Periodic table | Definition, Elements, Groups, Charges, Trends, & Facts

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top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/periodic-table">Introduction & Top Questions</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref80826"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/periodic-table#ref80826">History of the periodic law</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref80827"><a class="w-100 link-gray-900" href="/science/periodic-table#ref80827">Classification of the elements</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref80828"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table">The first periodic table</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref80829"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80829">Other versions of the periodic table</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref80830"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80830">Predictive value of the periodic law</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref80831"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80831">Discovery of new elements</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref80832"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80832">Significance of atomic numbers</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref80833"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80833">Elucidation of the periodic law</a></li></ul></li></ul></div></li><li data-target="#ref80834"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table">The periodic table</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref80835"><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table#ref80835">Periods</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref80836"><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table#ref80836">Groups</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref80837"><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table#ref80837">Classification of elements into groups</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref80838"><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table#ref80838">Periodic trends in properties</a></li></ul></li></ul></div></li><li data-target="#ref80839"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/periodic-table/The-basis-of-the-periodic-system">The basis of the periodic system</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref80840"><a class="w-100 link-gray-900" href="/science/periodic-table/The-basis-of-the-periodic-system#ref80840">Electronic structure</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref80841"><a class="w-100 link-gray-900" href="/science/periodic-table/Periodicity-of-properties-of-the-elements">Periodicity of properties of the elements</a></li></ul></div></li><li data-target="#ref80842"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/periodic-table/Periodicity-of-properties-of-the-elements#ref80842">Other chemical and physical classifications</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/periodic-table/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/periodic-table">Quick Facts & Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" href="https://www.britannica.com/science/periodic-table/images-videos">Images, Videos & Interactives</a> <div class="slider js-slider position-relative d-inline-flex align-items-center mw-100 "> <div class="slider-container js-slider-container overflow-hidden d-flex overflow-hidden text-nowrap ml-15"> <a href="https://cdn.britannica.com/13/150513-050-4C886073/version-periodic-table-elements-information-one-element.jpg" data-href="/media/1/451929/158579" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/13/150513-049-4C886073/version-periodic-table-elements-information-one-element.jpg" 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Let us know if you have suggestions to improve this article (requires login). </div> <div class="type-menu"> <label for="feedback-type" class="label mb-10">Feedback Type</label> <select id="feedback-type" class="form-select mb-30" name="feedbackTypeId" required> <option value="" selected="selected">Select a type (Required)</option> <option value="1">Factual Correction</option> <option value="2">Spelling/Grammar Correction</option> <option value="3">Link Correction</option> <option value="4">Additional Information</option> <option value="5">Other</option> </select> </div> <label for="feedback" class="label mb-10">Your Feedback</label> <textarea id="feedback" class="form-control mb-30" name="feedback" maxlength="3000" rows="7" required></textarea> <button class="btn btn-blue" type="submit">Submit Feedback</button> </form> <div class="success-messaging d-none mt-30"> <div class="title">Thank you for your feedback</div> <p>Our editors will review what you’ve submitted and determine whether to revise the article.