{"id":4833,"date":"2026-06-03T06:24:35","date_gmt":"2026-06-03T05:24:35","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/"},"modified":"2026-10-25T12:07:58","modified_gmt":"2026-10-25T12:07:58","slug":"free-radical-substitution","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/","title":{"rendered":"Free Radical Substitution"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-free-radical-substitution-page\">\n  <style>\n    .ols-revision-page {\n      --navy: #1C244B;\n      --blue: #2563eb;\n      --soft-blue: #eef4ff;\n      --soft-red: #fff7f7;\n      --soft-purple: #f7f0ff;\n      --soft-green: #f0f7f1;\n      --soft-yellow: #fff8e6;\n      --red: #c81e1e;\n      --gold: 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24px 18px;\n        border-radius: 22px;\n      }\n\n      .ols-note-title {\n        align-items: flex-start;\n      }\n\n      .ols-figure-card {\n        border-radius: 22px;\n      }\n\n      .ols-figure-image {\n        min-height: 230px;\n        padding: 14px;\n      }\n\n      .ols-figure-caption {\n        padding: 18px;\n      }\n\n      .ols-related-grid,\n      .ols-infographic-grid {\n        grid-template-columns: 1fr;\n      }\n\n      .ols-table-wrap {\n        border-radius: 20px;\n        overflow: hidden;\n      }\n\n      .ols-table,\n      .ols-table thead,\n      .ols-table tbody,\n      .ols-table th,\n      .ols-table td,\n      .ols-table tr {\n        display: block;\n        width: 100%;\n      }\n\n      .ols-table thead {\n        display: none;\n      }\n\n      .ols-table tr {\n        border-bottom: 1px solid var(--border);\n        background: #ffffff;\n      }\n\n      .ols-table tr:last-child {\n        border-bottom: none;\n      }\n\n      .ols-table td {\n        display: grid;\n        grid-template-columns: minmax(120px, 38%) minmax(0, 1fr);\n        gap: 12px;\n        align-items: start;\n        border-bottom: 1px solid rgba(28, 36, 75, 0.08);\n        padding: 14px;\n        overflow-wrap: anywhere;\n      }\n\n      .ols-table td:last-child {\n        border-bottom: none;\n      }\n\n      .ols-table td::before {\n        content: attr(data-label);\n        font-weight: 700;\n        color: var(--navy);\n        overflow-wrap: anywhere;\n      }\n\n      .ols-infographic-full {\n        margin: 0 0 26px;\n      }\n\n      .ols-infographic-full-frame {\n        border-radius: 18px;\n      }\n    }\n  <\/style>\n\n  <aside class=\"ols-sidebar\">\r\n  <div class=\"ols-sidebar-header\">\r\n    <h3>Revision Notes<\/h3>\r\n    <p>A Level Chemistry<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Topic 6 Organic Chemistry I<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/\">Introduction to Organic Chemistry<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/iupac-rules\/\">IUPAC Rules<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/alkene\/\">Alkene<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/alcohol\/\">Alcohol<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/halogenoalkanes\/\">Halogenoalkanes<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/aldehyde\/\">Aldehyde<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/ketone\/\">Ketone<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/carboxylic-acid\/\">Carboxylic Acid<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/ester\/\">Ester<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/introduction-to-organic-chemistry\/isomerism\/\">Isomerism<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/\">Alkanes<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/\">Alkanes from Crude Oil<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/fractional-distillation\/\">Fractional Distillation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/cracking\/\">Cracking<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/crude-oil\/reforming\/\">Reforming<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/\">Alkanes as Fuel<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/combustion\/\">Combustion<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/oxides-of-sulfur\/\">Oxides of Sulfur<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/oxides-of-nitrogen\/\">Oxides of Nitrogen<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/catalytic-converter\/\">Catalytic Converter<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/alternative-fuel\/\">Alternative Fuel<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/\">Reactions of Alkanes<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/\">Free