{"id":4525,"date":"2026-05-28T06:05:29","date_gmt":"2026-05-28T05:05:29","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/"},"modified":"2026-10-14T09:05:26","modified_gmt":"2026-10-14T08:05:26","slug":"trends-in-a-group","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/","title":{"rendered":"Trends in a Group"},"content":{"rendered":"\n<!--\n===============================================================================\nONLINE LEARNING SYSTEM COPYRIGHT NOTICE\n\u00a9 Online Learning System. 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\n    .ols-figure-placeholder .ols-placeholder-box { border: 2px dashed #c9973a; background: #fffaf0; border-radius: 16px; padding: 26px 22px; font-weight: 700; color: #7a4b12; text-align: center; line-height: 1.6; }\n    .ols-figure-placeholder .ols-figure-image { background: transparent; }\n    .ols-figure-placeholder { background: #ffffff; border: 1px solid rgba(28, 36, 75, 0.12); border-radius: 22px; padding: 14px; margin: 18px 0 6px; }\n    .ols-figure-placeholder .ols-figure-caption p { margin: 10px 0 0; font-size: 14px; color: #667085; text-align: center; }\n<\/style>\n\n  <div class=\"ols-revision-layout\">\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 1 Atomic Structure and The Periodic Table<\/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-1-atomic-structure-and-the-periodic-table\/atomic-structure\/\">Atomic Structure<\/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-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/\">Mass Spectrometry<\/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-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/the-mass-spectrometer\/\">The Mass Spectrometer<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/ram-calculations\/\">RAM Calculations<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/predicting-diatomic-mass-spectra\/\">Predicting Diatomic Mass Spectra<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/\">Identifying Compounds from Mass Spectra<\/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-1-atomic-structure-and-the-periodic-table\/electron-configuration\/\">Electron Configuration<\/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-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/\">Ionisation Energy<\/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-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/introduction-to-ionisation-energy\/\">Introduction to Ionisation Energy<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/successive-ionisation-energies\/\">Successive Ionisation Energies<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-period\/\">Trends in a Period<\/a>\r\n          <\/li>\r\n          <li>\r\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/\">Trends in a Group<\/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-1-atomic-structure-and-the-periodic-table\/periodic-trends\/\">Periodic Trends<\/a>\r\n      <\/li>\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-2-bonding-and-structure\/\">Bonding &amp; Structure<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-3-redox-i\/\">Redox I<\/a>\r\n      <\/li>\r\n      <li>\r\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/\">Inorganic Chemistry &amp; The Periodic Table<\/a>\r\n      <\/li>\r\n    <\/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 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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-1-atomic-structure-and-the-periodic-table\/\">Topic 1 Atomic Structure &amp; The Periodic Table<\/a> \/\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/\">Ionisation Energy<\/a> \/\n        <span>Trends in a Group<\/span>\n      <\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Trends in a Group<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to first ionisation energy trends down a group, including atomic radius, shielding, nuclear charge and why outer electrons become easier to remove.<\/p>\n\n        <div class=\"ols-badges\">\n          <div class=\"ols-badge\">Unit: Paper 1<\/div>\n          <div class=\"ols-badge\">Topic 1: Atomic Structure &amp; The Periodic Table<\/div>\n          <div class=\"ols-badge\">9CH0\/01<\/div>\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: Groups, Shells and Reactivity<\/h2>\n<p>Before you start, check what you remember about groups and the reactivity of the Group 1 metals.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"592\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">1<\/div><h2>What Does Going Down a Group Mean?<\/h2><\/div>\n        <p>A <strong>group<\/strong> is a vertical column in the periodic table. Elements in the same group have the same number of outer-shell electrons, so they often show similar chemical behaviour.<\/p>\n        <p>When you go down a group, each element has one more occupied electron shell than the element above it. This increases the distance between the nucleus and the outer electron.<\/p>\n        <div class=\"ols-key-box\">\n          <p><strong>Core idea:<\/strong> down a group, the outer electron is further from the nucleus and is shielded by more inner electron shells.