</p> </div> </div> </div> <div class="md-websites-modal size-lg d-none"> <div class="md-modal-body"> <div class="h2 font-serif pb-15 border-bottom font-weight-bold"> External Websites </div> <div class="pb-20"> <ul class="list-unstyled mt-20 lh-lg"> <li><a class="external" href="https://core.ac.uk/download/pdf/295731938.pdf" target="_blank" rel="noopener ">CORE - Causal Explanation and the Periodic Table</a></li> <li><a class="external" href="https://uen.pressbooks.pub/introductorychemistry/chapter/the-periodic-table-2/" target="_blank" rel="noopener ">UEN Digital Press with Pressbooks - Introductory Chemistry - The Periodic Table</a></li> <li><a class="external" href="https://www.jetir.org/papers/JETIRFH06105.pdf" target="_blank" rel="noopener ">Journal of Emerging Technologies and Innovative Research - A Review Paper on Periodic Table</a></li> <li><a class="external" href="https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introductory_Chemistry_(CK-12)/06%3A_The_Periodic_Table" target="_blank" rel="noopener ">Chemistry LibreTexts - The Periodic Table</a></li> <li><a class="external" href="https://origins.osu.edu/milestones/mendeleev-periodic-table-UN-chemistry-radioactivity-noble-gases" target="_blank" rel="noopener ">Ohio State University - Origins - Mendeleev's Periodic Table</a></li> <li><a class="external" href="https://pubchem.ncbi.nlm.nih.gov/periodic-table/" target="_blank" rel="noopener ">National Center for Biotechnology Information - PubChem - Periodic Table of Elements</a></li> <li><a class="external" href="https://www.neok12.com/Periodic-Table.htm" target="_blank" rel="noopener nofollow">NeoK12 - Educational Videos and Games for School Kids - Periodic Table</a></li> <li><a class="external" href="https://www.livescience.com/25300-periodic-table.html" target="_blank" rel="noopener ">LiveScience - Periodic Table of the Elements</a></li> <li><a class="external" href="https://www.khanacademy.org/science/chemistry/periodic-table/copy-of-periodic-table-of-elements/a/the-periodic-table-electron-shells-and-orbitals-article" target="_blank" rel="noopener ">Khan Academy - The periodic table, electron shells, and orbitals</a></li> <li><a class="external" href="https://people.wou.edu/~courtna/ch412/perhist.htm" target="_blank" rel="noopener nofollow">Western Oregon University - A brief history of the development of Periodic Table</a></li> <li><a class="external" href="https://www.rsc.org/periodic-table" target="_blank" rel="noopener ">Royal Society of Chemistry - Patterns in the Periodic Table</a></li> </ul> </div> <div class="md-websites-ebk-title">Britannica Websites</div> <div class="md-websites-ebk-subtitle">Articles from Britannica Encyclopedias for elementary and high school students.</div> <ul class="list-unstyled bps-topic-web-sites lh-lg"> <li><a class="external" href="https://kids.britannica.com/kids/article/periodic-table/600334" target="_blank" rel="noopener">periodic table - Children's Encyclopedia (Ages 8-11)</a></li> <li><a class="external" href="https://kids.britannica.com/students/article/periodic-table/276364" target="_blank" rel="noopener">periodic table - Student Encyclopedia (Ages 11 and up)</a></li> </ul> </div> </div> </div> </div> <div class="toc-header-marker"></div> <button class="ai-ask-button btn border-2 js-header-ai-ask-button d-none btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10"> Ask the Chatbot a Question </button> <div class="caption alternate-titles">Also known as: periodic table of the elements</div> <div class="md-byline module-spacing "> <div class="font-serif font-12"> <span class="written-by text-gray-700"> Written by </span> <div class="editor-popover popover p-0"> <a class="d-block p-20 gtm-byline font-12 byline-contributor" href="/contributor/Linus-C-Pauling/2265" > <div class="editor-title font-16 font-weight-bold">Linus C. Pauling</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Research Professor, Linus Pauling Institute of Science and Medicine, Palo Alto, California, 1973–94. Professor of Chemistry, Stanford University, California, 1969–74. Nobel Prize for Chemistry, 1954; Nobel...</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Linus C. Pauling</span>, <div class="editor-popover popover p-0"> <a class="d-block p-20 gtm-byline font-12 byline-contributor" href="/contributor/JJ-Lagowski/1666" > <div class="editor-title font-16 font-weight-bold">J.J. Lagowski</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Professor of Chemistry, University of Texas at Austin. Author of <i>The Chemical Bond.