{"id":8099,"date":"2026-09-15T08:35:07","date_gmt":"2026-09-15T07:35:07","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/ions-and-ionic-formulae\/"},"modified":"2026-09-22T10:07:48","modified_gmt":"2026-09-22T09:07:48","slug":"ions-and-ionic-formulae","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/ions-and-ionic-formulae\/","title":{"rendered":"Ions and Ionic Formulae"},"content":{"rendered":"\n<!--\n===============================================================================\nONLINE LEARNING SYSTEM COPYRIGHT NOTICE\n\u00a9 Online Learning System. 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background: #2563eb !important;\n      color: #ffffff !important;\n    }\n\n    body.ols-lightbox-lock {\n      overflow: hidden !important;\n    }\n\n    @media (max-width: 760px) {\n      .ols-zoom-card {\n        border-radius: 22px !important;\n        overflow: hidden !important;\n      }\n\n      .ols-zoom-card-image {\n        min-height: auto !important;\n        padding: 12px !important;\n        overflow: hidden !important;\n        border-top-left-radius: 22px !important;\n        border-top-right-radius: 22px !important;\n      }\n\n      .ols-zoom-card img.ols-zoomable-img,\n      .ols-zoom-card img.ols-zoomable-img:hover {\n        transform: none !important;\n        box-shadow: none !important;\n      }\n\n      .ols-zoom-card-caption {\n        border-bottom-left-radius: 22px !important;\n        border-bottom-right-radius: 22px !important;\n      }\n\n      .ols-image-lightbox {\n        padding: 14px !important;\n      }\n\n      .ols-image-lightbox-img {\n        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<p>OCR A Level Chemistry A<\/p>\n  <\/div>\n  <div class=\"ols-topic-group\">\n    <h4>2.1.2 Compounds, Formulae and Equations<\/h4>\n    <ul class=\"ols-topic-list\">\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/\">Section overview<\/a><\/li>\n<li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/ions-and-ionic-formulae\/\">Ions and Ionic Formulae<\/a><\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/equations-and-reaction-types\/\">Equations and Reaction Types<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/equations-and-reaction-types\/writing-chemical-equations\/\">Writing Chemical Equations<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/equations-and-reaction-types\/ionic-and-full-equations\/\">Ionic and Full Equations<\/a><\/li>\n          <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-4-acids\/typical-reactions-of-acids\/\">Typical Reactions of Acids<\/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\/2-1-1-atomic-structure-and-isotopes\/\">2.1.1 Atomic Structure and Isotopes<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-3-amount-of-substance\/\">2.1.3 Amount of Substance<\/a><\/li>\n      <li><a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-4-acids\/\">2.1.4 Acids<\/a><\/li>\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 = 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\/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/\">2.1.2 Compounds, Formulae and Equations<\/a> \/\n<span>Ions and Ionic Formulae<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Ions and Ionic Formulae<\/h1>\n        <p class=\"ols-page-intro\">A concise OCR A Level Chemistry A revision guide to predicting the charge on a simple ion from its group, the formulae of the nitrate, carbonate, sulfate, hydroxide, ammonium, zinc and silver ions, and constructing the formula of any ionic compound by balancing charges (2.1.2(a)).<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Paper 1 and 2<\/div>\n<div class=\"ols-badge\">2.1.2 Compounds, Formulae and Equations<\/div>\n<div class=\"ols-badge\">H432\/01 and H432\/02<\/div>\n<\/div>\n\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      <\/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: Losing and Gaining Electrons<\/h2>\n<p>Before you start, check the GCSE picture of how ions are formed.