<\/p>\n        <\/div>\n      <\/article>\n\n      <div class=\"ols-zoom-card\">\n        <div class=\"ols-zoom-card-image\">\n          <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/10\/t2-img-25-blocks.jpg\" alt=\"Outline periodic table shaded into s, p, d and f blocks with group numbers 1 to 18, and a panel explaining how the block is decided\" class=\"ols-zoomable-img ols-lightbox-target\" draggable=\"false\">\n        <\/div>\n        <div class=\"ols-zoom-card-caption\">\n          <p>Groups are vertical columns in the periodic table. The block also helps identify which subshell receives the outer electrons.<\/p>\n        <\/div>\n      <\/div>\n\n      <article class=\"ols-note-card\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">2<\/div><h2>Atomic Radius Increases Down a Group<\/h2><\/div>\n        <p><strong>Atomic radius increases down a group<\/strong> because each element has an additional main electron shell.<\/p>\n        <p>The outer electron is further from the nucleus, so the attraction between the nucleus and the outer electron becomes weaker. This increased distance is one of the main reasons ionisation energy decreases down a group.<\/p>\n        <div class=\"ols-key-box\">\n          <p><strong>Exam phrase:<\/strong> the outer electron is further from the nucleus because there are more occupied electron shells.<\/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: Count the Shells and Inner Electrons<\/h2>\n<p>Use the two electron arrangements to type each number.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-280\" class=\"h5p-iframe\" data-content-id=\"280\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Trends in a Group Fill in the Blanks: Shells and Inner Electrons\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <div class=\"ols-figure-card\">\n<div class=\"ols-figure-image\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/fix-7.jpg\" alt=\"Metallic radius down Group 2 (Be 112, Mg 160, Ca 197, Sr 215, Ba 222 pm) as circles drawn to scale, with the reason: one more electron shell, more shielding, outweighing the extra nuclear charge\"><\/div>\n<div class=\"ols-figure-caption\"><p>Each element lower in Group 2 has an extra occupied electron shell, so its outer electron is further from the nucleus.<\/p><\/div>\n<\/div>\n\n      <article class=\"ols-note-card purple\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">3<\/div><h2>Shielding Increases Down a Group<\/h2><\/div>\n        <p>As atoms get larger down a group, there are more inner shells between the nucleus and the outer electron. These inner shells <strong>shield<\/strong> the outer electron from the full attraction of the nucleus.<\/p>\n        <p>This means the outer electron experiences a lower effective nuclear attraction, even though the total number of protons in the nucleus has increased.<\/p>\n        <div class=\"ols-definition-box\">\n          <p><strong>Shielding:<\/strong> the reduction in attraction between the nucleus and an outer electron due to repulsion from inner-shell electrons.<\/p>\n        <\/div>\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Factor down a group<\/th>\n                <th>What happens?<\/th>\n                <th>Effect on the outer electron<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Factor down a group\">Number of shells<\/td>\n                <td data-label=\"What happens?\">Increases<\/td>\n                <td data-label=\"Effect on the outer electron\">Outer electron is further from the nucleus.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Factor down a group\">Shielding<\/td>\n                <td data-label=\"What happens?\">Increases<\/td>\n                <td data-label=\"Effect on the outer electron\">Inner shells reduce the attraction felt by the outer electron.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Factor down a group\">Nuclear charge<\/td>\n                <td data-label=\"What happens?\">Increases<\/td>\n                <td data-label=\"Effect on the outer electron\">More protons increase attraction, but this is outweighed by extra shells and shielding.<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Factor down a group\">First ionisation energy<\/td>\n                <td data-label=\"What happens?\">Decreases<\/td>\n                <td data-label=\"Effect on the outer electron\">Less energy is needed to remove the outer electron.<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n      <\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Quick Check: Rank the Noble Gases<\/h2>\n<p>Drag the noble gases into order of first ionisation energy, highest at the top.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-279\" class=\"h5p-iframe\" data-content-id=\"279\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Trends in a Group Sort: Noble Gases by First Ionisation Energy\"><\/iframe><\/div><\/div>\n<\/section>\n\n      <article class=\"ols-note-card orange\">\n        <div class=\"ols-note-title\"><div class=\"ols-note-icon\">4<\/div><h2>First Ionisation Energy Decreases Down a Group<\/h2><\/div>\n        <p>First ionisation energy generally <strong>decreases down a group<\/strong>. This means it becomes easier to remove the outer electron from atoms lower in the group.<\/p>\n        <p>The nuclear charge does increase because atoms lower in the group have more protons. However, the effect of the extra shells and increased shielding is greater. The outer electron is less strongly attracted to the nucleus, so less energy is needed to remove it.