{"id":10484,"date":"2026-09-26T11:30:40","date_gmt":"2026-09-26T10:30:40","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/trends-in-the-halogens\/"},"modified":"2026-10-04T23:02:49","modified_gmt":"2026-10-04T22:02:49","slug":"trends-in-the-halogens","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/trends-in-the-halogens\/","title":{"rendered":"Trends in the Halogens"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-redox-groups-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 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   margin: 0 0 8px;\n      font-size: 20px;\n      line-height: 1.3;\n      color: var(--navy);\n    }\n.ols-faq-item p {\n      margin: 0;\n      font-size: 16px;\n      line-height: 1.65;\n      color: var(--body-text);\n    }\n.ols-faq-card,\n      .ols-quicksnap-card,\n      .ols-attribution-card {\n        padding: 24px 18px;\n        border-radius: 22px;\n      }\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 8 Redox &amp; Groups 1, 2 and 7<\/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-8-redox-chemistry-and-groups-1-2-and-7\/\">Topic 8 Overview<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8a-redox-chemistry\/\">Topic 8A Redox Chemistry<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8a-redox-chemistry\/oxidation-numbers\/\">Oxidation Numbers<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8a-redox-chemistry\/electron-transfer-and-half-equations\/\">Electron Transfer and Half-Equations<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8a-redox-chemistry\/disproportionation\/\">Disproportionation<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8a-redox-chemistry\/redox-classification\/\">Redox Classification<\/a>\n          <\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8b-groups-1-and-2\/\">Topic 8B Groups 1 and 2<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8b-groups-1-and-2\/trends-down-groups-1-and-2\/\">Trends Down Groups 1 and 2<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8b-groups-1-and-2\/reactions-of-the-group-1-and-2-elements\/\">Reactions of the Group 1 and 2 Elements<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8b-groups-1-and-2\/oxides-hydroxides-and-carbonates\/\">Oxides, Hydroxides and Carbonates<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8b-groups-1-and-2\/solubility-trends-and-the-sulfate-test\/\">Solubility Trends and the Sulfate Test<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8b-groups-1-and-2\/thermal-stability-and-flame-colours\/\">Thermal Stability and Flame Colours<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8b-groups-1-and-2\/tests-for-ions\/\">Tests for Ions<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8b-groups-1-and-2\/titrations-and-measurement-uncertainty\/\">Titrations and Measurement Uncertainty<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-3-concentration-of-hcl-by-titration\/\">Core Practical 3<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/cp-4-preparation-of-a-standard-solution\/\">Core Practical 4<\/a>\n          <\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/\">Topic 8C Group 7<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/trends-in-the-halogens\/\">Trends in the Halogens<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/halogens-as-oxidising-agents\/\">Halogens as Oxidising Agents<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/disproportionation-reactions-of-chlorine\/\">Disproportionation Reactions of Chlorine<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/halide-ions-reducing-agents-and-tests\/\">Halide Ions: Reducing Agents and Tests<\/a>\n          <\/li>\n        <\/ul>\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-6-energetics\/\">Topic 6 Energetics<\/a>\n      <\/li>\n      <li>\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      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-2-atomic-structure-and-the-periodic-table\/\">Topic 2 Atomic Structure &amp; The Periodic Table<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/core-practicals\/\">Core Practicals<\/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      .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    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href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/\">Topic 8 Redox Chemistry and Groups 1, 2 and 7<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/\">Topic 8C Group 7<\/a> \/\n<span>Trends in the Halogens<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Trends in the Halogens<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to the trends in Group 7: physical states and colours, melting and boiling points from London forces, electronegativity, bond strength and volatility, the fall in reactivity down the group, and predictions for fluorine and astatine.<\/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 8C Group 7<\/div>\n<\/div>\n        <div class=\"ols-author\">\n\n    <img decoding=\"async\"\n      class=\"ols-author-avatar-img\"\n      src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n      alt=\"Dr. Mohammed Al-Fatah\"\n    >\n\n    <div class=\"ols-author-content\">\n\n      <h2 class=\"ols-author-title\">\n        Written by: Dr. Mohammed Al-Fatah\n      <\/h2>\n\n      <p class=\"ols-author-description\">\n        Chemistry specialist revision notes for A Level Chemistry.\n      <\/p>\n\n      <a class=\"ols-linkedin-pill\" href=\"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\" target=\"_blank\" rel=\"noopener noreferrer\">\n        <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      <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: The Halogens<\/h2>\n<p>Three quick questions on the halogens as you met them at GCSE: their outer shell, the ions they form and the family name.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"885\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>Physical States and Colours<\/h2>\n<\/div>\n<p>The <strong>halogens<\/strong> (Group 7) are non-metals that exist as diatomic molecules, X\u2082, held together by a single covalent bond.