{"id":10519,"date":"2026-09-26T11:32:42","date_gmt":"2026-09-26T10:32:42","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/thermal-stability-and-flame-colours\/"},"modified":"2026-10-25T12:11:25","modified_gmt":"2026-10-25T12:11:25","slug":"thermal-stability-and-flame-colours","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/thermal-stability-and-flame-colours\/","title":{"rendered":"Thermal Stability and Flame Colours"},"content":{"rendered":"\n<section class=\"ols-revision-page ols-nature-of-covalent-bonding-9ch0-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-orange: #fff7ed;\n      --grey-text: #667085;\n      --body-text: #1f2937;\n      --border: rgba(28, 36, 75, 0.14);\n      --shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      --inner-shadow: 0 10px 26px rgba(28, 36, 75, 0.08);\n      font-family: Poppins, Arial, sans-serif;\n      color: var(--navy);\n      background: #ffffff;\n    }\n\n    .ols-revision-page * { box-sizing: border-box; }\n    .ols-main { min-width: 0; max-width: 970px; }\n    .ols-breadcrumbs { display: flex; flex-wrap: wrap; gap: 8px; margin: 10px 0 22px; font-size: 15px; color: var(--grey-text); }\n    .ols-breadcrumbs a, .ols-breadcrumbs span { color: var(--grey-text); text-decoration: none; font-weight: 600; }\n    .ols-breadcrumbs a:hover { color: var(--blue); text-decoration: underline; text-underline-offset: 3px; }\n    .ols-title-card, .ols-note-card, .ols-h5p-card, .ols-related-card, .ols-faq-card { background: #ffffff; border: 1px solid var(--border); border-radius: 28px; box-shadow: var(--shadow); padding: 34px; margin-bottom: 24px; overflow: hidden; }\n    .ols-title-card { background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%); }\n    .ols-title-card h1 { margin: 0 0 18px; font-size: clamp(36px, 5vw, 58px); line-height: 1.08; font-weight: 800; letter-spacing: -0.04em; color: #111827; }\n    .ols-page-intro { font-size: 19px; line-height: 1.7; font-weight: 300; color: var(--body-text); margin: 0 0 22px; }\n    .ols-badges { display: flex; flex-direction: column; align-items: flex-start; gap: 12px; margin-bottom: 22px; }\n    .ols-badge { display: inline-flex; align-items: center; padding: 9px 14px; border-radius: 999px; background: #ffffff; border: 1px solid var(--border); font-size: 15px; font-weight: 600; color: var(--navy); }\n    .ols-author { display: flex; align-items: center; gap: 20px; padding: 28px; border-radius: 28px; background: linear-gradient(135deg, #ffffff 0%, #f8fbff 100%); border: 1px solid rgba(28,36,75,0.12); box-shadow: 0 18px 45px rgba(28,36,75,0.10); margin-top: 22px; }\n    .ols-author-avatar-img { width: 92px; height: 92px; border-radius: 50%; object-fit: cover; object-position: center; flex-shrink: 0; border: 4px solid #ffffff; box-shadow: 0 14px 32px rgba(28,36,75,0.18), 0 0 0 1px rgba(28,36,75,0.10); transition: transform 0.25s ease, box-shadow 0.25s ease; }\n    .ols-author:hover .ols-author-avatar-img { transform: scale(1.04); box-shadow: 0 20px 42px rgba(28,36,75,0.22), 0 0 0 1px rgba(28,36,75,0.10); }\n    .ols-author-content { min-width: 0; }\n    .ols-author-title { margin: 0 0 4px; font-size: clamp(24px,3vw,34px); line-height: 1.15; font-weight: 700; color: var(--navy); letter-spacing: -0.03em; }\n    .ols-author-description { margin: 0; font-size: 17px; line-height: 1.7; font-weight: 300; color: var(--grey-text); }\n    .ols-linkedin-pill { display: inline-flex; align-items: center; justify-content: center; gap: 10px; margin-top: 16px; padding: 11px 18px; border-radius: 999px; background: linear-gradient(135deg,#0A66C2,#004182); color: #ffffff; text-decoration: none; font-size: 14px; line-height: 1; font-weight: 700; letter-spacing: 0.01em; box-shadow: 0 10px 22px rgba(10,102,194,0.24); position: relative; overflow: hidden; transition: transform 0.22s ease, box-shadow 0.22s ease; }\n    .ols-linkedin-pill::before { content: \"\"; position: absolute; top: 0; left: -120%; width: 100%; height: 100%; background: linear-gradient(120deg, rgba(255,255,255,0) 0%, rgba(255,255,255,0.28) 50%, rgba(255,255,255,0) 100%); transition: left 0.7s ease; }\n    .ols-linkedin-pill:hover { transform: translateY(-3px) scale(1.03); box-shadow: 0 16px 34px rgba(10,102,194,0.34), 0 0 0 6px rgba(10,102,194,0.10); color: #ffffff; }\n    .ols-linkedin-pill:hover::before { left: 120%; }\n    .ols-linkedin-icon { width: 18px; height: 18px; display: block; flex-shrink: 0; }\n\n    .ols-note-card.soft { background: linear-gradient(135deg, #ffffff 0%, var(--soft-red) 100%); }\n    .ols-note-card.purple { background: linear-gradient(135deg, #ffffff 0%, var(--soft-purple) 100%); }\n    .ols-note-card.orange { background: linear-gradient(135deg, #ffffff 0%, var(--soft-orange) 100%); }\n    .ols-note-title { display: flex; align-items: center; gap: 14px; margin-bottom: 20px; }\n    .ols-note-icon { width: 52px; height: 52px; border-radius: 16px; background: var(--navy); color: #ffffff; display: grid; place-items: center; font-size: 24px; font-weight: 800; flex-shrink: 0; }\n    .ols-note-title h2, .ols-h5p-card h2, .ols-related-card h2, .ols-faq-card h2 { margin: 0; font-size: clamp(28px, 3.5vw, 42px); line-height: 1.15; font-weight: 800; color: #111827; letter-spacing: -0.03em; }\n    .ols-h5p-card h2, .ols-related-card h2, .ols-faq-card h2 { margin-bottom: 14px; }\n    .ols-note-card p, .ols-note-card li { font-size: clamp(15px, 1.25vw, 