\/h3>\n<p>Compare molecules with a similar number of electrons so the London forces are similar, then attribute the difference to the permanent dipole and finish with the energy statement.<\/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        <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        View LinkedIn Profile\n      <\/a>\n\n    <\/div>\n\n  <\/div>\n\n<section class=\"ols-related-card\">\n<h2>Related Topic 7 Pages<\/h2>\n<p>Use these pages to connect the three intermolecular forces with the physical properties they explain.<\/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-international\/topic-7-intermolecular-forces\/london-forces\/\">London Forces<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/hydrogen-bonding\/\">Hydrogen Bonding<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/anomalous-properties-of-water\/\">Anomalous Properties of Water<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/boiling-temperature-trends\/\">Boiling Temperature Trends<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/choosing-solvents\/\">Choosing Solvents<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-3-bonding-structure\/polar-and-non-polar-molecules\/\">Polar &amp; Non-Polar Molecules<\/a>\n<\/div>\n<\/section>\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    <\/main>\n  \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-international\/topic-7-intermolecular-forces\/permanent-dipole-dipole-forces\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-7-intermolecular-forces\/permanent-dipole-dipole-forces\/\",\n      \"name\": \"Permanent Dipole-Dipole Forces | Topic 7 Intermolecular Forces | Online Learning System\",\n      \"description\": \"Permanent dipole-permanent dipole interactions for Edexcel International A Level Chemistry: polar molecules, bond dipoles that cancel, comparing molecules with similar electrons and a routine for unfamiliar 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