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"807\"><\/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>Predicting the Charge on a Simple Ion<\/h2>\n<\/div>\n<p>A metal atom in Groups 1, 2 or 13 loses its outer electrons to reach the electron configuration of the previous noble gas; a non-metal atom in Groups 15, 16 or 17 gains electrons to reach the next. The number of electrons lost or gained is the <strong>charge on the ion<\/strong>, and it can be read straight from the group number.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Group<\/th><th>Electrons lost or gained<\/th><th>Ion charge<\/th><th>Examples<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>1<\/strong><\/td><td>Lose 1<\/td><td>1+<\/td><td>Li<sup>+<\/sup>, Na<sup>+<\/sup>, K<sup>+<\/sup><\/td><\/tr>\n<tr><td><strong>2<\/strong><\/td><td>Lose 2<\/td><td>2+<\/td><td>Mg<sup>2+<\/sup>, Ca<sup>2+<\/sup>, Ba<sup>2+<\/sup><\/td><\/tr>\n<tr><td><strong>3<\/strong><\/td><td>Lose 3<\/td><td>3+<\/td><td>Al<sup>3+<\/sup><\/td><\/tr>\n<tr><td><strong>5<\/strong><\/td><td>Gain 3<\/td><td>3-<\/td><td>N<sup>3-<\/sup>, P<sup>3-<\/sup><\/td><\/tr>\n<tr><td><strong>6<\/strong><\/td><td>Gain 2<\/td><td>2-<\/td><td>O<sup>2-<\/sup>, S<sup>2-<\/sup><\/td><\/tr>\n<tr><td><strong>7<\/strong><\/td><td>Gain 1<\/td><td>1-<\/td><td>F<sup>&#8211;<\/sup>, Cl<sup>&#8211;<\/sup>, Br<sup>&#8211;<\/sup>, I<sup>&#8211;<\/sup><\/td><\/tr>\n<tr><td><strong>Transition metals<\/strong><\/td><td>Variable<\/td><td>Given in the name<\/td><td>Fe<sup>2+<\/sup> in iron(II), Fe<sup>3+<\/sup> in iron(III)<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Metals form positive ions with the charge equal to the group number; non-metals form negative ions with the charge equal to 8 minus the group number.<\/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: Charges from a Neighbour<\/h2>\n<p>Five rapid questions; each one names an element in the same group to work from.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-469\" class=\"h5p-iframe\" data-content-id=\"469\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Ionic Formulae Quick Fire: Charges from a Neighbour in the Same Group\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>The Compound Ions You Must Know<\/h2>\n<\/div>\n<p>Some ions are groups of atoms covalently bonded together that carry an overall charge. OCR names five that you must be able to write from memory.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Ion<\/th><th>Formula<\/th><th>Charge<\/th><th>Typical compound<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Sulfate<\/strong><\/td><td>SO<sub>4<\/sub><sup>2-<\/sup><\/td><td>2-<\/td><td>MgSO<sub>4<\/sub><\/td><\/tr>\n<tr><td><strong>Hydroxide<\/strong><\/td><td>OH<sup>&#8211;<\/sup><\/td><td>1-<\/td><td>Ca(OH)<sub>2<\/sub><\/td><\/tr>\n<tr><td><strong>Nitrate<\/strong><\/td><td>NO<sub>3<\/sub><sup>&#8211;<\/sup><\/td><td>1-<\/td><td>KNO<sub>3<\/sub><\/td><\/tr>\n<tr><td><strong>Carbonate<\/strong><\/td><td>CO<sub>3<\/sub><sup>2-<\/sup><\/td><td>2-<\/td><td>Na<sub>2<\/sub>CO<sub>3<\/sub><\/td><\/tr>\n<tr><td><strong>Ammonium<\/strong><\/td><td>NH<sub>4<\/sub><sup>+<\/sup><\/td><td>1+<\/td><td>NH<sub>4<\/sub>Cl<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<div class=\"ols-zoom-card\">\n<div class=\"ols-zoom-card-image\">\n<a class=\"ols-lightbox-link\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/common-compound-ions-structures-and-charges.jpg\" aria-label=\"Open image full screen\">\n<img decoding=\"async\" class=\"ols-zoomable-img ols-lightbox-target\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/09\/common-compound-ions-structures-and-charges.jpg\" alt=\"Reference card of the common compound ions: sulfate, hydroxide, nitrate, carbonate and ammonium, each with its structure and charge\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>The five compound ions OCR expects you to recall.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Ammonium is the only common positive compound ion. Sulfate and carbonate are 2-; hydroxide and nitrate are 1-.