17px); line-height: 1.65; font-weight: 300; color: var(--body-text); }\n    .ols-h5p-card p, .ols-related-card p, .ols-faq-card p { font-size: clamp(15px, 1.3vw, 18px); line-height: 1.65; font-weight: 300; color: var(--body-text); }\n    .ols-note-card strong, .ols-h5p-card strong, .ols-related-card strong, .ols-faq-card strong { font-weight: 700; color: var(--navy); }\n    .ols-note-card ul, .ols-note-card ol { margin: 0; padding-left: 22px; }\n\n    .ols-key-box { margin-top: 20px; background: var(--soft-green); border: 1px solid rgba(63, 143, 70, 0.25); border-radius: 20px; padding: 18px 20px; }\n    .ols-key-box p { margin: 0; font-weight: 400; color: var(--navy); }\n    .ols-definition-box { background: linear-gradient(135deg, #ffffff, var(--soft-purple)); border: 2px dashed rgba(122, 62, 157, 0.35); border-radius: 24px; padding: 22px 24px; margin-top: 22px; }\n    .ols-definition-box p { margin: 0; color: var(--navy); font-weight: 400; }\n\n    .ols-rule-list { display: grid; gap: 14px; margin-top: 18px; }\n    .ols-rule-item { background: #ffffff; border: 1px solid var(--border); border-left: 5px solid var(--blue); border-radius: 18px; padding: 18px; box-shadow: var(--inner-shadow); }\n    .ols-rule-item h3 { margin: 0 0 8px; font-size: 20px; line-height: 1.25; color: var(--navy); }\n    .ols-rule-item p { margin: 0; font-size: 15px; line-height: 1.6; }\n\n    .ols-figure-card { margin: 26px auto 4px; border: 1px solid var(--border); border-radius: 26px; overflow: hidden; background: #ffffff; box-shadow: var(--inner-shadow); max-width: 100%; }\n    .ols-figure-card.medium { max-width: 820px; }\n    .ols-figure-card.compact { max-width: 700px; }\n    .ols-figure-image { width: 100%; min-height: 260px; display: flex; align-items: center; justify-content: center; background: #ffffff; padding: 20px; }\n    .ols-figure-image img { max-width: 100%; height: auto; display: block; }\n    .ols-figure-caption { padding: 18px 24px 22px; background: linear-gradient(135deg, #ffffff, #f8fbff); border-top: 1px solid var(--border); }\n    .ols-figure-caption p { margin: 0; color: #5f6b85; font-size: clamp(15px, 1.3vw, 17px); line-height: 1.6; font-weight: 300; font-style: italic; }\n    .ols-zoom-card, .ols-zoom-card * { box-sizing: border-box; }\n    .ols-zoom-card { display: block !important; margin: 26px auto 34px !important; border: 1px solid rgba(28, 36, 75, 0.14) !important; border-radius: 26px !important; background: #ffffff !important; box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10) !important; overflow: visible !important; position: relative !important; z-index: 1 !important; isolation: isolate !important; }\n    .ols-zoom-card.medium { max-width: 820px; }\n    .ols-zoom-card.compact { max-width: 700px; }\n    .ols-zoom-card.wide { max-width: 940px; }\n    .ols-zoom-card.slim { max-width: 600px; }\n    .ols-zoom-card:hover { z-index: 50 !important; }\n    .ols-zoom-card-image { display: flex !important; align-items: center !important; justify-content: center !important; width: 100% !important; min-height: 240px !important; padding: 20px !important; background: #ffffff !important; overflow: visible !important; border-top-left-radius: 26px !important; border-top-right-radius: 26px !important; position: relative !important; z-index: 2 !important; }\n    .ols-zoom-card img.ols-zoomable-img { display: block !important; max-width: 100% !important; height: auto !important; border-radius: 18px !important; cursor: zoom-in !important; pointer-events: auto !important; user-select: none !important; -webkit-user-drag: none !important; transform: translateZ(0) scale(1) !important; transform-origin: center center !important; transition: transform 0.32s ease, box-shadow 0.32s ease, filter 0.32s ease !important; position: relative !important; z-index: 2 !important; }\n    @media (hover: hover) and (pointer: fine) { .ols-zoom-card img.ols-zoomable-img:hover { transform: translateZ(0) scale(1.35) !important; box-shadow: 0 28px 70px rgba(28, 36, 75, 0.34) !important; filter: saturate(1.02) contrast(1.01) !important; z-index: 100 !important; } }\n    .ols-zoom-card-caption { padding: 18px 22px 20px !important; background: linear-gradient(135deg, #ffffff, #f8fbff) !important; border-bottom-left-radius: 26px !important; border-bottom-right-radius: 26px !important; position: relative !important; z-index: 1 !important; }\n    .ols-zoom-card-caption p { margin: 0 !important; color: #5f6b85 !important; font-size: 15px !important; line-height: 1.65 !important; font-weight: 300 !important; font-style: italic !important; font-family: Poppins, Arial, sans-serif !important; }\n    .ols-image-lightbox { position: fixed; inset: 0; z-index: 999999; display: none; align-items: center; justify-content: center; padding: 34px; background: rgba(10, 15, 35, 0.86); backdrop-filter: blur(8px); -webkit-backdrop-filter: blur(8px); }\n    .ols-image-lightbox.is-open { display: flex; }\n    .ols-image-lightbox-inner { position: relative; width: min(96vw, 1500px); max-height: 92vh; display: flex; align-items: center; justify-content: center; }\n    .ols-image-lightbox-img { display: block; max-width: 100%; max-height: 92vh; height: auto; width: auto; border-radius: 22px; background: #ffffff; box-shadow: 0 32px 90px rgba(0, 0, 0, 0.45); object-fit: contain; }\n    .ols-image-lightbox-close { position: absolute; top: -18px; right: -18px; width: 46px; height: 