Radical Substitution<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/initiation\/\">Initiation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/propagation\/\">Propagation<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/termination\/\">Termination<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/further-substitution\/\">Further Substitution<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/\">Alkenes<\/a>\r\n\r\n        <ul class=\"ols-subtopic-list\">\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/alkene-bonding\/\">Alkene Bonding<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/geometric-isomerism\/\">Geometric Isomerism<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/electrophilic-addition-mechanism\/\">Electrophilic Addition Mechanism<\/a>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/\">Reactions of Alkenes<\/a>\r\n\r\n            <ul class=\"ols-subtopic-list\">\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/halogens\/\">Halogens<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/hydrogen-halide\/\">Hydrogen Halide<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/bromine-water\/\">Bromine Water<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/hydrogen\/\">Hydrogen<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/steam\/\">Steam<\/a>\r\n              <\/li>\r\n              <li>\r\n                <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/reactions-of-alkenes\/kmno4\/\">KMnO4<\/a>\r\n              <\/li>\r\n            <\/ul>\r\n          <\/li>\r\n\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/polymerisation-reactions\/\">Polymerisation Reactions<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/polymer-waste\/\">Polymer Waste<\/a>\r\n          <\/li>\r\n        <\/ul>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/halogenoalkanes\/\">Halogenoalkanes<\/a>\r\n      <\/li>\r\n\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alcohols\/\">Alcohols<\/a>\r\n      <\/li>\r\n\r\n    <\/ul>\r\n  <\/div>\r\n\r\n  <div class=\"ols-topic-group\">\r\n    <h4>Next Topics<\/h4>\r\n\r\n    <ul class=\"ols-topic-list\">\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-7-modern-analytical-techniques-i\/\">Topic 7 Modern Analytical Techniques I<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/\">Topic 5 Formulae, Equations &amp; Amounts<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/\">Topic 4 Inorganic Chemistry &amp; The Periodic Table<\/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\"], a[aria-current]').forEach(function(a) {\r\n      a.removeAttribute('aria-current');\r\n      a.removeAttribute('tabindex');\r\n      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{\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\/edexcel\/\">Edexcel<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/\">Topic 6 Organic Chemistry I<\/a> \/\n        <span>Free Radical Substitution<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Free Radical Substitution<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to why alkanes are usually unreactive, how they react with halogens under ultraviolet light, and how free-radical substitution is introduced through initiation, propagation and termination.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Paper 2<\/div>\n          <div class=\"ols-badge\">Topic 6: Organic Chemistry I<\/div>\n          <div class=\"ols-badge\">9CH0\/02<\/div>\n        <\/div>\n      <\/header>\n<!-- 3D card: radical-chain-methane (5 Oct 2026, Topics 1-5 upgrade) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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text-align:center; font-size:11px; font-style:italic; color:#aab0c0;\n}\n.ols-cc-radc-001 a{color:#aab0c0; text-decoration:none;}\n.ols-cc-radc-001 a:hover{text-decoration:underline;}\n.ols-radc-001 .radc-seg button{display:inline-flex; align-items:center;}\n.ols-radc-001 .radc-seg button .radc-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-radc-001 .radc-seg button[aria-pressed=\"true\"] .radc-n{background:#ffffff; color:#2563eb;}\n<\/style>\n\n<div class=\"radc-head\">\n  <h2 class=\"radc-title\">Radical Chain Reaction: Methane and Chlorine<\/h2>\n  <p class=\"radc-sub\">Choose a step to follow every electron: UV light makes the radicals, the chain repeats, and two radicals meeting end it.