</i></div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> J.J. Lagowski</span><span class="text-gray-700 mx-5">•</span><a class="see-all border-gray-700 gtm-byline" rel="nofollow" href="https://www.britannica.com/science/periodic-table/additional-info#contributors">All</a> </div> <div class="font-serif font-12 text-gray-700"> <span class="qa-fact-checked-by">Fact-checked by</span> <div class="editor-popover popover p-0"> <a class="d-block p-20 font-12" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <span class="text-gray-700"> Last Updated: <time datetime="2024-11-10T00:00:00CST" >Nov 10, 2024</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/science/periodic-table/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </button> </div> <div class="feature-block breakout"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="158579" data-asm-type="interactive"><div class="md-assembly-wrapper card-media " data-type="interactive"><div style="width:100%; aspect-ratio: 2000 / 1500"><iframe width="100%" height="100%" src="https://cdn.britannica.com/13/150513-101-275ABE9E/default.html" scrolling="no" style="border:none"></iframe></div></div></figure></div></div><div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>In full: </dt> <dd>periodic table of the elements</dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Key People: </dt> <dd><a href="/biography/Dmitri-Mendeleev" topicid="374765">Dmitri Mendeleev</a></dd> <dd><a href="/biography/Lothar-Meyer" topicid="379472">Lothar Meyer</a></dd> <dd><a href="/biography/Paul-Emile-Lecoq-de-Boisbaudran" topicid="334399">Paul-Émile Lecoq de Boisbaudran</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/science/chemical-element" topicid="108636">chemical element</a></dd> <dd><a href="/science/atom" topicid="41549">atom</a></dd> <dd><a href="/science/group-periodic-table" topicid="247062">group</a></dd> <dd><a href="/science/periodic-law" topicid="451901">periodic law</a></dd> <dd><a href="/science/period-chemistry" topicid="451862">period</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>On the Web: </dt> <dd><a href="https://core.ac.uk/download/pdf/295731938.pdf" target="_blank">CORE - Causal Explanation and the Periodic Table</a> (Oct. 28, 2024)</dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/periodic-table"> See all related content </a> </div> </div> </div> </div><script type="application/ld+json"> { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type" : "Question", "name" : "<div>What is the periodic table?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The <a href=\"https:\/\/www.britannica.com\/topic\/Interactive-Periodic-Table-of-the-Elements\">periodic table<\/a> is a tabular array of the <a href=\"https:\/\/www.britannica.com\/science\/chemical-element\">chemical elements<\/a> organized by <a href=\"https:\/\/www.britannica.com\/science\/atomic-number\">atomic number<\/a>, from the element with the lowest atomic number, <a href=\"https:\/\/www.britannica.com\/science\/hydrogen\">hydrogen<\/a>, to the element with the highest atomic number, <a href=\"https:\/\/www.britannica.com\/science\/element-118\">oganesson<\/a>. The atomic number of an element is the number of <a href=\"https:\/\/www.britannica.com\/science\/proton-subatomic-particle\">protons<\/a> in the nucleus of an <a href=\"https:\/\/www.britannica.com\/science\/atom\">atom<\/a> of that element. Hydrogen has 1 proton, and oganesson has 118." } } , { "@type" : "Question", "name" : "<div>What do periodic table groups have in common?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The groups of the periodic table are displayed as vertical columns numbered from 1 to 18. The <a href=\"https:\/\/www.britannica.com\/science\/chemical-element\">elements<\/a> in a group have very similar chemical properties, which arise from the number of valence electrons present\u2014that is, the number of <a href=\"https:\/\/www.britannica.com\/science\/electron\">electrons<\/a> in the outermost shell of an <a href=\"https:\/\/www.britannica.com\/science\/atom\">atom<\/a>." } } , { "@type" : "Question", "name" : "<div>Where does the periodic table come from?