46px; border: 0; border-radius: 50%; background: #ffffff; color: var(--navy); font-family: Poppins, Arial, sans-serif; font-size: 28px; line-height: 1; font-weight: 700; cursor: pointer; box-shadow: 0 16px 34px rgba(0, 0, 0, 0.28); display: flex; align-items: center; justify-content: center; transition: transform 0.2s ease, background 0.2s ease, color 0.2s ease; }\n    .ols-image-lightbox-close:hover { transform: scale(1.08); background: var(--blue); color: #ffffff; }\n    @media (max-width: 760px) { .ols-zoom-card { border-radius: 22px !important; overflow: hidden !important; } .ols-zoom-card-image { min-height: auto !important; padding: 12px !important; overflow: hidden !important; border-top-left-radius: 22px !important; border-top-right-radius: 22px !important; } .ols-zoom-card img.ols-zoomable-img, .ols-zoom-card img.ols-zoomable-img:hover { transform: none !important; box-shadow: none !important; } .ols-zoom-card-caption { border-bottom-left-radius: 22px !important; border-bottom-right-radius: 22px !important; } .ols-image-lightbox { padding: 16px; } .ols-image-lightbox-inner { width: 100%; max-height: 88vh; } .ols-image-lightbox-img { max-height: 88vh; border-radius: 16px; } .ols-image-lightbox-close { top: 10px; right: 10px; width: 42px; height: 42px; font-size: 26px; } }\n\n\n    .ols-table-wrap { overflow: hidden; border-radius: 22px; border: 1px solid var(--border); background: #ffffff; margin-top: 18px; }\n    .ols-table { width: 100%; border-collapse: collapse; table-layout: fixed; }\n    .ols-table th { background: var(--navy); color: #ffffff; padding: 16px; text-align: left; font-size: clamp(14px, 1.2vw, 17px); font-weight: 600; overflow-wrap: anywhere; }\n    .ols-table td { padding: 16px; border-bottom: 1px solid var(--border); font-size: clamp(14px, 1.15vw, 16px); line-height: 1.45; color: var(--body-text); vertical-align: top; overflow-wrap: anywhere; }\n    .ols-table tr:last-child td { border-bottom: none; }\n\n    .ols-h5p-card { background: linear-gradient(135deg, #ffffff 0%, #f7f0ff 100%); }\n    .ols-h5p-frame { margin-top: 22px; padding: 18px; border-radius: 24px; background: #ffffff; border: 1px solid var(--border); box-shadow: inset 0 0 0 1px rgba(28, 36, 75, 0.03); }\n\n    .ols-faq-list { display: grid; gap: 14px; margin-top: 18px; }\n    .ols-faq-item { background: #ffffff; border: 1px solid var(--border); border-radius: 18px; padding: 18px 20px; box-shadow: var(--inner-shadow); }\n    .ols-faq-item h3 { margin: 0 0 8px; font-size: 20px; line-height: 1.3; color: var(--navy); }\n    .ols-faq-item p { margin: 0; font-size: 16px; line-height: 1.65; color: var(--body-text); }\n\n    .ols-related-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 16px; margin-top: 18px; }\n    .ols-related-item { border: 1px solid var(--border); border-radius: 18px; padding: 18px; background: #ffffff; color: var(--navy); text-decoration: none; font-weight: 600; line-height: 1.5; transition: transform 0.2s ease, box-shadow 0.2s ease; }\n    .ols-related-item:hover { transform: translateY(-2px); box-shadow: 0 10px 22px rgba(28, 36, 75, 0.08); }\n\n    .ols-course-cta-covalent {\n      width: 100%;\n      margin: 30px 0 24px;\n      font-family: Poppins, Arial, sans-serif;\n    }\n    .ols-course-cta-covalent, .ols-course-cta-covalent * { box-sizing: border-box; }\n    .ols-course-cta-card {\n      overflow: hidden;\n      border-radius: 30px;\n      border: 1px solid var(--border);\n      background: radial-gradient(circle at top left, rgba(37, 99, 235, 0.16), transparent 34%), linear-gradient(135deg, #ffffff 0%, #f8fbff 100%);\n      box-shadow: var(--shadow);\n      padding: 30px;\n    }\n    .ols-course-cta-top {\n      display: grid;\n      grid-template-columns: minmax(260px, 0.9fr) minmax(0, 1.1fr);\n      gap: 28px;\n      align-items: center;\n      margin-bottom: 24px;\n    }\n    .ols-course-cta-image-link { display: block; text-decoration: none; border-radius: 24px; }\n    .ols-course-cta-image {\n      width: 100%;\n      border-radius: 24px;\n      overflow: hidden;\n      border: 1px solid var(--border);\n      background: #ffffff;\n      box-shadow: var(--inner-shadow);\n      transition: transform 0.35s ease, box-shadow 0.35s ease;\n    }\n    .ols-course-cta-image img { width: 100%; height: auto; display: block; transition: transform 0.45s ease; }\n    .ols-course-cta-image-link:hover .ols-course-cta-image { transform: translateY(-8px) scale(1.015); box-shadow: 0 26px 60px rgba(28, 36, 75, 0.18), 0 0 0 1px rgba(37, 99, 235, 0.12); }\n    .ols-course-cta-image-link:hover .ols-course-cta-image img { transform: scale(1.03); }\n    .ols-course-cta-header-row { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 14px; margin-bottom: 18px; }\n    .ols-course-cta-kicker { display: inline-flex; align-items: center; padding: 8px 14px; border-radius: 999px; background: #ffffff; border: 1px solid rgba(37, 99, 235, 0.18); color: var(--blue); font-size: 14px; line-height: 1.2; font-weight: 700; box-shadow: var(--inner-shadow); }\n    .ols-course-cta-covalent h2 { margin: 0 0 14px; font-size: clamp(28px, 3.5vw, 42px); line-height: 1.15; font-weight: 800; letter-spacing: -0.03em; color: #111827; }\n    .ols-course-cta-intro { margin: 0 0 24px; color: var(--body-text); font-size: clamp(16px, 1.4vw, 18px); line-height: 1.7; font-weight: 300; }\n    .ols-course-cta-features { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; margin: 