<\/p>\n<\/div>\n\n<div class=\"radc-stage\" id=\"radcStage\">\n  <canvas class=\"radc-canvas\" id=\"radcCanvas\"><\/canvas>\n  <div class=\"radc-overlay\" id=\"radcOverlay\"><\/div>\n  <div class=\"radc-caption\" id=\"radcCaption\"><\/div>\n  <div class=\"radc-hint\" id=\"radcHint\">Drag to rotate<\/div>\n  <div class=\"radc-badges\" id=\"radcBadges\"><\/div>\n<\/div>\n\n<div class=\"radc-controls\">\n  <div class=\"radc-row\">\n    <span class=\"radc-rowlab\">Step<\/span>\n    <div class=\"radc-seg\" role=\"group\" aria-label=\"Step\">\n      <button type=\"button\" data-step=\"1\" aria-pressed=\"true\"><span class=\"radc-n\">1<\/span>Initiation<\/button>\n      <button type=\"button\" data-step=\"2\" aria-pressed=\"false\"><span class=\"radc-n\">2<\/span>Cl\u2022 takes an H<\/button>\n      <button type=\"button\" data-step=\"3\" aria-pressed=\"false\"><span class=\"radc-n\">3<\/span>\u2022CH\u2083 takes a Cl<\/button>\n      <button type=\"button\" data-step=\"4\" aria-pressed=\"false\"><span class=\"radc-n\">4<\/span>The chain repeats<\/button>\n      <button type=\"button\" data-step=\"5\" aria-pressed=\"false\"><span class=\"radc-n\">5<\/span>Termination<\/button>\n    <\/div>\n  <\/div>\n\n  <div class=\"radc-row\">\n    <span class=\"radc-rowlab\">View<\/span>\n    <button type=\"button\" class=\"radc-pill\" id=\"radcResetV\">Reset view<\/button>\n  <\/div>\n<\/div>\n\n<div class=\"radc-info\">\n  <h3 id=\"radcInfoTitle\"><\/h3>\n  <p id=\"radcInfoText\"><\/p>\n  <div class=\"radc-facts\" id=\"radcFacts\"><\/div>\n  <div class=\"radc-key\">\n    <span><i class=\"k-ball\" style=\"background:#464a54\"><\/i>Carbon<\/span>\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:#f6c426\"><\/i>Electron<\/span>\n  <\/div>\n<\/div>\n\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/radical-chain-methane.js?v=20261025p\"><\/script>\n<\/section>\n\n<p class=\"ols-cc-radc-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\n\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 in an Alkane<\/h2>\n<p>Start with the GCSE ideas about shared electron pairs in alkanes.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"724\"><\/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>Why Alkanes Are Usually Unreactive<\/h2>\n        <\/div>\n\n        <p>Alkanes are saturated hydrocarbons. They contain only carbon and hydrogen atoms, with only single covalent bonds between atoms.<\/p>\n        <p>In most situations, alkanes <strong>do not react readily<\/strong> with other substances because they contain strong <strong>carbon-carbon, C-C,<\/strong> and <strong>carbon-hydrogen, C-H,<\/strong> bonds.<\/p>\n        <p>These strong covalent bonds require a large amount of energy to break. As a result, alkanes usually need <strong>high-energy conditions<\/strong>, such as ultraviolet light or high temperature, before they react.<\/p>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Key idea:<\/strong> Alkane reactions are not easy to start because the C-C and C-H bonds are strong and non-polar or only weakly 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: Why Nothing Happens to Hexane<\/h2>\n<p>Choose the best explanation of why an alkane does not react with common reagents.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-133\" class=\"h5p-iframe\" data-content-id=\"133\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Free Radical Substitution MCQ: Why Hexane Is Left Unchanged\"><\/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>Alkanes React with Halogens Under UV Light<\/h2>\n        <\/div>\n\n        <p>Although alkanes are generally unreactive, they can react with <strong>halogens<\/strong> under specific conditions.<\/p>\n        <p>When exposed to <strong>ultraviolet, UV, light<\/strong>, alkanes react with chlorine in a <strong>substitution reaction<\/strong>. A hydrogen atom in the alkane is replaced by a chlorine atom.<\/p>\n        <p>For methane and chlorine, the overall equation can be written as:<\/p>\n\n        <div class=\"ols-definition-box\">\n          <p><strong>Overall reaction:<\/strong> CH<sub>4<\/sub> + Cl<sub>2<\/sub> \u2192 CH<sub>3<\/sub>Cl + HCl<\/p>\n        <\/div>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Important:<\/strong> This overall equation is a simplified summary. In practice, a more complex mixture of products can form because further substitution may occur.<\/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: Ethane and Bromine<\/h2>\n<p>Complete the passage about an alkane reacting with a halogen in UV light.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-132\" class=\"h5p-iframe\" data-content-id=\"132\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Free Radical Substitution Drag: Ethane and Bromine in Ultraviolet Light\"><\/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>What Is Free-Radical Substitution?