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The arrangement of the <a href=\"https:\/\/www.britannica.com\/science\/chemical-element\">elements<\/a> in the periodic table comes from the electronic configuration of the elements. Because of the <a href=\"https:\/\/www.britannica.com\/science\/Pauli-exclusion-principle\">Pauli exclusion principle<\/a>, no more than two <a href=\"https:\/\/www.britannica.com\/science\/electron\">electrons<\/a> can fill the same orbital. The first row of the periodic table consists of just two elements, <a href=\"https:\/\/www.britannica.com\/science\/hydrogen\">hydrogen<\/a> and <a href=\"https:\/\/www.britannica.com\/science\/helium-chemical-element\">helium<\/a>. As <a href=\"https:\/\/www.britannica.com\/science\/atom\">atoms<\/a> have more electrons, they have more orbits available to fill, and thus the rows contain more elements farther down in the table." } } , { "@type" : "Question", "name" : "<div>Why does the periodic table split?<\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "The <a href=\"https:\/\/www.britannica.com\/topic\/Interactive-Periodic-Table-of-the-Elements\">periodic table<\/a> has two rows at the bottom that are usually split out from the main body of the table. These rows contain <a href=\"https:\/\/www.britannica.com\/science\/chemical-element\">elements<\/a> in the <a href=\"https:\/\/www.britannica.com\/science\/lanthanide\">lanthanoid<\/a> and <a href=\"https:\/\/www.britannica.com\/science\/actinoid-element\">actinoid<\/a> series, usually from 57 to 71 (<a href=\"https:\/\/www.britannica.com\/science\/lanthanum\">lanthanum<\/a> to <a href=\"https:\/\/www.britannica.com\/science\/lutetium\">lutetium<\/a>) and 89 to 103 (<a href=\"https:\/\/www.britannica.com\/science\/actinium\">actinium<\/a> to <a href=\"https:\/\/www.britannica.com\/science\/lawrencium\">lawrencium<\/a>), respectively. There is no scientific reason for this. It is merely done to make the table more compact. " } } ] } </script> <div class="top-questions qa-accordion d-flex flex-column module-spacing"><div class="font-weight-bold font-14 mb-5"> Top Questions </div><div id="intent-accordion" class="md-intent-accordion"><div class="top-question bg-gray-50 rounded" data-value="1"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What is the periodic table?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The <a href="https://www.britannica.com/topic/Interactive-Periodic-Table-of-the-Elements" class="md-crosslink " data-show-preview="true">periodic table</a> is a tabular array of the <a href="https://www.britannica.com/science/chemical-element" class="md-crosslink " data-show-preview="true">chemical elements</a> organized by <a href="https://www.britannica.com/science/atomic-number" class="md-crosslink " data-show-preview="true">atomic number</a>, from the element with the lowest atomic number, <a href="https://www.britannica.com/science/hydrogen" class="md-crosslink " data-show-preview="true">hydrogen</a>, to the element with the highest atomic number, <a href="https://www.britannica.com/science/element-118" class="md-crosslink " data-show-preview="true">oganesson</a>. The atomic number of an element is the number of <a href="https://www.britannica.com/science/proton-subatomic-particle" class="md-crosslink " data-show-preview="true">protons</a> in the nucleus of an <a href="https://www.britannica.com/science/atom" class="md-crosslink " data-show-preview="true">atom</a> of that element. Hydrogen has 1 proton, and oganesson has 118.</p></div></div></div><div class="top-question bg-gray-50 rounded" data-value="2"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What do periodic table groups have in common?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The groups of the periodic table are displayed as vertical columns numbered from 1 to 18. The <a href="https://www.britannica.com/science/chemical-element" class="md-crosslink " data-show-preview="true">elements</a> in a group have very similar chemical properties, which arise from the number of valence electrons present—that is, the number of <a href="https://www.britannica.com/science/electron" class="md-crosslink " data-show-preview="true">electrons</a> in the outermost shell of an <a href="https://www.britannica.com/science/atom" class="md-crosslink " data-show-preview="true">atom</a>.</p></div></div></div><div class="top-question bg-gray-50 rounded" data-value="3"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>Where does the periodic table come from?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The arrangement of the <a href="https://www.britannica.com/science/chemical-element" class="md-crosslink " data-show-preview="true">elements</a> in the periodic table comes from the electronic configuration of the elements. Because of the <a href="https://www.britannica.com/science/Pauli-exclusion-principle" class="md-crosslink " data-show-preview="true">Pauli exclusion principle</a>, no more than two <a href="https://www.britannica.com/science/electron" class="md-crosslink " data-show-preview="true">electrons</a> can fill the same orbital. The first row of the periodic table consists of just two elements, <a href="https://www.britannica.com/science/hydrogen" class="md-crosslink " data-show-preview="true">hydrogen</a> and <a href="https://www.britannica.com/science/helium-chemical-element" class="md-crosslink " data-show-preview="true">helium</a>. As <a href="https://www.britannica.com/science/atom" class="md-crosslink " data-show-preview="true">atoms</a> have more electrons, they have more orbits available to fill, and thus the rows contain more elements farther down in the table.