0 0 30px; }\n    .ols-course-feature { background: rgba(255, 255, 255, 0.78); border: 1px solid var(--border); border-radius: 18px; padding: 16px 18px; }\n    .ols-course-feature h3 { margin: 0 0 6px; color: var(--navy); font-size: 18px; line-height: 1.3; font-weight: 800; }\n    .ols-course-feature p { margin: 0; color: var(--body-text); font-size: 15px; line-height: 1.6; font-weight: 300; }\n    .ols-course-cta-bottom { display: flex; justify-content: center; padding-top: 22px; border-top: 1px solid var(--border); }\n    .ols-course-button { display: inline-flex; align-items: center; justify-content: center; padding: 15px 28px; border-radius: 999px; background: var(--navy); color: #ffffff; text-decoration: none; font-size: 16px; line-height: 1.2; font-weight: 800; box-shadow: 0 12px 26px rgba(28, 36, 75, 0.18); transition: transform 0.2s ease, background 0.2s ease, box-shadow 0.2s ease; }\n    .ols-course-button:hover { transform: translateY(-2px); background: var(--blue); color: #ffffff; box-shadow: 0 16px 32px rgba(37, 99, 235, 0.24); }\n    .ols-course-button-top { flex-shrink: 0; padding: 12px 22px; font-size: 15px; }\n\n    .ols-attribution-card {\n      background: linear-gradient(135deg, #ffffff, #f8fbff);\n      border: 1px solid rgba(28, 36, 75, 0.14);\n      border-radius: 28px;\n      box-shadow: 0 18px 45px rgba(28, 36, 75, 0.10);\n      padding: 34px;\n      margin-bottom: 24px;\n      overflow: hidden;\n      font-family: Poppins, Arial, sans-serif;\n      box-sizing: border-box;\n    }\n    .ols-attribution-card, .ols-attribution-card * { box-sizing: border-box; }\n    .ols-attribution-card p { margin: 0; font-size: 14px; line-height: 1.65; font-weight: 300; color: #667085; }\n    .ols-attribution-card strong { font-weight: 700; color: #1C244B; }\n\n    @media (max-width: 1050px) {\n      .ols-main { max-width: none; }\n      .ols-related-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }\n      .ols-course-cta-top { grid-template-columns: 1fr; }\n      .ols-course-cta-image-link { max-width: 520px; margin: 0 auto; }\n    }\n\n    @media (max-width: 760px) {\n      .ols-title-card, .ols-note-card, .ols-h5p-card, .ols-related-card, .ols-faq-card, .ols-attribution-card { padding: 24px 18px; border-radius: 22px; }\n      .ols-note-title { align-items: flex-start; }\n      .ols-related-grid, .ols-course-cta-features { grid-template-columns: 1fr; }\n      .ols-figure-card { border-radius: 22px; }\n      .ols-figure-image { min-height: 210px; padding: 14px; }\n      .ols-figure-caption { padding: 16px; }\n      .ols-table-wrap { border: none; 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}\n      .ols-course-cta-card { padding: 20px; border-radius: 24px; }\n      .ols-course-cta-header-row { align-items: stretch; }\n      .ols-course-button-top, .ols-course-button { width: 100%; }\n    }\n  \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\n    \/* inline checks (H5P re-flow, Sep 2026) *\/\n    .ols-h5p-card.ols-h5p-inline { padding: 26px 28px; border-left: 6px solid #7c3aed; }\n    .ols-h5p-card.ols-h5p-inline h2 { font-size: clamp(20px, 2.2vw, 27px); letter-spacing: -0.02em; }\n    .ols-h5p-card.ols-h5p-inline > p { margin: 8px 0 0; }\n    .ols-h5p-card.ols-h5p-inline .ols-h5p-frame { margin-top: 16px; padding: 14px; border-radius: 20px; }\n    .ols-h5p-kicker { display: inline-block; margin-bottom: 10px; padding: 5px 12px; border-radius: 999px; background: #ede9fe; color: #5b21b6; font-size: 12px; font-weight: 700; letter-spacing: 0.06em; text-transform: uppercase; }\n    .ols-h5p-card.ols-h5p-recap { border-left-color: #c9973a; background: linear-gradient(135deg, #ffffff 0%, #fff8e8 100%); }\n    .ols-h5p-recap .ols-h5p-kicker { background: #fdf0d2; color: #8a5a00; }\n    @media (max-width: 760px) { .ols-h5p-card.ols-h5p-inline { padding: 20px 16px; } }\n<\/style>\n\n  <aside class=\"ols-sidebar\">\n  <div class=\"ols-sidebar-header\">\n    <h3>Revision Notes<\/h3>\n    <p>A Level Chemistry<\/p>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Topic 4 Inorganic Chemistry and The Periodic Table<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/\">Topic 4 Overview<\/a>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/\">Groups 1 and 2<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/trends-down-groups-1-and-2\/\">Trends Down Groups 1 and 2<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/reactions-of-the-group-1-and-2-elements\/\">Reactions of the Group 1 and 2 Elements<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/oxides-hydroxides-and-carbonates\/\">Oxides, Hydroxides and Carbonates<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/solubility-trends-and-the-sulfate-test\/\">Solubility Trends and the Sulfate Test<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/thermal-stability-and-flame-colours\/\">Thermal Stability and Flame Colours<\/a>\n          <\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/group-7-halogens\/\">Group 7 Halogens<\/a>\n        <ul class=\"ols-subtopic-list\">\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/group-7-halogens\/trends-in-the-halogens\/\">Trends in the Halogens<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/group-7-halogens\/halogens-as-oxidising-agents\/\">Halogens as Oxidising Agents<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/group-7-halogens\/disproportionation-reactions-of-chlorine\/\">Disproportionation