<\/h2>\n        <\/div>\n\n        <p>Free-radical substitution is a mechanism in which highly reactive <strong>free radicals<\/strong> are produced and used to replace hydrogen atoms in an alkane with halogen atoms.<\/p>\n        <p>A <strong>free radical<\/strong> is a species that contains an <strong>unpaired electron<\/strong>. In equations, this unpaired electron is shown using a dot, such as Cl\u2022.<\/p>\n        <p>The mechanism does not occur as one simple step. It takes place through a sequence of distinct stages:<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Stage<\/th>\n                <th>What happens<\/th>\n                <th>Why it matters<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Stage\"><strong>Initiation<\/strong><\/td>\n                <td data-label=\"What happens\">UV light breaks a halogen-halogen bond to form free radicals.<\/td>\n                <td data-label=\"Why it matters\">This starts the chain reaction by producing reactive species.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Stage\"><strong>Propagation<\/strong><\/td>\n                <td data-label=\"What happens\">Free radicals react and generate new free radicals.<\/td>\n                <td data-label=\"Why it matters\">This repeating stage allows the chain reaction to continue.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Stage\"><strong>Termination<\/strong><\/td>\n                <td data-label=\"What happens\">Two free radicals combine together.<\/td>\n                <td data-label=\"Why it matters\">This removes radicals from the reaction mixture and stops that chain.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-key-box\">\n          <p><strong>Exam focus:<\/strong> Use the phrase <strong>free-radical substitution mechanism<\/strong> and link it to hydrogen atoms in alkanes being replaced by halogen atoms.<\/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\/10\/t4-img-31-radicalchain.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-31-radicalchain.jpg\" alt=\"Overview of free-radical substitution: UV splits Cl\u2082, a two-step propagation wheel regenerates Cl\u2022, and radicals meeting end the chain\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-31-radicalchain.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Initiation makes radicals, propagation keeps the chain going and termination removes radicals.<\/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 the Stage<\/h2>\n<p>Decide quickly which stage of the mechanism each equation shows.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-135\" class=\"h5p-iframe\" data-content-id=\"135\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Free Radical Substitution Quick Fire: Initiation, Propagation or Termination?\"><\/iframe><\/div><\/div>\n<\/section>\n\n\n      <article class=\"ols-note-card green\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">4<\/div>\n          <h2>Homolytic Fission and Free Radicals<\/h2>\n        <\/div>\n\n        <p>The first key idea in free-radical substitution is <strong>homolytic fission<\/strong>. This occurs when a covalent bond breaks so that each atom takes one electron from the shared pair.<\/p>\n        <p>When chlorine molecules absorb UV light, the Cl-Cl bond breaks by homolytic fission. This forms two chlorine radicals:<\/p>\n\n        <div class=\"ols-definition-box\">\n          <p><strong>Homolytic fission:<\/strong> Cl<sub>2<\/sub> \u2192 2Cl\u2022<\/p>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-cd-05-homolytic.svg\" alt=\"Homolytic fission: fish-hook arrows from the centre of X\u2013Y and of Cl\u2013Cl, giving two radicals each with one unpaired electron\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>Each atom receives one electron from the shared pair, forming two species with unpaired electrons.<\/p>\n          <\/div>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Spot the Radicals<\/h2>\n<p>Click every species that is a free radical.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-725\" class=\"h5p-iframe\" data-content-id=\"725\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Free Radical Substitution Mark the Words: Radical, Ion or Molecule?\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card yellow\">\n        <div class=\"ols-note-title\">\n          <div class=\"ols-note-icon\">5<\/div>\n          <h2>Homolytic Fission Compared with Heterolytic Fission<\/h2>\n        <\/div>\n\n        <p>Reaction mechanisms often involve bond breaking. The type of bond breaking depends on how the bonding electrons are divided.