{"id":8157,"date":"2026-09-16T17:33:30","date_gmt":"2026-09-16T16:33:30","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/anomalous-properties-of-water\/"},"modified":"2026-09-18T11:29:59","modified_gmt":"2026-09-18T10:29:59","slug":"anomalous-properties-of-water","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/anomalous-properties-of-water\/","title":{"rendered":"Anomalous Properties of Water"},"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-nature-of-covalent-bonding-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      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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\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>AQA A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>3.1.3 Bonding<\/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\/aqa\/3-1-3-bonding\/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\/aqa\/3-1-3-bonding\/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\/aqa\/3-1-3-bonding\/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\/aqa\/3-1-3-bonding\/ionic-bonding\/physical-properties-of-ionic-compounds\/\">Physical Properties of Ionic Compounds<\/a>\r\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/ionic-bonding\/ions-and-ionic-formulae\/\">Ions and Ionic Formulae<\/a>\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\/aqa\/3-1-3-bonding\/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\/aqa\/3-1-3-bonding\/covalent-bonding\/covalent-bonding\/\">Covalent Bonding<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/covalent-bonding\/dative-covalent-bonding\/\">Dative Covalent Bonding<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/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\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/\">Shapes of Molecules and Ions<\/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\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/linear\/\">Linear<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/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\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/tetrahedral\/\">Tetrahedral<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/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\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/bent\/\">Bent<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/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\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/octahedral\/\">Octahedral<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/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\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/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\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/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\/aqa\/3-1-3-bonding\/shapes-of-molecules-and-ions\/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\/aqa\/3-1-3-bonding\/bond-polarity\/\">Bond Polarity<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/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\/aqa\/3-1-3-bonding\/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\/aqa\/3-1-3-bonding\/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\/aqa\/3-1-3-bonding\/giant-covalent-structures\/\">Giant Covalent Structures<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/simple-molecular-structures\/\">Simple Molecular Structures<\/a>\r\n      <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/structure-types\/\">Structure Types<\/a>\n          <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/\">Intermolecular Forces<\/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\/aqa\/3-1-3-bonding\/intermolecular-forces\/london-forces\/\">London Forces<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/permanent-dipole-dipole-forces\/\">Permanent Dipole-Dipole Forces<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/hydrogen-bonding\/\">Hydrogen Bonding<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/anomalous-properties-of-water\/\">Anomalous Properties of Water<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/boiling-temperature-trends\/\">Boiling Point Trends<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/choosing-solvents\/\">Choosing Solvents<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Adjacent 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\/aqa\/3-1-1-atomicstructure\/\">3.1.1 Atomic Structure<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-2-amount-of-substance\/\">3.1.2 Amount of Substance<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-4-energetics\/\">3.1.4 Energetics<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-2-1-periodicity\/\">3.2.1 