Reactions of Chlorine<\/a>\n          <\/li>\n          <li>\n            <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/group-7-halogens\/halide-ions-reducing-agents-and-tests\/\">Halide Ions: Reducing Agents and Tests<\/a>\n          <\/li>\n        <\/ul>\n      <\/li>\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/inorganic-analysis\/\">Inorganic Analysis: Tests for Ions<\/a>\n      <\/li>\n    <\/ul>\n  <\/div>\n\n  <div class=\"ols-topic-group\">\n    <h4>Next Topics<\/h4>\n\n    <ul class=\"ols-topic-list\">\n      <li>\n        <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/\">Topic 5 Formulae, Equations &amp; Amounts<\/a>\n      <\/li>\n      <li>\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      <\/li>\n      <li>\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>\n      <\/li>\n    <\/ul>\n  <\/div>\n<\/aside>\n\n<script>\r\n(function() {\r\n  function normalisePath(path) {\r\n    return String(path || '')\r\n      .split('?')[0]\r\n      .split('#')[0]\r\n      .replace(\/\\\/+$\/, '')\r\n      .toLowerCase();\r\n  }\r\n\r\n  function highlightActive() {\r\n    var sidebar = document.querySelector('.ols-sidebar');\r\n    if (!sidebar) return false;\r\n\r\n    var currentPath = normalisePath(window.location.pathname);\r\n    var links = sidebar.querySelectorAll('a[href]');\r\n    var matched = null;\r\n    var matchedLength = 0;\r\n\r\n    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      a.removeAttribute('data-ols-disabled-parent');\r\n    });\r\n\r\n    links.forEach(function(a) {\r\n      try {\r\n        var href = a.getAttribute('href');\r\n        if (!href || href === '#' || href.charAt(0) === '#') return;\r\n        var linkPath = normalisePath(new URL(href, window.location.origin).pathname);\r\n        if (!linkPath) return;\r\n        if (currentPath === linkPath || currentPath.indexOf(linkPath + '\/') === 0) {\r\n          if (linkPath.length > matchedLength) {\r\n            matched = a;\r\n            matchedLength = linkPath.length;\r\n          }\r\n        }\r\n      } catch(e) {}\r\n    });\r\n\r\n    if (matched) {\r\n      var matchedLi = matched.closest('li');\r\n      var parentSub = matched.closest('.ols-subtopic-list');\r\n\r\n      if (parentSub) {\r\n        if (matchedLi) {\r\n          matchedLi.classList.add('active');\r\n          matched.setAttribute('aria-current', 'page');\r\n        }\r\n        var parentLi = parentSub.closest('li');\r\n        if (parentLi) {\r\n          parentLi.classList.add('parent-active', 'active-main');\r\n          var parentLink = parentLi.querySelector(':scope > a');\r\n          if (parentLink) {\r\n            parentLink.setAttribute('aria-current', 'true');\r\n            parentLink.setAttribute('tabindex', '-1');\r\n            parentLink.setAttribute('data-ols-disabled-parent', '1');\r\n          }\r\n        }\r\n      } else {\r\n        if (matchedLi) {\r\n          matchedLi.classList.add('parent-active', 'active-main');\r\n          matched.setAttribute('aria-current', 'page');\r\n          matched.setAttribute('tabindex', '-1');\r\n          matched.setAttribute('data-ols-disabled-parent', '1');\r\n        }\r\n      }\r\n    }\r\n\r\n    return true;\r\n  }\r\n\r\n  if (!highlightActive()) {\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-4-inorganic-chemistry-and-the-periodic-table\/\">Topic 4 Inorganic Chemistry and The Periodic Table<\/a> \/\n<a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/\">Groups 1 and 2<\/a> \/\n<span>Thermal Stability and Flame Colours<\/span>\n<\/nav>\n\n      <header class=\"ols-title-card\">\n        <h1>Thermal Stability and Flame Colours<\/h1>\n        <p class=\"ols-page-intro\">A concise revision guide to the thermal decomposition of the Group 1 and 2 nitrates and carbonates, the trend in stability explained by cation size, charge and polarisation, how to show the patterns experimentally, and the flame colours and their cause.<\/p>\n\n        <div class=\"ols-badges\">\n<div class=\"ols-badge\">Paper 1 and 2<\/div>\n<div class=\"ols-badge\">Topic 4A: Group 2<\/div>\n<div class=\"ols-badge\">9CH0\/01<\/div>\n<\/div>\n      <\/header>\n<!-- 3D card: group2-thermal-stability (26 Sep 2026) -->\n<!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. 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span{display:block;font-size:11.5px;color:#7d8399;font-weight:400;margin-bottom:3px;}\r\n.ols-g2c-001 .g2c-fact strong{display:block;font-size:15px;font-weight:600;color:#1C244B;}\r\n.ols-g2c-001 .g2c-key{margin-top:16px;display:flex;gap:20px;flex-wrap:wrap;font-size:12.5px;font-weight:400;color:#5a6180;}\r\n.ols-g2c-001 .g2c-key i{display:inline-block;width:13px;height:13px;border-radius:3px;margin-right:7px;vertical-align:-2px;border:1px solid rgba(28,36,75,0.18);}\r\n@media (max-width:760px){\r\n  .ols-g2c-001{padding:26px;border-radius:22px;}\r\n  .ols-g2c-001 h2.g2c-title{font-size:20.5px;}\r\n  .ols-g2c-001 p.g2c-sub{font-size:13.5px;}\r\n  .ols-g2c-001 .g2c-stage{height:440px;}\r\n  .ols-g2c-001 .g2c-rowlab{min-width:100%;}\r\n  .ols-g2c-001 .g2c-seg button{padding:9px 12px;font-size:13px;}\r\n  .ols-g2c-001 .g2c-lab{font-size:10px;padding:4px 7px;}\r\n  .ols-g2c-001 .g2c-lab.l-eq{font-size:10.5px;}\r\n  .ols-g2c-001 .g2c-caption{font-size:10.5px;padding:5px 9px;max-width:100%;right:14px;}\r\n  .ols-g2c-001 .g2c-badge{font-size:10.5px;padding:4px 9px;}\r\n  .ols-g2c-001 .g2c-badge.b-eq{font-size:11px;}\r\n  .ols-g2c-001 .g2c-badges{max-width:80%;}\r\n  .ols-g2c-001 .g2c-info{padding:18px;}\r\n}\r\n@media (max-width:480px){ .ols-g2c-001 .g2c-hint{display:none;} }\r\n@media (prefers-reduced-motion:reduce){ .ols-g2c-001 .g2c-seg button,.ols-g2c-001 .g2c-pill{transition:none;} }\r\n.ols-cc-g2c-001{font-family:'Poppins',system-ui,-apple-system,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;margin:10px auto 0;text-align:center;font-size:11px;font-style:italic;color:#aab0c0;}\r\n.ols-cc-g2c-001 a{color:#aab0c0;text-decoration:none;}\r\n.ols-cc-g2c-001 a:hover{text-decoration:underline;}\r\n<\/style>\r\n<div class=\"g2c-head\">\r\n  <h2 class=\"g2c-title\">Polarisation and the Thermal Stability of Group 2 Carbonates<\/h2>\r\n  <p class=\"g2c-sub\">Small, highly charged cations distort the carbonate ion more, so it breaks up at a lower temperature. Down Group 2 the carbonates and nitrates get more stable.<\/p>\r\n<\/div>\r\n<div class=\"g2c-stage\" id=\"g2cStage\">\r\n  <canvas class=\"g2c-canvas\" id=\"g2cCanvas\"><\/canvas>\r\n  <div class=\"g2c-overlay\" id=\"g2cOverlay\"><\/div>\r\n  <div class=\"g2c-caption\" id=\"g2cCaption\"><\/div>\r\n  <div class=\"g2c-hint\" id=\"g2cHint\">Drag to rotate<\/div>\r\n  <div class=\"g2c-badges\" id=\"g2cBadges\"><\/div>\r\n<\/div>\r\n<div class=\"g2c-controls\">\r\n  <div class=\"g2c-row\">\r\n    <span class=\"g2c-rowlab\">Step<\/span>\r\n    <div class=\"g2c-seg\" role=\"group\" aria-label=\"Step\">\r\n      <button type=\"button\" data-step=\"1\" aria-pressed=\"true\"><span class=\"g2c-n\">1<\/span>The cations<\/button>\r\n      <button type=\"button\" data-step=\"2\" aria-pressed=\"false\"><span class=\"g2c-n\">2<\/span>Polarising the anion<\/button>\r\n      <button type=\"button\" data-step=\"3\" aria-pressed=\"false\"><span class=\"g2c-n\">3<\/span>Mg\u00b2\u207a against Ba\u00b2\u207a<\/button>\r\n      <button type=\"button\" data-step=\"4\" aria-pressed=\"false\"><span class=\"g2c-n\">4<\/span>Decomposition<\/button>\r\n      <button type=\"button\" data-step=\"5\" aria-pressed=\"false\"><span class=\"g2c-n\">5<\/span>Nitrates<\/button>\r\n    <\/div>\r\n  <\/div>\r\n  <div class=\"g2c-row\">\r\n    <span class=\"g2c-rowlab\">View<\/span>\r\n    <button type=\"button\" class=\"g2c-pill\" id=\"g2cResetV\">Reset view<\/button>\r\n  <\/div>\r\n<\/div>\r\n<div class=\"g2c-info\">\r\n  <h3 id=\"g2cInfoTitle\"><\/h3>\r\n  <p id=\"g2cInfoText\"><\/p>\r\n  <div class=\"g2c-facts\" id=\"g2cFacts\"><\/div>\r\n  <div class=\"g2c-key\">\r\n    <span><i style=\"background:#38968a\"><\/i>Group 2 cation, M\u00b2\u207a<\/span>\r\n    <span><i style=\"background:#464a56\"><\/i>C<\/span>\r\n    <span><i style=\"background:#d63a34\"><\/i>O<\/span>\r\n    <span><i style=\"background:#3462d2\"><\/i>N<\/span>\r\n    <span><i style=\"background:#9ab8ee\"><\/i>electron density<\/span>\r\n    <span><i style=\"background:#96501c\"><\/i>NO\u2082, brown gas<\/span>\r\n  <\/div>\r\n<\/div>\r\n<\/section>\r\n<p class=\"ols-cc-g2c-001\">&copy; Dr. Mohammed Al-Fatah &#8211; <a href=\"https:\/\/www.onlinelearningsystem.net\" target=\"_blank\" rel=\"noopener\">onlinelearningsystem.net<\/a><\/p>\r\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/JS\/group2-thermal-stability.js?v=20261025p\"><\/script>\n\n\n      <article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">1<\/div>\n<h2>Thermal Decomposition of the Carbonates<\/h2>\n<\/div>\n<p>On strong heating a metal carbonate breaks down to the metal oxide and carbon dioxide. The <strong>Group 2 carbonates all decompose<\/strong> in a Bunsen flame, and the temperature needed rises down the group.<\/p>\n<div class=\"ols-table-wrap\"><table class=\"ols-table\"><thead><tr><th>Carbonate<\/th><th>Decomposes at about<\/th><\/tr><\/thead><tbody><tr><td><strong>Magnesium carbonate<\/strong><\/td><td>350 \u00b0C<\/td><\/tr><tr><td><strong>Calcium carbonate<\/strong><\/td><td>840 \u00b0C<\/td><\/tr><tr><td><strong>Strontium carbonate<\/strong><\/td><td>1100 \u00b0C<\/td><\/tr><tr><td><strong>Barium carbonate<\/strong><\/td><td>1300 \u00b0C<\/td><\/tr><\/tbody><\/table><\/div>\n<p>MgCO\u2083 \u2192 MgO + CO\u2082 &nbsp;&nbsp; CaCO\u2083 \u2192 CaO + CO\u2082<\/p>\n<p>The <strong>Group 1 carbonates are more stable<\/strong>. Sodium and potassium carbonate do not decompose at Bunsen temperatures at all; only lithium carbonate, whose ion is the smallest, breaks down: Li\u2082CO\u2083 \u2192 Li\u2082O + CO\u2082.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Key idea:<\/strong> Thermal stability increases down each group, and Group 1 carbonates are more stable than the Group 2 carbonates beside them.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">2<\/div>\n<h2>Thermal Decomposition of the Nitrates<\/h2>\n<\/div>\n<p>The nitrates show the same pattern, but the products differ between the groups. Most <strong>Group 1 nitrates<\/strong> decompose only to the nitrite and oxygen:<\/p>\n<p>2NaNO\u2083 \u2192 2NaNO\u2082 + O\u2082 &nbsp;&nbsp; 2KNO\u2083 \u2192 2KNO\u2082 + O\u2082<\/p>\n<p>The <strong>Group 2 nitrates<\/strong>, and again lithium nitrate, decompose further to the oxide, nitrogen dioxide and oxygen. The brown fumes of nitrogen dioxide are the sign of this reaction:<\/p>\n<p>2Mg(NO\u2083)\u2082 \u2192 2MgO + 4NO\u2082 + O\u2082 &nbsp;&nbsp; 4LiNO\u2083 \u2192 2Li\u2082O + 4NO\u2082 + O\u2082<\/p>\n<p>The temperature needed rises down Group 2, as with the carbonates.