<\/p>\n        <p>In <strong>homolytic fission<\/strong>, each atom takes one electron and free radicals form. In <strong>heterolytic fission<\/strong>, one atom takes both electrons and ions form.<\/p>\n\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Type of fission<\/th>\n                <th>Electron movement<\/th>\n                <th>Products formed<\/th>\n                <th>Arrow style<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Type of fission\"><strong>Homolytic fission<\/strong><\/td>\n                <td data-label=\"Electron movement\">Each atom takes one electron from the shared pair.<\/td>\n                <td data-label=\"Products formed\">Free radicals.<\/td>\n                <td data-label=\"Arrow style\">Single-headed curly arrows are used for movement of one electron.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Type of fission\"><strong>Heterolytic fission<\/strong><\/td>\n                <td data-label=\"Electron movement\">One atom takes both electrons from the shared pair.<\/td>\n                <td data-label=\"Products formed\">Ions.<\/td>\n                <td data-label=\"Arrow style\">Double-headed curly arrows are used for movement of an electron pair.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-cd-06-heterolytic.svg\" alt=\"Heterolytic fission: a curly arrow from the centre of X\u2013Y and of H\u2013Cl to the more electronegative atom, giving a cation and an anion\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>Heterolytic fission produces ions because both bonding electrons move to the same atom.<\/p>\n          <\/div>\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\/10\/t4-img-32-twofissions.jpg\" target=\"_blank\" rel=\"noopener\" aria-label=\"Open image fullscreen\">\n<img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-32-twofissions.jpg\" alt=\"Comparison of homolytic and heterolytic fission: how the electrons divide, the products, the arrow type and typical bonds\" data-fullscreen-src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-img-32-twofissions.jpg\">\n<\/a>\n<\/div>\n<div class=\"ols-figure-caption\"><p>Homolytic fission gives radicals and uses single-headed arrows; heterolytic fission gives ions and uses double-headed arrows.<\/p><\/div>\n<\/div>\n<\/article>\n<!-- 3D card: bond-fission-homolytic-heterolytic (22 Oct 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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text-align:center; font-size:11px; font-style:italic; color:#aab0c0;\r\n}\r\n.ols-cc-bfi-001 a{color:#aab0c0; text-decoration:none;}\r\n.ols-cc-bfi-001 a:hover{text-decoration:underline;}\r\n.ols-bfi-001 .bfi-seg button{display:inline-flex; align-items:center;}\r\n.ols-bfi-001 .bfi-seg button .bfi-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;}\r\n.ols-bfi-001 .bfi-seg button[aria-pressed=\"true\"] .bfi-n{background:#ffffff; color:#2563eb;}\r\n<\/style>\r\n\r\n<div class=\"bfi-head\">\r\n  <h2 class=\"bfi-title\">Breaking a Covalent Bond: Homolytic and Heterolytic Fission<\/h2>\r\n  <p class=\"bfi-sub\">Choose a step to watch where the two electrons of a bond go when it breaks: one each (free radicals), or both to one atom (ions).<\/p>\r\n<\/div>\r\n\r\n<div class=\"bfi-stage\" id=\"bfiStage\">\r\n  <canvas class=\"bfi-canvas\" id=\"bfiCanvas\"><\/canvas>\r\n  <div class=\"bfi-overlay\" id=\"bfiOverlay\"><\/div>\r\n  <div class=\"bfi-caption\" id=\"bfiCaption\"><\/div>\r\n  <div class=\"bfi-hint\" id=\"bfiHint\">Drag to rotate<\/div>\r\n  <div class=\"bfi-badges\" id=\"bfiBadges\"><\/div>\r\n<\/div>\r\n\r\n<div class=\"bfi-controls\">\r\n  <div class=\"bfi-row\">\r\n    <span class=\"bfi-rowlab\">Step<\/span>\r\n    <div class=\"bfi-seg\" role=\"group\" aria-label=\"Step\">\r\n      <button type=\"button\" data-step=\"1\" aria-pressed=\"true\"><span class=\"bfi-n\">1<\/span>A shared pair<\/button>\r\n      <button type=\"button\" data-step=\"2\" aria-pressed=\"false\"><span class=\"bfi-n\">2<\/span>Homolytic fission<\/button>\r\n      <button type=\"button\" data-step=\"3\" aria-pressed=\"false\"><span class=\"bfi-n\">3<\/span>Heterolytic fission<\/button>\r\n      <button type=\"button\" data-step=\"4\" aria-pressed=\"false\"><span class=\"bfi-n\">4<\/span>Radicals and electrophiles<\/button>\r\n    <\/div>\r\n  <\/div>\r\n\r\n  <div class=\"bfi-row\">\r\n    <span class=\"bfi-rowlab\">View<\/span>\r\n    <button type=\"button\" class=\"bfi-pill\" id=\"bfiResetV\">Reset view<\/button>\r\n  <\/div>\r\n<\/div>\r\n\r\n<div class=\"bfi-info\">\r\n  <h3 id=\"bfiInfoTitle\"><\/h3>\r\n  <p id=\"bfiInfoText\"><\/p>\r\n  <div class=\"bfi-facts\" id=\"bfiFacts\"><\/div>\r\n  <div class=\"bfi-key\">\r\n    <span><i class=\"k-ball\" style=\"background:#34aa48\"><\/i>Chlorine<\/span>\r\n    <span><i class=\"k-ball\" style=\"background:#ececf0\"><\/i>Hydrogen<\/span>\r\n    <span><i class=\"k-ball\" style=\"background:#8c3222\"><\/i>Bromine<\/span>\r\n    <span><i class=\"k-ball\" style=\"background:#f6c426\"><\/i>Electron<\/span>\r\n  <\/div>\r\n<\/div>\r\n\r\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/bond-fission-homolytic-heterolytic.js?v=20261025p\"><\/script>\r\n<\/section>\r\n\r\n<p class=\"ols-cc-bfi-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\n\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Pick the Accurate Statement<\/h2>\n<p>Choose the accurate statement about how each bond breaks.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-134\" class=\"h5p-iframe\" data-content-id=\"134\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Free Radical Substitution Summary: Two Ways for a Bond to Break\"><\/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\">6<\/div>\n          <h2>Mechanisms and Curly Arrows<\/h2>\n        <\/div>\n\n        <p>A <strong>reaction mechanism<\/strong> is a step-by-step description of how a chemical reaction proceeds.<\/p>\n        <p>Curly arrows are used in mechanisms to show the movement of electrons. For electron-pair movement, a curly arrow must start from a <strong>lone pair of electrons<\/strong> or from the <strong>centre of a covalent bond<\/strong>.<\/p>\n        <p>Free-radical substitution uses radical chemistry, so the detailed arrow style differs from many ionic organic mechanisms. This page introduces the mechanism concept before the separate pages on initiation, propagation and termination.<\/p>\n\n        <div class=\"ols-figure-card\">\n          <div class=\"ols-figure-image\">\n            <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t4-cd-10-chloromethane-hydroxide.svg\" alt=\"Nucleophilic substitution: hydroxide lone pair attacks the \u03b4+ carbon of chloromethane, C\u2013Cl bond breaks, giving methanol and chloride\" width=\"1520\" height=\"833\">\n          <\/div>\n          <div class=\"ols-figure-caption\">\n            <p>This ionic mechanism shows electron-pair movement. Radical mechanisms use single-electron movement and are treated separately in the following subtopic pages.<\/p>\n          <\/div>\n        <\/div>\n\n        <div class=\"ols-warning-box\">\n          <p><strong>Do not mix up the arrow types:<\/strong> free-radical mechanisms involve single-electron movement, whereas many ionic mechanisms use electron-pair curly arrows.<\/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: Equation or Mechanism?<\/h2>\n<p>Decide whether an overall equation counts as a mechanism.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-726\" class=\"h5p-iframe\" data-content-id=\"726\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Free Radical Substitution True or False: An Equation Is Not a Mechanism\"><\/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: Free Radical Substitution Summary<\/h2>\n<p>Pull the whole page together by choosing the accurate statement in each round.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-1286\" class=\"h5p-iframe\" data-content-id=\"1286\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Free Radical Substitution Summary: From Unreactive Alkane to Mechanism\"><\/iframe><\/div><\/div>\n<\/section>\n\n      \n\n      <section class=\"ols-infographic-full\" aria-label=\"Free radical substitution visual summary\">\n        <h2 class=\"ols-infographic-title\">Free Radical Substitution Summary<\/h2>\n        <div class=\"ols-infographic-grid\">\n          <div class=\"ols-info-panel\">\n            <h3>1. Alkane reactivity<\/h3>\n            <p>Alkanes are usually unreactive because their C-C and C-H bonds are strong and require a large amount of energy to break.<\/p>\n          <\/div>\n          <div class=\"ols-info-panel\">\n            <h3>2. UV light starts the reaction<\/h3>\n            <p>UV light provides enough energy for homolytic fission of the halogen molecule, forming reactive halogen radicals.