<\/p>\n        <p>The values for Group 2 show the size of the decrease:<\/p>\n        <div class=\"ols-table-wrap\">\n          <table class=\"ols-table\">\n            <thead>\n              <tr>\n                <th>Element<\/th>\n                <th>Protons<\/th>\n                <th>Inner-shell electrons<\/th>\n                <th>First ionisation energy \/ kJ mol\u207b\u00b9<\/th>\n              <\/tr>\n            <\/thead>\n            <tbody>\n              <tr>\n                <td data-label=\"Element\">Be (2,2)<\/td>\n                <td data-label=\"Protons\">4<\/td>\n                <td data-label=\"Inner-shell electrons\">2<\/td>\n                <td data-label=\"First ionisation energy \/ kJ mol\u207b\u00b9\">900<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Element\">Mg (2,8,2)<\/td>\n                <td data-label=\"Protons\">12<\/td>\n                <td data-label=\"Inner-shell electrons\">10<\/td>\n                <td data-label=\"First ionisation energy \/ kJ mol\u207b\u00b9\">738<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Element\">Ca (2,8,8,2)<\/td>\n                <td data-label=\"Protons\">20<\/td>\n                <td data-label=\"Inner-shell electrons\">18<\/td>\n                <td data-label=\"First ionisation energy \/ kJ mol\u207b\u00b9\">590<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Element\">Sr (2,8,18,8,2)<\/td>\n                <td data-label=\"Protons\">38<\/td>\n                <td data-label=\"Inner-shell electrons\">36<\/td>\n                <td data-label=\"First ionisation energy \/ kJ mol\u207b\u00b9\">550<\/td>\n              <\/tr>\n              <tr>\n                <td data-label=\"Element\">Ba (2,8,18,18,8,2)<\/td>\n                <td data-label=\"Protons\">56<\/td>\n                <td data-label=\"Inner-shell electrons\">54<\/td>\n                <td data-label=\"First ionisation energy \/ kJ mol\u207b\u00b9\">503<\/td>\n              <\/tr>\n            <\/tbody>\n          <\/table>\n        <\/div>\n        <p>From one element to the next, the number of protons and the number of inner-shell electrons rise by the same amount. The extra nuclear charge is cancelled by the extra shielding, so the greater distance from the nucleus decides the trend.<\/p>\n        <div class=\"ols-key-box\">\n          <p><strong>Best exam answer:<\/strong> down a group, there are more occupied shells, the outer electron is further from the nucleus and shielding increases. These effects outweigh the increased nuclear charge.<\/p>\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\/10\/t2-img-26-iegroup.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\/10\/t2-img-26-iegroup.jpg\" alt=\"Bar chart of first ionisation energy down Group 2 from beryllium 900 to barium 503 kJ mol\u207b\u00b9, with shell diagrams of Be, Mg and Ca\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Down Group 2 each atom has one more shell, so the outer electron is further away and easier to remove.<\/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: Explain Chlorine and Bromine<\/h2>\n<p>Write a short explanation, then compare it with the mark points and the model answer.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-281\" class=\"h5p-iframe\" data-content-id=\"281\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Trends in a Group Explain: Chlorine Compared with Bromine\"><\/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: Pick the Accurate Statement<\/h2>\n<p>In each round, choose the one statement that is accurate.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-275\" class=\"h5p-iframe\" data-content-id=\"275\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Trends in a Group Summary: Size, Shielding and Nuclear Charge\"><\/iframe><\/div><\/div>\n<\/section>\n\n      \n\n      <section class=\"ols-quicksnap-card\">\n        <h2>QuickSnap<\/h2>\n        <p>This text summary condenses the page into the essential exam ideas.<\/p>\n        <ul class=\"ols-quicksnap-list\">\n          <li><strong>Down a group, atomic radius increases<\/strong> because each element has an additional occupied electron shell.<\/li>\n          <li><strong>The outer electron is further from the nucleus<\/strong>, so the attraction between the nucleus and the outer electron is weaker.<\/li>\n          <li><strong>Shielding increases<\/strong> because there are more inner shells between the nucleus and the outer electron.<\/li>\n          <li><strong>Nuclear charge increases<\/strong>, but the effect of extra shells and shielding outweighs this.<\/li>\n          <li><strong>First ionisation energy decreases<\/strong>, so less energy is needed to remove the outer electron.<\/li>\n          <li><strong>Group 2 data:<\/strong> Be 900, Mg 738, Ca 590, Sr 550, Ba 503 kJ mol\u207b\u00b9.<\/li>\n          <li><strong>Best exam answers<\/strong> explicitly use distance from the nucleus, shielding, nuclear charge and attraction.<\/li>\n        <\/ul>\n      <\/section>\n\n\n\n      <section class=\"ols-faq-card\">\n        <h2>FAQs<\/h2>\n        <p>These questions target the most common exam wording for ionisation energy trends down a group.<\/p>\n        <div class=\"ols-faq-list\">\n          <div class=\"ols-faq-item\">\n            <h3>Why does first ionisation energy decrease down a group?