<\/p>\n<p>Each atom has seven outer electrons (ns\u00b2 np\u2075), so a halogen atom gains one electron in most of its reactions to form a halide ion, X\u207b. Each element is one electron short of the noble gas after it.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Element<\/th><th>State at room temperature<\/th><th>Colour<\/th><th>Boiling point \/ \u00b0C<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Fluorine, F\u2082<\/strong><\/td><td>gas<\/td><td>pale yellow<\/td><td>\u2212188<\/td><\/tr>\n<tr><td><strong>Chlorine, Cl\u2082<\/strong><\/td><td>gas<\/td><td>pale green<\/td><td>\u221234<\/td><\/tr>\n<tr><td><strong>Bromine, Br\u2082<\/strong><\/td><td>liquid<\/td><td>red-brown (orange vapour)<\/td><td>59<\/td><\/tr>\n<tr><td><strong>Iodine, I\u2082<\/strong><\/td><td>solid<\/td><td>grey-black (purple vapour)<\/td><td>184<\/td><\/tr>\n<tr><td><strong>Astatine, At\u2082<\/strong><\/td><td>solid (predicted)<\/td><td>black (predicted)<\/td><td>about 300 (predicted)<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The colours darken and the boiling points rise down the group, so the elements go from gas to liquid to solid. Iodine sublimes on gentle warming, going straight from the solid to a purple vapour.<\/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\/redox-groups-trends-in-the-halogens.png\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/redox-groups-trends-in-the-halogens.png\" alt=\"Trends in the halogens: state, colour, boiling point and electronegativity\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/redox-groups-trends-in-the-halogens.png\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>The strip shows the three trends together: colour deepening and boiling point rising down the group while electronegativity falls.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Learn the states and colours. Bromine is the only liquid non-metal element, and iodine vapour is purple, not brown.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>Melting and Boiling Points<\/h2>\n<\/div>\n<p>The halogen molecules are non-polar, so the only forces between them are <strong>London forces<\/strong> (instantaneous dipole\u2013induced dipole forces).<\/p>\n<p>Down the group each molecule has more electrons, so the instantaneous dipoles are larger and the London forces are stronger. More energy is needed to separate the molecules, and <strong>the melting and boiling points increase down the group<\/strong>.<\/p>\n<p>The covalent bond inside each molecule is not broken on boiling, so its strength is irrelevant to the boiling point. Answers that mention &#8220;stronger bonds&#8221; for the boiling point trend lose the mark.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Iodine has a higher boiling point than chlorine because iodine molecules have more electrons, so the London forces between them are stronger and more energy is needed to overcome 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>Check: Volatility Down the Group<\/h2>\n<p>Explain the state and boiling point of a halogen from its electron count, and spot the answer that confuses covalent bonds with intermolecular forces.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-886\" class=\"h5p-iframe\" data-content-id=\"886\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Redox and Groups MCQ: Volatility Down the Group\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>Electronegativity<\/h2>\n<\/div>\n<p><strong>Electronegativity decreases down the group.<\/strong> Fluorine, at 4.0 on the Pauling scale, is the most electronegative element of all; chlorine is 3.0, bromine 2.8 and iodine 2.5.<\/p>\n<p>Down the group the bonding pair in a covalent bond is further from the halogen nucleus and shielded by more inner shells. The nucleus attracts it less strongly, and the higher nuclear charge does not make up the difference.<\/p>\n<p>The same argument explains why the halogens become weaker <strong>oxidising agents<\/strong> down the group: an atom that attracts a bonding pair less strongly also attracts an extra electron less strongly.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Element<\/th><th>Electronegativity<\/th><th>Atomic radius \/ pm<\/th><th>X\u2013X bond enthalpy \/ kJ mol\u207b\u00b9<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>F<\/strong><\/td><td>4.0<\/td><td>71<\/td><td>158<\/td><\/tr>\n<tr><td><strong>Cl<\/strong><\/td><td>3.0<\/td><td>99<\/td><td>243<\/td><\/tr>\n<tr><td><strong>Br<\/strong><\/td><td>2.8<\/td><td>114<\/td><td>193<\/td><\/tr>\n<tr><td><strong>I<\/strong><\/td><td>2.5<\/td><td>133<\/td><td>151<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Electronegativity, oxidising power and reactivity all fall down the group for the same reason: the outer shell is further from the nucleus and more shielded.<\/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>Reactivity Down the Group<\/h2>\n<\/div>\n<p>A halogen reacts by gaining an electron to complete its outer shell. <strong>Reactivity decreases down the group<\/strong> because the incoming electron enters a shell further from the nucleus, shielded by more inner electrons, so it is less strongly attracted.<\/p>\n<p>Fluorine is the most reactive element; iodine reacts only slowly and often reversibly.<\/p>\n<p>The trend shows most clearly in the displacement reactions, where a more reactive halogen takes electrons from the ions of a less reactive one. These are treated on the <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/halogens-as-oxidising-agents\/\">Halogens as Oxidising Agents<\/a> page.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Reactivity decreases down the group because the atomic radius and shielding increase, so the nucleus attracts an incoming electron less strongly and a halide ion forms less readily.<\/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>Check: Explaining the Reactivity Trend<\/h2>\n<p>Choose the complete explanation for the falling reactivity of the halogens and correct an incomplete one.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-887\" class=\"h5p-iframe\" data-content-id=\"887\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Redox and Groups MCQ: Explaining the Reactivity Trend\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Predicting Fluorine and Astatine<\/h2>\n<\/div>\n<p>Trends allow predictions about the elements at each end of the group.