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Exam focus:<\/strong> Learn both nitrate equations. A Group 2 nitrate gives three products; a Group 1 nitrate (other than lithium) gives two.<\/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\/09\/t8x-nitrateheat.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\/t8x-nitrateheat.jpg\" alt=\"Two-lane poster comparing Group 1 nitrates giving nitrite and oxygen with Group 2 nitrates giving oxide, NO\u2082 and oxygen.\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Most Group 1 nitrates lose only oxygen to form the nitrite, but Group 2 nitrates and lithium nitrate break down further to the oxide, brown nitrogen dioxide and oxygen.<\/p><\/div>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Check: Decomposition Products<\/h2>\n<p>Write the decomposition equation and name the gases for carbonates and nitrates not shown above.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-875\" class=\"h5p-iframe\" data-content-id=\"875\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Redox and Groups Fill In: Decomposition Products\"><\/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>Why the Trend Exists: Polarisation<\/h2>\n<\/div>\n<p>The carbonate and nitrate ions are large anions with electron density spread over several oxygen atoms.<\/p>\n<p>A small, highly charged cation has a high <strong>charge density<\/strong> and pulls that electron cloud towards itself, <strong>polarising<\/strong> the anion.<\/p>\n<p>The distortion weakens the C\u2013O or N\u2013O bonds, so less energy is needed to break the ion apart, and the compound decomposes at a lower temperature.<\/p>\n<p>Down each group the cation gets larger, its charge density falls, it polarises the anion less, and the compound is <strong>more stable<\/strong>.<\/p>\n<p>Across from Group 1 to Group 2 the charge doubles, so a 2+ ion polarises far more than a 1+ ion of similar size. This is why Group 2 carbonates and nitrates are the less stable set.<\/p>\n\n\n<div class=\"ols-key-box\">\n<p><strong>Exam sentence:<\/strong> Magnesium carbonate decomposes at a lower temperature than barium carbonate because the Mg\u00b2\u207a ion is smaller, so it has a higher charge density and polarises the carbonate ion more, weakening the C\u2013O bonds.<\/p>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Check: Explaining Stability<\/h2>\n<p>Choose the correct polarisation argument and rank compounds by stability using ionic radius and charge.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"876\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">4<\/div>\n<h2>Showing the Trend Experimentally<\/h2>\n<\/div>\n<p>To compare the thermal stability of carbonates, heat the same amount in moles of each carbonate with the same Bunsen flame and pass the gas through limewater.<\/p><p>The <strong>time taken for the limewater to turn cloudy<\/strong> is a measure of how easily the carbonate decomposes: the longer the time, the more stable the carbonate.<\/p><p>For the nitrates, time how long the brown fumes take to appear, or test for oxygen with a glowing splint.<\/p>\n<p>The comparison is only fair if the amount of solid, the flame and the apparatus are the same each time, and the test is repeated to check the ranking.<\/p>\n<div class=\"ols-key-box\">\n<p><strong>Technique point:<\/strong> Use the same number of moles, not the same mass, because the compounds have different molar masses and the amount of gas that can form depends on the moles of anion.<\/p>\n<\/div>\n<\/article>\n<article class=\"ols-note-card soft\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">5<\/div>\n<h2>Flame Colours<\/h2>\n<\/div>\n<p>Compounds of the s-block metals give <strong>characteristic colours<\/strong> in a Bunsen flame. A nichrome wire is cleaned in concentrated hydrochloric acid, dipped in the solid or solution, and held in a hot blue flame.<\/p>\n<div class=\"ols-table-wrap\">\n<table class=\"ols-table\">\n<thead>\n<tr><th>Metal<\/th><th>Flame colour<\/th><th>Metal<\/th><th>Flame colour<\/th><\/tr>\n<\/thead>\n<tbody>\n<tr><td><strong>Lithium<\/strong><\/td><td>red<\/td><td>Magnesium<\/td><td>no colour (burns with a bright white light)<\/td><\/tr>\n<tr><td><strong>Sodium<\/strong><\/td><td>yellow<\/td><td>Calcium<\/td><td>brick red<\/td><\/tr>\n<tr><td><strong>Potassium<\/strong><\/td><td>lilac<\/td><td>Strontium<\/td><td>red<\/td><\/tr>\n<tr><td><strong>Rubidium<\/strong><\/td><td>red<\/td><td>Barium<\/td><td>apple green<\/td><\/tr>\n<tr><td><strong>Caesium<\/strong><\/td><td>blue<\/td><td><\/td><td><\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The colour comes from <strong>electron transitions<\/strong>. The heat of the flame promotes electrons in the metal ions to higher energy levels. When they fall back to lower levels they release the energy difference as light.<\/p>\n<p>The energy gaps are fixed for each element and correspond to particular frequencies in the visible region, so each element gives its own colour.<\/p>\n<p>Magnesium ions have no transition in the visible region, so magnesium compounds give no flame colour.