<\/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: Inside a Compound Ion<\/h2>\n<p>Decide whether the statement about ammonium nitrate is true or false.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-808\" class=\"h5p-iframe\" data-content-id=\"808\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Ionic Formulae True or False: Two Nitrogens in Ammonium Nitrate\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">3<\/div>\n<h2>Constructing the Formula of an Ionic Compound<\/h2>\n<\/div>\n<p>An ionic compound is neutral overall, so the positive and negative charges must cancel. Use the <strong>charge-balance method<\/strong>: write the ions, find the lowest number of each that makes the total charge zero, and write the formula with those numbers as subscripts. Brackets go round a compound ion when more than one is needed.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Compound<\/th><th>Ions<\/th><th>Balance the charges<\/th><th>Formula<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Magnesium chloride<\/strong><\/td><td>Mg<sup>2+<\/sup>, Cl<sup>&#8211;<\/sup><\/td><td>One 2+ needs two 1-<\/td><td>MgCl<sub>2<\/sub><\/td><\/tr>\n<tr><td><strong>Aluminium oxide<\/strong><\/td><td>Al<sup>3+<\/sup>, O<sup>2-<\/sup><\/td><td>Two 3+ (6+) balance three 2- (6-)<\/td><td>Al<sub>2<\/sub>O<sub>3<\/sub><\/td><\/tr>\n<tr><td><strong>Calcium nitrate<\/strong><\/td><td>Ca<sup>2+<\/sup>, NO<sub>3<\/sub><sup>&#8211;<\/sup><\/td><td>One 2+ needs two nitrates; bracket the compound ion<\/td><td>Ca(NO<sub>3<\/sub>)<sub>2<\/sub><\/td><\/tr>\n<tr><td><strong>Ammonium sulfate<\/strong><\/td><td>NH<sub>4<\/sub><sup>+<\/sup>, SO<sub>4<\/sub><sup>2-<\/sup><\/td><td>Two 1+ balance one 2-<\/td><td>(NH<sub>4<\/sub>)<sub>2<\/sub>SO<sub>4<\/sub><\/td><\/tr>\n<tr><td><strong>Iron(III) hydroxide<\/strong><\/td><td>Fe<sup>3+<\/sup>, OH<sup>&#8211;<\/sup><\/td><td>One 3+ needs three 1-<\/td><td>Fe(OH)<sub>3<\/sub><\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>A quick check: the total positive charge equals the total negative charge, and the subscripts are the smallest whole numbers that achieve that. The &#8220;swap the charges&#8221; shortcut gives the same answer but simplify afterwards: Mg<sup>2+<\/sup> with O<sup>2-<\/sup> is MgO, not Mg<sub>2<\/sub>O<sub>2<\/sub>.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> The formula of an ionic compound shows the simplest whole-number ratio of ions that gives no overall charge.<\/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: Build Four Formulae<\/h2>\n<p>Drag the correct formula into each blank; the ion charges are given for you.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-468\" class=\"h5p-iframe\" data-content-id=\"468\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Ionic Formulae Drag: Building Formulae from Ion Charges\"><\/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: Which Formulae Are Wrong?<\/h2>\n<p>Click every formula in the list that has been written incorrectly.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-470\" class=\"h5p-iframe\" data-content-id=\"470\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Ionic Formulae Mark the Words: Spot the Formulae That Are Wrong\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Common Exam Mistakes<\/h2>\n<\/div>\n<ul>\n<li>Writing NaCl<sub>2<\/sub> or MgCl. Check that the charges cancel: Na<sup>+<\/sup> needs one Cl<sup>&#8211;<\/sup>, Mg<sup>2+<\/sup> needs two.<\/li>\n<li>Leaving out brackets: CaNO<sub>32<\/sub> instead of Ca(NO<sub>3<\/sub>)<sub>2<\/sub>.<\/li>\n<li>Giving sulfate as SO<sub>4<\/sub><sup>&#8211;<\/sup> or carbonate as CO<sub>3<\/sub><sup>&#8211;<\/sup>. Both carry a 2- charge.<\/li>\n<li>Writing a molecular formula for a giant lattice. NaCl is a ratio of ions, not a molecule of one sodium and one chlorine.<\/li>\n<li>Forgetting the Roman numeral: iron chloride is ambiguous; FeCl<sub>2<\/sub> is iron(II) chloride and FeCl<sub>3<\/sub> is iron(III) chloride.