<\/p>\n          <\/div>\n          <div class=\"ols-info-panel\">\n            <h3>3. Chain mechanism<\/h3>\n            <p>The reaction proceeds through initiation, propagation and termination, producing substitution products and possible further substitution products.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-faq-card\" id=\"free-radical-substitution-faq\">\n        <h2>Free Radical Substitution FAQs<\/h2>\n        <p>These questions summarise the core exam points on alkane substitution and free radicals.<\/p>\n\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>Why are alkanes usually unreactive?<\/h3>\n            <p>Alkanes are usually unreactive because they contain strong C-C and C-H bonds. These bonds require a large amount of energy to break.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What condition is needed for alkanes to react with chlorine?<\/h3>\n            <p>Ultraviolet light is needed. UV light provides enough energy to break the Cl-Cl bond by homolytic fission, forming chlorine radicals.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>What is a free radical?<\/h3>\n            <p>A free radical is a species with an unpaired electron. The unpaired electron is usually represented using a dot, such as Cl\u2022.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why is the reaction called substitution?<\/h3>\n            <p>It is called substitution because a hydrogen atom in the alkane is replaced by a halogen atom.<\/p>\n          <\/div>\n\n          <div class=\"ols-faq-item\">\n            <h3>Why can a mixture of products form?<\/h3>\n            <p>After the first substitution, the halogenoalkane product can undergo further substitution. This can replace more hydrogen atoms and produce a mixture of chlorinated products.<\/p>\n          <\/div>\n        <\/div>\n      <\/section>\n\n      <!-- author card (moved to the end, 10 Oct 2026) -->\n      <div class=\"ols-author\">\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            <h2 class=\"ols-author-title\">Written by: Dr. Mohammed Al-Fatah<\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/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          <\/div>\n        <\/div>\n\n\n      <section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Continue through the alkane reaction sequence by studying each stage of the free-radical substitution mechanism.<\/p>\n\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/initiation\/\">Initiation<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/propagation\/\">Propagation<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/termination\/\">Termination<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/further-substitution\/\">Further Substitution<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/fuel\/combustion\/\">Combustion<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkenes\/electrophilic-addition-mechanism\/\">Electrophilic Addition Mechanism<\/a>\n        <\/div>\n      <\/section>\n\n      <!-- OLS Author Copyright Footprint \/ Attribution Card -->\n      <section class=\"ols-attribution-card ols-attr-std\" aria-label=\"Copyright notice\">\n<style id=\"ols-attribution-card-css\">.ols-attribution-card.ols-attr-std{background:linear-gradient(135deg,#ffffff,#f8fbff);border:1px solid rgba(28,36,75,0.14);border-radius:28px;box-shadow:0 18px 45px rgba(28,36,75,0.10);padding:34px;margin:24px 0;overflow:hidden;font-family:Poppins,Arial,sans-serif;box-sizing:border-box}.ols-attribution-card.ols-attr-std *{box-sizing:border-box}.ols-attribution-card.ols-attr-std p{margin:0;font-size:14px;line-height:1.65;font-weight:300;color:#667085}.ols-attribution-card.ols-attr-std strong{font-weight:700;color:#1C244B}@media (max-width:760px){.ols-attribution-card.ols-attr-std{padding:24px 18px;border-radius:22px}}<\/style>\n<p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n<\/section>\n\n      <script type=\"application\/ld+json\">\n      {\n        \"@context\": \"https:\/\/schema.org\",\n        \"@graph\": [\n          {\n            \"@type\": \"WebPage\",\n            \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/#webpage\",\n            \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-6-organic-chemistry-i\/alkanes\/reactions\/free-radical-substitution\/\",\n            \"name\": \"Free Radical Substitution | Edexcel A Level Chemistry Revision Notes\",\n            \"description\": \"Edexcel A Level Chemistry revision notes on free-radical substitution of alkanes with halogens, including UV light, homolytic fission, free radicals and substitution.\",\n            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