</p></div></div></div><div class="top-question bg-gray-50 rounded" data-value="4"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>Why does the periodic table split?</div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>The <a href="https://www.britannica.com/topic/Interactive-Periodic-Table-of-the-Elements" class="md-crosslink " data-show-preview="true">periodic table</a> has two rows at the bottom that are usually split out from the main body of the table. These rows contain <a href="https://www.britannica.com/science/chemical-element" class="md-crosslink " data-show-preview="true">elements</a> in the <a href="https://www.britannica.com/science/lanthanide" class="md-crosslink " data-show-preview="true">lanthanoid</a> and <a href="https://www.britannica.com/science/actinoid-element" class="md-crosslink " data-show-preview="true">actinoid</a> series, usually from 57 to 71 (<a href="https://www.britannica.com/science/lanthanum" class="md-crosslink " data-show-preview="true">lanthanum</a> to <a href="https://www.britannica.com/science/lutetium" class="md-crosslink " data-show-preview="true">lutetium</a>) and 89 to 103 (<a href="https://www.britannica.com/science/actinium" class="md-crosslink " data-show-preview="true">actinium</a> to <a href="https://www.britannica.com/science/lawrencium" class="md-crosslink " data-show-preview="true">lawrencium</a>), respectively. There is no scientific reason for this. It is merely done to make the table more compact. </p></div></div></div><button class="show-more-button js-toggle-top-questions btn btn-unstyled font-14 d-flex pr-10 rounded-sm"><em class="material-icons" data-icon="expand_more"></em></button></div></div><div class="bg-gray-50 p-15 rounded module-spacing recent-news d-flex flex-column float-false"> <div> <h2 class="font-weight-bold font-14 m-0 d-inline"> News <span class="text-gray-600">•</span> </h2> <div class="recent-news-item first-recent-news-item d-inline"> <a class="font-14 gtm-ap-news-link" href="https://www.livescience.com/chemistry/elements/scientists-just-got-1-step-closer-to-creating-a-superheavy-element-that-is-so-big-it-will-add-a-new-row-to-the-periodic-table" rel="nofollow">Scientists just got 1 step closer to creating a 'superheavy' element that is so big, it will add a new row to the periodic table</a> <span class="font-14 text-gray-600"> <span>•</span> Nov. 7, 2024, 4:59 AM ET (Live Science) </span> </div> </div> <div class="rest-of-recent-news-items"> <button class="js-toggle-recent-news d-flex btn btn-unstyled font-14 pr-10 rounded-sm mt-10" aria-label="Toggle additional news items"> Show less <em class="material-icons" data-icon="expand_less"></em> </button> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref1185987"></span>periodic table</strong>, in <span id="ref621281"></span><a href="https://www.britannica.com/science/chemistry" class="md-crosslink " data-show-preview="true">chemistry</a>, the organized <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="array" href="https://www.britannica.com/dictionary/array" data-type="EB">array</a> of all the <a href="https://www.britannica.com/science/chemical-element" class="md-crosslink " data-show-preview="true">chemical elements</a> in order of increasing <span id="ref1274979"></span><a href="https://www.britannica.com/science/atomic-number" class="md-crosslink " data-show-preview="true">atomic number</a>—i.e., the total number of <a href="https://www.britannica.com/science/proton-subatomic-particle" class="md-crosslink " data-show-preview="true">protons</a> in the atomic nucleus. When the chemical elements are thus arranged, there is a recurring pattern called the “periodic law” in their properties, in which elements in the same column (group) have similar properties. The initial discovery, which was made by <a href="https://www.britannica.com/biography/Dmitri-Mendeleev" class="md-crosslink " data-show-preview="true">Dmitry I. Mendeleev</a> in the mid-19th century, has been of inestimable value in the development of <a href="https://www.britannica.com/science/chemistry" class="md-crosslink " data-show-preview="true">chemistry</a>.