<\/p><p><strong>Fluorine<\/strong> is a pale yellow gas, the strongest oxidising agent of the group. It is so reactive that it attacks water and glass, and it forms only the \u22121 oxidation number because nothing is more electronegative.<\/p><p>Its hydride, HF, is a weak acid with hydrogen bonding between its molecules.<\/p><p><strong>Astatine<\/strong> is predicted to be a black solid with a high boiling point, the weakest oxidising agent of the group, displaced from its salts by every other halogen.<\/p><p>It is predicted to form a silver salt that is insoluble and does not dissolve in ammonia, and to have positive oxidation numbers in its compounds with oxygen.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Property<\/th><th>Fluorine (top)<\/th><th>Astatine (bottom)<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>State and colour<\/strong><\/td><td>pale yellow gas<\/td><td>black solid<\/td><\/tr>\n<tr><td><strong>Oxidising power<\/strong><\/td><td>strongest<\/td><td>weakest<\/td><\/tr>\n<tr><td><strong>Displacement<\/strong><\/td><td>displaces all other halogens<\/td><td>displaced by all other halogens<\/td><\/tr>\n<tr><td><strong>Reaction with hydrogen<\/strong><\/td><td>explosive even in the dark<\/td><td>very slow, reversible<\/td><\/tr>\n<tr><td><strong>Silver halide<\/strong><\/td><td>soluble, no precipitate<\/td><td>insoluble, insoluble in ammonia<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Technique point:<\/strong> A prediction question wants the trend, the value at the nearest known element, and the predicted value. &#8220;Iodine is a solid, so astatine, which is lower, will also be a solid with a higher melting point.&#8221;<\/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\/t8x-fatpredict.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\/t8x-fatpredict.jpg\" alt=\"Comparison of fluorine and predicted astatine properties at the two ends of the halogen group, with a prediction method.\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/t8x-fatpredict.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Following each trend to the ends of the group predicts fluorine as the strongest oxidising agent and astatine as a black solid that is the weakest.<\/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>Check: Predictions from Trends<\/h2>\n<p>Use the trends to predict properties of astatine and fluorine that are not listed in the table above.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-888\" class=\"h5p-iframe\" data-content-id=\"888\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Redox and Groups Quick Answers: Predictions from Trends\"><\/iframe><\/div><\/div>\n<\/section>\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 the trend in boiling points<\/h3><p>More electrons per molecule down the group give stronger London forces, so more energy is needed to separate the molecules.<\/p>\n<h3>Explain the trend in electronegativity<\/h3><p>The bonding pair is further from the nucleus and more shielded down the group, so it is less strongly attracted.<\/p>\n<h3>Predict a property of astatine<\/h3><p>Continue the trend from iodine: solid, dark, least reactive, weakest oxidising agent.<\/p>\n<h3>Do not say<\/h3><p>&#8220;Stronger bonds so higher boiling point&#8221;; &#8220;iodine vapour is brown&#8221;; &#8220;fluorine is less reactive because it is small&#8221;.<\/p>\n<\/article>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Use these quick answers to check the trends in the Group 7 elements.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Why do the boiling points increase down the group?<\/h3>\n<p>The molecules have more electrons, so the London forces between them are stronger and more energy is needed to separate them.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why does electronegativity decrease down the group?<\/h3>\n<p>The bonding pair is further from the nucleus and more shielded, so the nucleus attracts it less strongly.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why is fluorine the most reactive halogen?<\/h3>\n<p>Its outer shell is closest to the nucleus and least shielded, so it attracts an extra electron most strongly.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What colour is iodine vapour?<\/h3>\n<p>Purple. The solid is grey-black and its solution in water is brown, but the vapour is purple.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What can I predict about astatine?<\/h3>\n<p>It is below iodine, so it should be a dark solid with a higher boiling point, the weakest oxidising agent of the group, and displaced from its salts by every other halogen.<\/p>\n<\/div>\n<\/div>\n<\/section>\n<section class=\"ols-related-card\">\n<h2>Related Topic 8C Group 7 Pages<\/h2>\n<p>Use these pages to connect the ideas across Group 7 and the rest of Topic 8.<\/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-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/halogens-as-oxidising-agents\/\">Halogens as Oxidising Agents<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/disproportionation-reactions-of-chlorine\/\">Disproportionation Reactions of Chlorine<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/halide-ions-reducing-agents-and-tests\/\">Halide Ions: Reducing Agents and Tests<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/\">Topic 8C Group 7 Overview<\/a>\n<\/div>\n<\/section>\n<section class=\"ols-attribution-card\">\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-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/trends-in-the-halogens\/#webpage\",\n      \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel-international\/topic-8-redox-chemistry-and-groups-1-2-and-7\/8c-group-7\/trends-in-the-halogens\/\",\n      \"name\": \"Trends in the Halogens | Topic 8C Group 7 | Online Learning System\",\n      \"description\": \"Edexcel International A Level Chemistry revision notes on the trends in Group 7: states, colours, boiling points, electronegativity, reactivity and predictions for fluorine and astatine.\",\n 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