Periodicity<\/a>\r\n      <\/li>\r\n    <\/ul>\r\n  <\/div>\r\n<\/aside>\r\n\r\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n    var matched = null;\r\n    var matchedLength = 0;\r\n\r\n    sidebar.querySelectorAll('.active, .active-main, .parent-active').forEach(function(item) {\r\n      item.classList.remove('active', 'active-main', 'parent-active');\r\n    });\r\n\r\n    sidebar.querySelectorAll('a[data-ols-disabled-parent=\"1\"], 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true;\r\n  }\r\n\r\n  if (!highlightActive()) {\r\n    document.addEventListener('DOMContentLoaded', highlightActive);\r\n  }\r\n})();\r\n<\/script>\n\n  <main class=\"ols-main\">\n      <nav class=\"ols-breadcrumbs\" aria-label=\"Breadcrumb\">\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\">Revision Notes<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\">A Level Chemistry<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/\">AQA<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/\">3.1.3 Bonding<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/\">Intermolecular Forces<\/a> \/\n<span>Anomalous Properties of Water<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Anomalous Properties of Water<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to the anomalous properties of water: its high melting point and boiling point, the open structure and low density of ice, surface tension and the Group 4 to 7 hydride graph, all explained by hydrogen bonding, for AQA A Level Chemistry.<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Paper 1 and 2 AQA<\/div>\n<div class=\"ols-badge\">3.1.3 Bonding<\/div>\n<div class=\"ols-badge\">7405\/1 and 7405\/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:<br><span>Dr. Mohammed Al-Fatah<\/span>\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        <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      <\/header>\n\n      <article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>Why Water Is Anomalous<\/h2>\n<\/div>\n<p>Water has a much higher melting point and boiling point, a solid that is less dense than its liquid, and a higher surface tension than any molecule of its size should have. Every one of these <strong>anomalous properties<\/strong> is caused by <strong>hydrogen bonding<\/strong>. A molecule with only 10 electrons would be expected to boil below -80 \u00b0C if induced dipole-dipole forces were the only force present; water boils at 100 \u00b0C.<\/p>\n<p>Each water molecule can form up to four hydrogen bonds, more than any other small molecule, so a very large amount of energy is needed to separate the molecules. This is the single explanation behind all the anomalies on this page.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Two O-H bonds and two lone pairs per molecule mean water forms the maximum number of hydrogen bonds, and every anomalous property follows from that.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>High Melting point and Boiling point<\/h2>\n<\/div>\n<p>The hydrides of Group 6 show the effect most clearly. Going down the group from H\u2082S to H\u2082Te the boiling point rises steadily because the number of electrons rises and the induced dipole-dipole forces strengthen. Extending that trend upwards predicts a boiling point for water of about -80 \u00b0C. The real value is 100 \u00b0C, because hydrogen bonds between water molecules are far stronger than the induced dipole-dipole forces and permanent dipole-dipole forces that hold the other hydrides together.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Hydride<\/th><th>Electrons<\/th><th>boiling point \/ \u00b0C<\/th><th>Strongest intermolecular force<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>H\u2082O<\/strong><\/td><td>10<\/td><td>100<\/td><td>hydrogen bonds<\/td><\/tr>\n<tr><td><strong>H\u2082S<\/strong><\/td><td>18<\/td><td>-60<\/td><td>permanent dipole-dipole forces<\/td><\/tr>\n<tr><td><strong>H\u2082Se<\/strong><\/td><td>36<\/td><td>-41<\/td><td>permanent dipole-dipole forces (induced dipole-dipole forces growing)<\/td><\/tr>\n<tr><td><strong>H\u2082Te<\/strong><\/td><td>54<\/td><td>-2<\/td><td>induced dipole-dipole forces dominate<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/boiling-temperatures-of-group-4-7-hydrides-hydrogen-bonding-anomalies.jpg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/boiling-temperatures-of-group-4-7-hydrides-hydrogen-bonding-anomalies.jpg\" alt=\"Boiling points of the Group 4 to 7 hydrides, with water, ammonia and hydrogen fluoride standing far above the trend because of hydrogen bonding\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>NH\u2083, H\u2082O and HF sit far above the trend of their groups because of hydrogen bonding; CH\u2084 does not, because carbon is not electronegative enough for C-H to hydrogen bond.