{"id":7900,"date":"2026-09-14T21:37:04","date_gmt":"2026-09-14T20:37:04","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/"},"modified":"2026-09-14T21:41:31","modified_gmt":"2026-09-14T20:41:31","slug":"2-1-1-atomic-structure-and-isotopes","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/","title":{"rendered":"2.1.1 Atomic Structure and Isotopes"},"content":{"rendered":"\n<div class=\"ols-ocr211-page\">\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>OCR A Level Chemistry A<\/p>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>2.1.1 Atomic Structure and Isotopes<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/\">Section overview<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/atomic-structure\/\">Atomic Structure<\/a><\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/mass-spectrometry\/\">Mass Spectrometry<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/mass-spectrometry\/the-mass-spectrometer\/\">The Mass Spectrometer<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/mass-spectrometry\/ram-calculations\/\">RAM Calculations<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/mass-spectrometry\/predicting-diatomic-mass-spectra\/\">Predicting Diatomic Mass Spectra<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/mass-spectrometry\/identifying-compounds-from-mass-spectra\/\">Identifying Compounds from Mass Spectra<\/a><\/li>\n        <\/ul>\n      <\/li>\n    <\/ul>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>Other OCR Sections<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-2-1-electron-structure\/\">2.2.1 Electron Structure<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-2-2-bonding-and-structure\/\">2.2.2 Bonding and Structure<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/3-1-1-periodicity\/\">3.1.1 Periodicity<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/4-1-1-basic-concepts-of-organic-chemistry\/\">4.1.1 Basic Concepts of Organic Chemistry<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/4-1-2-alkanes\/\">4.1.2 Alkanes<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/4-1-3-alkenes\/\">4.1.3 Alkenes<\/a><\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\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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column; }\n      .ols-ocr211-spec-code { flex: 0 0 auto; min-height: 34px; }\n    }\n  <\/style>\n\n  <!-- BREADCRUMB BAR -->\n  <div class=\"ols-ocr211-breadcrumb-bar\">\n    <div class=\"ols-ocr211-container\">\n      <nav class=\"ols-ocr211-breadcrumb\" 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\/ocr-a\/\">OCR<\/a> \/\n        <span>2.1.1 Atomic Structure and Isotopes<\/span>\n      <\/nav>\n    <\/div>\n  <\/div>\n\n  <!-- INTRO -->\n  <section class=\"ols-ocr211-intro\">\n    <div class=\"ols-ocr211-container\">\n      <div class=\"ols-ocr211-intro-inner\">\n        <div>\n          <div class=\"ols-ocr211-eyebrow\">OCR A Level Chemistry A &#8211; Module 2 Foundations in Chemistry<\/div>\n          <h1>2.1.1<br>Atomic Structure and Isotopes<\/h1>\n          <div class=\"ols-ocr211-accent-bar\"><\/div>\n          <p class=\"ols-ocr211-intro-lead\">Section 2.1.1 covers the structure of the atom, isotopes, relative isotopic, atomic, molecular and formula mass, and how mass spectrometry gives relative isotopic masses and abundances. These pages cover atomic structure and isotopes and the four mass spectrometry pages; relative molecular and formula mass are used throughout 2.1.3 Amount of Substance.<\/p>\n        <\/div>\n        <div class=\"ols-ocr211-info-grid\">\n          <div class=\"ols-ocr211-info-card\"><div class=\"ols-ocr211-info-card-label\">Exam Paper<\/div><div class=\"ols-ocr211-info-card-value\">Paper 1 &amp; 2<\/div><div class=\"ols-ocr211-info-card-sub\">H432\/01 and H432\/02<\/div><\/div>\n          <div class=\"ols-ocr211-info-card\"><div class=\"ols-ocr211-info-card-label\">Specification Points<\/div><div class=\"ols-ocr211-info-card-value\">2.1.1 (a) &#8211; (e)<\/div><div class=\"ols-ocr211-info-card-sub\">5 learning outcomes<\/div><\/div>\n          <div class=\"ols-ocr211-info-card\"><div class=\"ols-ocr211-info-card-label\">Topic Parts<\/div><div class=\"ols-ocr211-info-card-value\">2 of 2 live<\/div><div class=\"ols-ocr211-info-card-sub\">Atomic Structure, Mass Spectrometry<\/div><\/div>\n          <div class=\"ols-ocr211-info-card\"><div class=\"ols-ocr211-info-card-label\">Exam Board<\/div><div class=\"ols-ocr211-info-card-value\">OCR A<\/div><div class=\"ols-ocr211-info-card-sub\">H432 (2015 onwards)<\/div><\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n\n  <!