<\/h3>\n            <p>First ionisation energy decreases down a group because atoms have more occupied electron shells. The outer electron is further from the nucleus and is shielded more strongly by inner shells, so the attraction to the nucleus is weaker.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why does atomic radius increase down a group?<\/h3>\n            <p>Atomic radius increases down a group because each element has an additional main electron shell. This places the outer electron further from the nucleus.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>What is shielding in ionisation energy?<\/h3>\n            <p>Shielding is the reduction in attraction between the nucleus and the outer electron due to repulsion from inner-shell electrons. More inner shells mean greater shielding.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>Why does increased nuclear charge not make ionisation energy increase down a group?<\/h3>\n            <p>Nuclear charge increases down a group because there are more protons. However, the extra occupied shells and increased shielding have a greater effect, so the outer electron is less strongly attracted overall.<\/p>\n          <\/div>\n          <div class=\"ols-faq-item\">\n            <h3>What wording should I use in an exam answer?<\/h3>\n            <p>Use this sequence: more occupied shells, larger atomic radius, more shielding, weaker attraction between the nucleus and the outer electron, less energy needed to remove the electron.<\/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\" class=\"ols-author-avatar-img\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\" alt=\"Dr. Mohammed Al-Fatah\">\n          <div class=\"ols-author-content\">\n            <h2 class=\"ols-author-title\">Written by:<br><span>Dr. Mohammed Al-Fatah<\/span><\/h2>\n            <p class=\"ols-author-description\">Chemistry specialist revision notes for A Level Chemistry.<\/p>\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\"><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\"><\/path><\/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>Build the surrounding knowledge needed for ionisation energy, electron configuration and periodic trends.<\/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\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/introduction-to-ionisation-energy\/\">Introduction to Ionisation Energy<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/successive-ionisation-energies\/\">Successive Ionisation Energies<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-period\/\">Trends in a Period<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/electron-configuration\/\">Electron Configuration<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/mass-spectrometry\/\">Mass Spectrometry<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-2-bonding-and-structure\/\">Bonding &amp; Structure<\/a>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-attribution-card ols-attr-std\" aria-label=\"Copyright notice\">\n<style id=\"ols-attribution-card-css\">.ols-attribution-card.ols-attr-std{background:linear-gradient(135deg,#ffffff,#f8fbff);border:1px solid rgba(28,36,75,0.14);border-radius:28px;box-shadow:0 18px 45px rgba(28,36,75,0.10);padding:34px;margin:24px 0;overflow:hidden;font-family:Poppins,Arial,sans-serif;box-sizing:border-box}.ols-attribution-card.ols-attr-std *{box-sizing:border-box}.ols-attribution-card.ols-attr-std p{margin:0;font-size:14px;line-height:1.65;font-weight:300;color:#667085}.ols-attribution-card.ols-attr-std strong{font-weight:700;color:#1C244B}@media (max-width:760px){.ols-attribution-card.ols-attr-std{padding:24px 18px;border-radius:22px}}<\/style>\n<p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. It may not be copied, reproduced, redistributed or adapted without written permission.<\/p>\n<\/section>\n\n      <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-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/\",\n                        \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/\",\n                        \"name\": \"Trends in a Group - Edexcel A Level Chemistry Revision Notes\",\n                        \"description\": \"Edexcel A Level Chemistry revision notes on ionisation energy trends down a group, including atomic radius, shielding, nuclear charge and exam wording.\",\n                        \"inLanguage\": \"en-GB\",\n                        \"isPartOf\": {\n                                \"@type\": \"WebSite\",\n                                \"name\": \"Online Learning System\",\n                                \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/\"\n                        },\n                        \"author\": {\n                                \"@type\": \"Person\",\n                                \"name\": \"Dr. Mohammed Al-Fatah\",\n                                \"url\": \"https:\/\/www.linkedin.com\/in\/doctormohammedfatah\/\"\n                        },\n                        \"publisher\": {\n                                \"@type\": \"Organization\",\n                                \"name\": \"Online Learning System\",\n                                \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/\"\n                        },\n                        \"about\": [\n                                { \"@type\": \"Thing\", \"name\": \"Ionisation energy\" },\n                                { \"@type\": \"Thing\", \"name\": \"Periodic trends\" },\n                                { \"@type\": \"Thing\", \"name\": \"Atomic radius\" },\n                                { \"@type\": \"Thing\", \"name\": \"Shielding\" }\n                        ]\n                },\n                {\n                        \"@type\": \"BreadcrumbList\",\n                        \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/#breadcrumb\",\n                        \"itemListElement\": [\n                                { \"@type\": \"ListItem\", \"position\": 1, \"name\": \"Revision Notes\", \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/\" },\n                                { \"@type\": \"ListItem\", \"position\": 2, \"name\": \"A Level Chemistry\", \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/\" },\n                                { \"@type\": \"ListItem\", \"position\": 3, \"name\": \"Edexcel\", \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/\" },\n                                { \"@type\": \"ListItem\", \"position\": 4, \"name\": \"Topic 1 Atomic Structure & The Periodic Table\", \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/\" },\n                                { \"@type\": \"ListItem\", \"position\": 5, \"name\": \"Ionisation Energy\", \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/\" },\n                                { \"@type\": \"ListItem\", \"position\": 6, \"name\": \"Trends in a Group\", \"item\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/\" }\n                        ]\n                },\n                {\n                        \"@type\": \"Course\",\n                        \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/#course\",\n                        \"name\": \"Trends in a Group - Ionisation Energy\",\n                        \"description\": \"Free Edexcel A Level Chemistry revision notes explaining why first ionisation energy decreases down a group using atomic radius, shielding and nuclear attraction.\",\n                        \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/\",\n                        \"provider\": {\n                                \"@type\": \"Organization\",\n                                \"name\": \"Online Learning System\",\n                                \"sameAs\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/\"\n                        },\n                        \"educationalLevel\": \"A Level Chemistry\",\n                        \"teaches\": [\n                                \"Ionisation energy trends down a group\",\n                                \"Atomic radius down a group\",\n                                \"Shielding and nuclear attraction\",\n                                \"Exam wording for periodic trends\"\n                        ]\n                },\n                {\n                        \"@type\": \"FAQPage\",\n                        \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/#faq\",\n                        \"mainEntity\": [\n                                {\n                                        \"@type\": \"Question\",\n                                        \"name\": \"Why does first ionisation energy decrease down a group?\",\n                                        \"acceptedAnswer\": {\n                                                \"@type\": \"Answer\",\n                                                \"text\": \"First ionisation energy decreases down a group because atoms have more occupied electron shells. The outer electron is further from the nucleus and is shielded more strongly by inner shells, so the attraction to the nucleus is weaker.\"\n                                        }\n                                },\n                                {\n                                        \"@type\": \"Question\",\n                                        \"name\": \"Why does atomic radius increase down a group?\",\n                                        \"acceptedAnswer\": {\n                                                \"@type\": \"Answer\",\n                                                \"text\": \"Atomic radius increases down a group because each element has an additional main electron shell. 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                       \"@id\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/trends-in-a-group\/#relatedtopics\",\n                        \"name\": \"Related Ionisation Energy Revision Notes\",\n                        \"itemListElement\": [\n                                {\n                                        \"@type\": \"ListItem\",\n                                        \"position\": 1,\n                                        \"item\": {\n                                                \"@type\": \"Course\",\n                                                \"name\": \"Introduction to Ionisation Energy\",\n                                                \"url\": \"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-1-atomic-structure-and-the-periodic-table\/ionisation-energy\/introduction-to-ionisation-energy\/\",\n     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