<\/p><\/div>\n<\/div>\n<p>The same graph shows that methane is not anomalous: carbon is not electronegative enough for a C-H hydrogen to form a hydrogen bond, so the Group 4 hydrides follow a smooth induced dipole-dipole forces trend. Ammonia and hydrogen fluoride are anomalous but less so than water, because each forms on average only one hydrogen bond per molecule.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Water has a much higher boiling point than H\u2082S because water molecules form hydrogen bonds, which are much stronger than the permanent dipole-dipole forces and induced dipole-dipole forces between H\u2082S molecules, so much more energy is needed to separate water molecules.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>The Density of Ice<\/h2>\n<\/div>\n<p>Ice floats on water because it is <strong>less dense<\/strong>: 0.92 g cm\u207b\u00b3 against 1.00 g cm\u207b\u00b3 for water at 4 \u00b0C. Almost every other substance is denser as a solid than as a liquid, because the particles pack more closely when they stop moving. Water is different because of the geometry of its hydrogen bonds.<\/p>\n<p>In ice each water molecule is held by four hydrogen bonds to four neighbours arranged tetrahedrally around it, and the hydrogen bonds are fixed in place. This tetrahedral arrangement builds an <strong>open hexagonal lattice<\/strong> with large empty spaces, like a honeycomb, so the molecules are held further apart than they would be if they could pack freely. When ice melts, some of the hydrogen bonds break and the molecules can move into the spaces, so the liquid is denser than the solid. Water reaches its maximum density at 4 \u00b0C; above that, thermal expansion takes over.<\/p>\n<section class=\"ols-ice-001\" id=\"olsIce001\">\n<style>\n@import url('https:\/\/fonts.googleapis.com\/css2?family=Poppins:wght@300;400;500;600&display=swap');\n\n.ols-ice-001{\n  font-family:'Poppins',system-ui,-apple-system,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;\n  color:#1C244B; background:#ffffff;\n  border:1px solid rgba(28,36,75,0.14);\n  border-radius:28px;\n  box-shadow:0 18px 45px rgba(28,36,75,0.10);\n  padding:44px; margin:26px auto; max-width:980px;\n  box-sizing:border-box; -webkit-font-smoothing:antialiased;\n}\n.ols-ice-001 *{box-sizing:border-box;}\n\n.ols-ice-001 .ice-head{margin:0 0 22px;}\n.ols-ice-001 h2.ice-title{\n  font-size:26px; line-height:1.25; font-weight:600; letter-spacing:-0.012em;\n  margin:0 0 9px; color:#1C244B;\n}\n.ols-ice-001 p.ice-sub{\n  font-size:14.5px; line-height:1.62; font-weight:300; color:#4a5270;\n  margin:0; max-width:66ch;\n}\n\n.ols-ice-001 .ice-stage{\n  position:relative; 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padding:4px 8px;}\n  .ols-ice-001 .ice-caption{font-size:10.5px; padding:5px 9px; max-width:66%;}\n  .ols-ice-001 .ice-density{font-size:11.5px; padding:5px 10px;}\n  .ols-ice-001 .ice-info{padding:18px;}\n}\n@media (prefers-reduced-motion:reduce){\n  .ols-ice-001 .ice-seg button,.ols-ice-001 .ice-pill{transition:none;}\n}\n\n.ols-cc-ice-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-ice-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-ice-001 a:hover{text-decoration:underline;}\n<\/style>\n\n<div class=\"ice-head\">\n  <h2 class=\"ice-title\">The Open Hexagonal Lattice of Ice, and Why It Collapses on Melting<\/h2>\n  <p class=\"ice-sub\">Drag to rotate, scroll or pinch to zoom. Every molecule in the ice lattice is held by four hydrogen bonds in a tetrahedral arrangement, which forces open hexagonal channels through the solid. Switch to liquid water to watch the channels collapse.<\/p>\n<\/div>\n\n<div class=\"ice-stage\" id=\"iceStage\">\n  <canvas class=\"ice-canvas\" id=\"iceCanvas\"><\/canvas>\n  <div class=\"ice-overlay\" id=\"iceOverlay\"><\/div>\n  <div class=\"ice-caption\" id=\"iceCaption\"><\/div>\n  <div class=\"ice-hint\" id=\"iceHint\">Drag to rotate<\/div>\n  <div class=\"ice-density\" id=\"iceDensity\"><\/div>\n<\/div>\n\n<div class=\"ice-controls\">\n  <div class=\"ice-row\">\n    <span class=\"ice-rowlab\">State<\/span>\n    <div class=\"ice-seg\" role=\"group\" aria-label=\"State\">\n      <button type=\"button\" data-s=\"ice\" aria-pressed=\"true\">Ice<\/button>\n      <button type=\"button\" data-s=\"liq\" aria-pressed=\"false\">Liquid water<\/button>\n    <\/div>\n  <\/div>\n\n  <div class=\"ice-row\">\n    <span class=\"ice-rowlab\">View<\/span>\n    <div class=\"ice-seg\" role=\"group\" aria-label=\"Camera view\">\n      <button type=\"button\" data-v=\"front\" aria-pressed=\"false\">Front<\/button>\n      <button type=\"button\" data-v=\"corner\" aria-pressed=\"false\">Corner<\/button>\n      <button type=\"button\" data-v=\"top\" aria-pressed=\"false\">Top<\/button>\n    <\/div>\n  <\/div>\n\n  <div class=\"ice-row\">\n    <span class=\"ice-rowlab\">Show<\/span>\n    <button type=\"button\" class=\"ice-pill\" id=\"iceTogHb\" aria-pressed=\"true\"><i class=\"dot\"><\/i>Hydrogen bonds<\/button>\n    <button type=\"button\" class=\"ice-pill\" id=\"iceTogH\" aria-pressed=\"true\"><i class=\"dot\"><\/i>Hydrogen atoms<\/button>\n    <button type=\"button\" class=\"ice-pill p-amber\" id=\"iceTogRing\" aria-pressed=\"true\"><i class=\"dot\"><\/i>One hexagon<\/button>\n    <button type=\"button\" class=\"ice-pill\" id=\"iceTogLab\" aria-pressed=\"true\"><i class=\"dot\"><\/i>Labels<\/button>\n  <\/div>\n\n  <div class=\"ice-row\">\n    <span class=\"ice-rowlab\">Motion<\/span>\n    <button type=\"button\" class=\"ice-pill\" id=\"iceSpin\" aria-pressed=\"false\"><i class=\"dot\"><\/i>Rotation<\/button>\n    <button type=\"button\" class=\"ice-pill\" id=\"iceResetV\">Reset view<\/button>\n  <\/div>\n<\/div>\n\n<div class=\"ice-info\">\n  <h3 id=\"iceInfoTitle\"><\/h3>\n  <p id=\"iceInfoText\"><\/p>\n  <div class=\"ice-facts\" id=\"iceFacts\"><\/div>\n  <div class=\"ice-key\">\n    <span><i style=\"background:rgba(198,46,40,0.85)\"><\/i>Oxygen<\/span>\n    <span><i style=\"background:rgba(228,231,239,0.95)\"><\/i>Hydrogen<\/span>\n    <span><i style=\"background:rgba(37,99,235,0.6)\"><\/i>Hydrogen bond<\/span>\n    <span><i style=\"background:rgba(199,120,18,0.75)\"><\/i>One hexagonal ring<\/span>\n  <\/div>\n<\/div>\n<\/section>\n\n<p class=\"ols-cc-ice-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\/ice-lattice.js\"><\/script>\n<p>This has consequences beyond the exam: ice on a pond insulates the water below it, so aquatic life survives winter, and water expanding as it freezes shatters rocks and bursts pipes.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Ice is less dense than water because hydrogen bonds hold the water molecules in a fixed, open tetrahedral lattice with large spaces; when ice melts some hydrogen bonds break and the molecules move closer together.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Surface Tension<\/h2>\n<\/div>\n<p>Water has a high <strong>surface tension<\/strong> because the molecules at the surface are pulled inwards and sideways by hydrogen bonds to their neighbours, with no molecules above to balance the pull. The surface therefore behaves like a stretched skin that resists being broken or increased in area. This is why water forms near-spherical droplets, why a steel needle can be floated on water and why pond skaters walk on it.<\/p>\n<p>Liquids held only by induced dipole-dipole forces, such as hexane, have a much lower surface tension because far less energy is needed to create new surface. Adding a detergent to water lowers its surface tension by placing molecules at the surface that cannot hydrogen bond as strongly.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Surface tension is not named in the AQA specification, but it appears in data-response questions; explain it with the same hydrogen-bonding argument.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Other Consequences of Hydrogen Bonding in Water<\/h2>\n<\/div>\n<p>Water also has an unusually high specific heat capacity and a high enthalpy change of vaporisation, because energy supplied to water is used to break hydrogen bonds before the molecules can move faster or escape as a gas. These properties make water an excellent coolant and moderate the climate of coastal regions. Water is also an excellent solvent for ionic compounds and for molecules that can hydrogen bond, which the <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/choosing-solvents\/\">Choosing Solvents<\/a> page explains.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Property<\/th><th>Value for water<\/th><th>Comparison<\/th><th>Cause<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Boiling point<\/strong><\/td><td>100 \u00b0C<\/td><td>H\u2082S: -60 \u00b0C<\/td><td>four hydrogen bonds per molecule<\/td><\/tr>\n<tr><td><strong>Density of solid<\/strong><\/td><td>0.92 g cm\u207b\u00b3<\/td><td>liquid: 1.00 g cm\u207b\u00b3<\/td><td>open hydrogen-bonded lattice<\/td><\/tr>\n<tr><td><strong>Surface tension<\/strong><\/td><td>72 mN m\u207b\u00b9<\/td><td>hexane: 18 mN m\u207b\u00b9<\/td><td>surface molecules pulled inwards by hydrogen bonds<\/td><\/tr>\n<tr><td><strong>Specific heat capacity<\/strong><\/td><td>4.18 J g\u207b\u00b9 K\u207b\u00b9<\/td><td>ethanol: 2.44 J g\u207b\u00b9 K\u207b\u00b9<\/td><td>energy breaks hydrogen bonds before raising temperature<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Whatever the anomalous property, the answer begins &#8220;because water molecules form hydrogen bonds&#8221; and ends with what those bonds do.