-- TOPIC CARDS -->\n  <section class=\"ols-ocr211-topics\">\n    <div class=\"ols-ocr211-container\">\n      <div class=\"ols-ocr211-section-header\">\n        <h2 class=\"ols-ocr211-section-title\">Revision Notes<\/h2>\n        <p class=\"ols-ocr211-section-sub\">Work through 2.1.1 in a structured sequence.<\/p>\n      <\/div>\n      <div class=\"ols-ocr211-cards-grid\">\n        <!-- Card 1: Atomic Structure -->\n        <a class=\"ols-ocr211-card ols-ocr211-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/atomic-structure\/\">\n          <div class=\"ols-ocr211-card-img-wrap\">\n            <div class=\"ols-ocr211-visual ols-ocr211-visual--ionic\">\n              <div class=\"ols-ocr211-visual-panel\">\n                <div class=\"ols-ocr211-visual-kicker\">Particles<\/div>\n                <div class=\"ols-ocr211-visual-main\">Atomic<br>Structure<\/div>\n                <div class=\"ols-ocr211-config-line\" aria-hidden=\"true\"><span>p\u207a n\u2070 e\u207b<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr211-card-num\">1<\/div>\n          <\/div>\n          <div class=\"ols-ocr211-card-body\">\n            <p class=\"ols-ocr211-card-title\">Atomic Structure<\/p>\n            <p class=\"ols-ocr211-card-desc\">Protons, neutrons and electrons, atomic and mass number, isotopes and working out particle numbers in atoms and ions (2.1.1 (a), (b)).<\/p>\n            <span class=\"ols-ocr211-card-cta\">Start revising<svg viewBox=\"0 0 16 16\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M3 8h10M9 4l4 4-4 4\"><\/path><\/svg><\/span>\n          <\/div>\n        <\/a>\n        <!-- Card 2: Mass Spectrometry -->\n        <a class=\"ols-ocr211-card ols-ocr211-card--available\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/mass-spectrometry\/\">\n          <div class=\"ols-ocr211-card-img-wrap\">\n            <div class=\"ols-ocr211-visual ols-ocr211-visual--forces\">\n              <div class=\"ols-ocr211-visual-panel\">\n                <div class=\"ols-ocr211-visual-kicker\">Instrument<\/div>\n                <div class=\"ols-ocr211-visual-main\">Mass<br>Spectrometry<\/div>\n                <div class=\"ols-ocr211-config-line\" aria-hidden=\"true\"><span>m\/z<\/span><\/div>\n              <\/div>\n            <\/div>\n            <div class=\"ols-ocr211-card-num\">2<\/div>\n          <\/div>\n          <div class=\"ols-ocr211-card-body\">\n            <p class=\"ols-ocr211-card-title\">Mass Spectrometry<\/p>\n            <p class=\"ols-ocr211-card-desc\">How the mass spectrometer works, relative isotopic and atomic mass, RAM from abundances, diatomic spectra and identifying compounds (2.1.1 (c), (d)).<\/p>\n            <span class=\"ols-ocr211-card-cta\">Start revising<svg viewBox=\"0 0 16 16\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" stroke-linecap=\"round\" stroke-linejoin=\"round\"><path d=\"M3 8h10M9 4l4 4-4 4\"><\/path><\/svg><\/span>\n          <\/div>\n        <\/a>\n      <\/div>\n    <\/div>\n  <\/section>\n  <!-- SPECIFICATION -->\n  <section class=\"ols-ocr211-spec-section\">\n    <div class=\"ols-ocr211-container\">\n      <div class=\"ols-ocr211-spec-wrap\">\n        <div class=\"ols-ocr211-spec-pill\">Specification Coverage<\/div>\n        <h2 class=\"ols-ocr211-spec-heading\">2.1.1 Atomic Structure and Isotopes &#8211; OCR A Level Chemistry A<\/h2>\n        <p class=\"ols-ocr211-spec-intro-text\">The following OCR A learning outcomes state what candidates should be able to do. Wording is taken from the OCR A Level Chemistry A (H432) specification.<\/p>\n        <h3 class=\"ols-ocr211-spec-group-title\">2.1.1 Atomic Structure and Isotopes<\/h3>\n        <div class=\"ols-ocr211-spec-rows\">\n          <div class=\"ols-ocr211-spec-row ols-ocr211-spec-row--light\">\n<div class=\"ols-ocr211-spec-code\">2.1.1(a)<\/div>\n<div class=\"ols-ocr211-spec-text\"><strong>Isotopes<\/strong><div class=\"ols-ocr211-spec-sub-list\"><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">i<\/div><div class=\"ols-ocr211-spec-sub-text\">isotopes as atoms of the same element with different numbers of neutrons<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">ii<\/div><div class=\"ols-ocr211-spec-sub-text\">isotopes as atoms of the same element with different masses<\/div><\/div><\/div><\/div>\n<\/div>\n          <div class=\"ols-ocr211-spec-row