<\/li>\n<\/ul>\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Charges cancel, smallest ratio, brackets round repeated compound ions.<\/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: Read a Formula Backwards<\/h2>\n<p>Work out the charge on the metal ion from the formula you are given.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-471\" class=\"h5p-iframe\" data-content-id=\"471\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Ionic Formulae MCQ: Reading a Formula Backwards\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card orange\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Two More Ions to Know: Zinc and Silver<\/h2>\n<\/div>\n<p>Zinc and silver are transition-block metals, but unlike most of them they form only one ion each, so their charges must be learned.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Ion<\/th><th>Formula<\/th><th>Typical compounds<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Zinc<\/strong><\/td><td>Zn\u00b2\u207a<\/td><td>ZnO, ZnCl\u2082, ZnSO\u2084, Zn(NO\u2083)\u2082<\/td><\/tr>\n<tr><td><strong>Silver<\/strong><\/td><td>Ag\u207a<\/td><td>AgNO\u2083, AgCl, Ag\u2082O, Ag\u2082SO\u2084<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>Balance them exactly as for Group 2 and Group 1 ions: zinc nitrate needs two nitrate ions for one Zn\u00b2\u207a, Zn(NO\u2083)\u2082; silver sulfate needs two Ag\u207a for one SO\u2084\u00b2\u207b, Ag\u2082SO\u2084.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Zn\u00b2\u207a behaves like a Group 2 ion and Ag\u207a like a Group 1 ion when you write formulae.<\/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: Zinc and Silver<\/h2>\n<p>Only one of these four formulae is written correctly.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-518\" class=\"h5p-iframe\" data-content-id=\"518\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Ionic Formulae MCQ: zinc and silver compounds\"><\/iframe><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card purple\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Where This Sits in the OCR Specification<\/h2>\n<\/div>\n<p>OCR 2.1.2(a) asks you to write the formulae of ionic compounds from ionic charges, predicting the charge from the position of the element in the Periodic Table, and to recall the formulae of the nitrate, carbonate, sulfate, hydroxide, ammonium, zinc and silver ions. The ions and the balancing method on this page cover all of it; the same skill is used every time you write an equation in 2.1.2(b).<\/p>\n<\/article>\n\n<section class=\"ols-related-card\">\n        <h2>Related Topics<\/h2>\n        <p>Continue through this section by linking this page to equations, formulae and mole calculation revision.<\/p>\n        <div class=\"ols-related-grid\">\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/equations-and-reaction-types\/\">Equations and Reaction Types<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-2-compounds-formulae-and-equations\/equations-and-reaction-types\/writing-chemical-equations\/\">Writing Chemical Equations<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-3-amount-of-substance\/mole-calculations\/\">Mole Calculations<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-3-amount-of-substance\/empirical-and-molecular-formulae\/\">Empirical and Molecular Formulae<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-3-amount-of-substance\/calculations-with-solutions-and-gases\/\">Calculations with Solutions and Gases<\/a>\n          <a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/ocr-a\/2-1-1-atomic-structure-and-isotopes\/\">Atomic Structure &amp; The Periodic Table<\/a>\n        <\/div>\n      <\/section>\n\n      <section class=\"ols-attribution-card\">\n        <p><strong>Copyright notice:<\/strong> This OLS revision content, including the explanations, layout, diagrams, tables and embedded learning structure, is authored for Online Learning System by Dr. Mohammed Al-Fatah. 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