<\/p>\n<\/div>\n<\/article>\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 ice floats<\/h3><p>Hydrogen bonds hold molecules in an open tetrahedral lattice with spaces; on melting some bonds break and molecules move closer, so the liquid is denser.<\/p>\n<h3>Explain the boiling point of water compared with H\u2082S<\/h3><p>Hydrogen bonds between water molecules are stronger than the permanent dipole-dipole forces and induced dipole-dipole forces between H\u2082S molecules.<\/p>\n<h3>Why is CH\u2084 not anomalous?<\/h3><p>Carbon is not electronegative enough for C-H hydrogens to form hydrogen bonds.<\/p>\n<h3>Do not say<\/h3><p>&#8220;Ice has stronger hydrogen bonds than water&#8221; (the bonds are the same strength; ice has more of them held rigidly); &#8220;covalent bonds break when ice melts&#8221;.<\/p>\n<\/article>\n<section class=\"ols-h5p-card\">\n<h2>Check Your Understanding<\/h2>\n<p>Apply the hydrogen-bonding explanation to data and substances that are not discussed above.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-534\" class=\"h5p-iframe\" data-content-id=\"534\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"IMF Water Drag: lakes in winter\"><\/iframe><\/div><\/div>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-535\" class=\"h5p-iframe\" data-content-id=\"535\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"IMF Water MCQ: hydrogen selenide\"><\/iframe><\/div><\/div>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-536\" class=\"h5p-iframe\" data-content-id=\"536\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"IMF Water MCQ: maximum density\"><\/iframe><\/div><\/div>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-537\" class=\"h5p-iframe\" data-content-id=\"537\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"IMF Water MCQ: droplets on a leaf\"><\/iframe><\/div><\/div>\n<\/section>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Use these quick answers to check the explanations for water that AQA questions ask for.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Why is the boiling point of water so high?<\/h3>\n<p>Each water molecule can form up to four hydrogen bonds, which are far stronger than the permanent dipole-dipole forces and induced dipole-dipole forces holding together hydrides such as H\u2082S. Extending the Group 6 trend would predict about -80 \u00b0C; water boils at 100 \u00b0C.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why does ice float on water?<\/h3>\n<p>In ice the hydrogen bonds hold each molecule to four neighbours in a fixed tetrahedral arrangement, building an open hexagonal lattice with large spaces. When ice melts some hydrogen bonds break and the molecules move closer together, so the liquid is denser.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is methane not anomalous?<\/h3>\n<p>Carbon is not electronegative enough for the hydrogen atoms in CH\u2084 to carry a large \u03b4+ charge, so methane cannot hydrogen bond. The Group 4 hydrides follow a smooth trend set by their number of electrons.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why does water have a high surface tension?<\/h3>\n<p>Molecules at the surface have no neighbours above them, so the hydrogen bonds pull them inwards and sideways. Making new surface therefore costs energy, which is why water forms beads and supports a floating needle.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Are the hydrogen bonds in ice stronger than in water?<\/h3>\n<p>No, they are the same strength. Ice simply has more of them and holds them in fixed positions, which is what produces the open structure.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<section class=\"ols-related-card\">\n<h2>Related Intermolecular Forces 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\/aqa\/3-1-3-bonding\/intermolecular-forces\/london-forces\/\">London Forces<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/permanent-dipole-dipole-forces\/\">Permanent Dipole-Dipole Forces<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/hydrogen-bonding\/\">Hydrogen Bonding<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/boiling-temperature-trends\/\">Boiling Point Trends<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/aqa\/3-1-3-bonding\/intermolecular-forces\/choosing-solvents\/\">Choosing Solvents<\/a>\n<\/div>\n<\/section>\n<section class=\"ols-attribution-card\">\n        <p><strong>Copyright and author footprint:<\/strong> This OLS revision page was written for Online Learning System by <strong>Dr. Mohammed Al-Fatah<\/strong>. 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