ols-ocr211-spec-row--mid\">\n<div class=\"ols-ocr211-spec-code ols-ocr211-spec-code--mid\">2.1.1(b)<\/div>\n<div class=\"ols-ocr211-spec-text\"><strong>Atomic structure of atoms and ions<\/strong><div class=\"ols-ocr211-spec-sub-list\"><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">i<\/div><div class=\"ols-ocr211-spec-sub-text\">atomic structure in terms of the number of protons for atoms, given the atomic number and mass number<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">ii<\/div><div class=\"ols-ocr211-spec-sub-text\">atomic structure in terms of the number of neutrons for atoms, given the atomic number and mass number<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">iii<\/div><div class=\"ols-ocr211-spec-sub-text\">atomic structure in terms of the number of electrons for atoms, given the atomic number and mass number<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">iv<\/div><div class=\"ols-ocr211-spec-sub-text\">atomic structure in terms of the number of protons for ions, given the atomic number, mass number and ionic charge<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">v<\/div><div class=\"ols-ocr211-spec-sub-text\">atomic structure in terms of the number of neutrons for ions, given the atomic number, mass number and ionic charge<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">vi<\/div><div class=\"ols-ocr211-spec-sub-text\">atomic structure in terms of the number of electrons for ions, given the atomic number, mass number and ionic charge<\/div><\/div><\/div><\/div>\n<\/div>\n          <div class=\"ols-ocr211-spec-row ols-ocr211-spec-row--light\">\n<div class=\"ols-ocr211-spec-code\">2.1.1(c)<\/div>\n<div class=\"ols-ocr211-spec-text\"><strong>Relative isotopic and relative atomic mass<\/strong><div class=\"ols-ocr211-spec-sub-list\"><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">i<\/div><div class=\"ols-ocr211-spec-sub-text\">explanation of the term relative isotopic mass (mass compared with 1\/12th mass of carbon-12), based on the mass of a 12C atom, the standard for atomic masses<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">ii<\/div><div class=\"ols-ocr211-spec-sub-text\">explanation of the term relative atomic mass (weighted mean mass compared with 1\/12th mass of carbon-12), based on the mass of a 12C atom, the standard for atomic masses<\/div><\/div><\/div><\/div>\n<\/div>\n          <div class=\"ols-ocr211-spec-row ols-ocr211-spec-row--mid\">\n<div class=\"ols-ocr211-spec-code ols-ocr211-spec-code--mid\">2.1.1(d)<\/div>\n<div class=\"ols-ocr211-spec-text\"><strong>Mass spectrometry<\/strong><div class=\"ols-ocr211-spec-sub-list\"><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">i)-a<\/div><div class=\"ols-ocr211-spec-sub-text\">use of mass spectrometry in the determination of relative isotopic masses<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">i)-b<\/div><div class=\"ols-ocr211-spec-sub-text\">use of mass spectrometry in the determination of relative abundances of the isotopes<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">ii<\/div><div class=\"ols-ocr211-spec-sub-text\">use of mass spectrometry in the calculation of the relative atomic mass of an element from the relative abundances of its isotopes<\/div><\/div><\/div><\/div>\n<\/div>\n          <div class=\"ols-ocr211-spec-row ols-ocr211-spec-row--light\">\n<div class=\"ols-ocr211-spec-code\">2.1.1(e)<\/div>\n<div class=\"ols-ocr211-spec-text\"><strong>Relative molecular and formula mass<\/strong><div class=\"ols-ocr211-spec-sub-list\"><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">i<\/div><div class=\"ols-ocr211-spec-sub-text\">use of the term relative molecular mass, Mr<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">ii<\/div><div class=\"ols-ocr211-spec-sub-text\">use of the term relative formula mass<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">iii<\/div><div class=\"ols-ocr211-spec-sub-text\">calculation of relative molecular mass from relative atomic masses<\/div><\/div><div class=\"ols-ocr211-spec-sub-row\"><div class=\"ols-ocr211-spec-sub-code\">iv<\/div><div class=\"ols-ocr211-spec-sub-text\">calculation of relative formula mass from relative atomic masses<\/div><\/div><\/div><\/div>\n<\/div>\n        <\/div>\n      <\/div>\n    <\/div>\n  <\/section>\n  <script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@graph\": [\n    {\n      \"@type\": \"WebPage\",\n      \"@id\": 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