<\/p>\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\/redox-groups-flame-colours.png\" 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\/redox-groups-flame-colours.png\" alt=\"Flame colours of Group 1 and 2 ions and the electron transitions that cause them\">\n<\/a>\n<\/div>\n<div class=\"ols-zoom-card-caption\"><p>Each flame colour is a fingerprint of the energy gaps in that element: the electron is promoted by the heat and emits light of a fixed frequency as it falls back.<\/p><\/div>\n<\/div>\n<div class=\"ols-key-box\">\n<p><strong>Exam wording:<\/strong> &#8220;Electrons are excited to higher energy levels by the heat; as they fall back to lower levels they emit light of a specific frequency, which corresponds to a colour in the visible region.&#8221;<\/p>\n<\/div>\n<\/article>\n<section class=\"ols-h5p-card ols-h5p-inline\">\n<span class=\"ols-h5p-kicker\">Check your understanding<\/span>\n<h2>Check: Flame Colours and Their Cause<\/h2>\n<p>Identify metals from flame colours and choose the correct explanation of why the light is emitted.<\/p>\n<div class=\"ols-h5p-frame\"><div class=\"h5p-content\" data-content-id=\"877\"><\/div><\/div>\n<\/section>\n<article class=\"ols-note-card\">\n<div class=\"ols-note-title\">\n<div class=\"ols-note-icon\">6<\/div>\n<h2>Common Exam Points<\/h2>\n<\/div>\n<h3>Explain why the thermal stability of carbonates increases down Group 2<\/h3><p>The cation gets larger, its charge density falls, it polarises the carbonate ion less, so the C\u2013O bonds are less weakened and more energy is needed to break them.<\/p>\n<h3>Write the equation for the decomposition of a Group 2 nitrate<\/h3><p>2M(NO\u2083)\u2082 \u2192 2MO + 4NO\u2082 + O\u2082.<\/p>\n<h3>Explain the origin of a flame colour<\/h3><p>Electrons promoted by heat fall back to lower energy levels and emit light of a frequency fixed by the energy gap.<\/p>\n<h3>Do not say<\/h3><p>&#8220;Barium carbonate has stronger ionic bonds so it is more stable&#8221;; &#8220;sodium nitrate gives brown fumes&#8221;; &#8220;the flame colour comes from the anion&#8221;.<\/p>\n<\/article>\n<section class=\"ols-faq-card\">\n<h2>FAQs<\/h2>\n<p>Use these quick answers to check thermal stability and flame colours.<\/p>\n\n<div class=\"ols-faq-list\">\n<div class=\"ols-faq-item\">\n<h3>Why does thermal stability increase down the group?<\/h3>\n<p>The cation gets larger, so its charge density falls and it polarises the carbonate or nitrate ion less, leaving the C\u2013O or N\u2013O bonds stronger.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why are Group 1 carbonates more stable than Group 2 carbonates?<\/h3>\n<p>A 1+ ion has a lower charge density than a 2+ ion of similar size, so it polarises the anion less.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>What are the products when a Group 2 nitrate decomposes?<\/h3>\n<p>The metal oxide, nitrogen dioxide (brown gas) and oxygen: 2M(NO\u2083)\u2082 \u2192 2MO + 4NO\u2082 + O\u2082.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>How is a flame colour produced?<\/h3>\n<p>Heat promotes electrons to higher energy levels; as they fall back they emit light of a fixed frequency, which is a colour in the visible region.<\/p>\n<\/div>\n\n<div class=\"ols-faq-item\">\n<h3>Why does magnesium give no flame colour?<\/h3>\n<p>The energy gaps in magnesium ions do not correspond to visible light, so no colour is seen, although burning magnesium gives a bright white light.<\/p>\n<\/div>\n<\/div>\n<\/section>\n\n      <!-- author card (moved to the end, 10 Oct 2026) -->\n      <div class=\"ols-author\">\n\n    <img decoding=\"async\"\n      class=\"ols-author-avatar-img\"\n      src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Author-Profile.jpeg\"\n      alt=\"Dr. Mohammed Al-Fatah\"\n    >\n\n    <div class=\"ols-author-content\">\n\n      <h2 class=\"ols-author-title\">\n        Written by:<br><span>Dr. Mohammed Al-Fatah<\/span>\n      <\/h2>\n\n      <p class=\"ols-author-description\">\n        Chemistry specialist revision notes for A Level Chemistry.\n      <\/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\n    <\/div>\n\n  <\/div>\n\n<section class=\"ols-related-card\">\n<h2>Related Topic 4 Groups 1 and 2 Pages<\/h2>\n<p>Use these pages to connect the ideas across Topic 4 Groups 1 and 2 and the rest of the course.<\/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-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/trends-down-groups-1-and-2\/\">Trends Down Groups 1 and 2<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/reactions-of-the-group-1-and-2-elements\/\">Reactions of the Group 1 and 2 Elements<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/oxides-hydroxides-and-carbonates\/\">Oxides, Hydroxides and Carbonates<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/solubility-trends-and-the-sulfate-test\/\">Solubility Trends and the Sulfate Test<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/groups-1-and-2\/\">Groups 1 and 2 Overview<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-4-inorganic-chemistry-and-the-periodic-table\/inorganic-analysis\/\">Inorganic Analysis: Tests for Ions<\/a>\n<a class=\"ols-related-item\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/revision-notes\/a-level-chemistry\/edexcel\/topic-5-formulae-equations-and-amounts-of-substance\/calculations-with-solutions-and-gases\/titration-calculations\/\">Titration Calculations<\/a>\n<\/div>\n<\/section>\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. 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