</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">It was not actually recognized until the second decade of the 20th century that the order of elements in the periodic system is that of their atomic numbers, the integers of which are equal to the positive electrical charges of the <span id="ref621283"></span><a href="https://www.britannica.com/science/atomic-nucleus" class="md-crosslink ">atomic nuclei</a> expressed in electronic units. In subsequent years great progress was made in explaining the periodic law in terms of the <a href="https://www.britannica.com/science/electronic-configuration" class="md-crosslink autoxref " data-show-preview="true">electronic structure</a> of atoms and molecules. This clarification has increased the value of the law, which is used as much today as it was at the beginning of the 20th century, when it expressed the only known relationship among the elements.</p><span class="marker MOD2 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref80826"> <h2 class="h1">History of the periodic law</h2> <span class="marker PREMOD3 mod-inline"></span><div class="assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100" data-type="other"><div class="slider-container js-slider-container overflow-hidden d-flex"><div class="rw-track d-flex align-items-center"><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="91" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/45/7445-050-BB332C27/version-periodic-table-elements.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/451929/91"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/45/7445-050-BB332C27/version-periodic-table-elements.jpg"><img src="https://cdn.britannica.com/45/7445-050-BB332C27/version-periodic-table-elements.jpg?w=300" alt="periodic table" data-width="2000" data-height="1400" loading="eager"></picture><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">1 of 4</div><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/45/7445-050-BB332C27/version-periodic-table-elements.jpg" data-href="/media/1/451929/91">periodic table</a><span>Modern version of the periodic table of the elements (printable).</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="246857" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="216557"><a data-id="216557" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/How-the-periodic-table-organizes-the-elements/-246857"><img src="https://cdn.britannica.com/57/216557-138-6420551F/How-the-periodic-table-organizes-the-elements.jpg?w=800&h=450&c=crop" alt="Understanding the organization of the periodic table" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/XeDaMiXm.m3u8" } ], "image": "https://cdn.britannica.com/57/216557-138-6420551F/How-the-periodic-table-organizes-the-elements.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/gXm2al7M", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/hcA4H9pP.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">2 of 4</div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="216557">Understanding the organization of the periodic table</span><span>An overview of how the periodic table organizes the elements into columns and rows.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/science/periodic-table/images-videos">See all videos for this article</a></figcaption></figure></div><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="253085" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/13/220013-050-16EC5F2F/periodic-table-atomic-weight.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/451929/253085"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/13/220013-050-16EC5F2F/periodic-table-atomic-weight.jpg"><img src="https://cdn.britannica.com/13/220013-050-16EC5F2F/periodic-table-atomic-weight.jpg?w=300" alt="periodic table with atomic number, symbol, and atomic weight" data-width="2000" data-height="1400" loading="eager"></picture><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">3 of 4</div><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/13/220013-050-16EC5F2F/periodic-table-atomic-weight.jpg" data-href="/media/1/451929/253085">periodic table with atomic number, symbol, and atomic weight</a><span>Periodic table showing each element's atomic number, symbol, and atomic weight.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div><div class="position-relative rw-slide col-100 px-20 "><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="159065" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="151063"><a data-id="151063" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/Explanation-periodic-table/-159065"><img src="https://cdn.britannica.com/63/151063-138-8D2B90F4/Explanation-periodic-table.jpg?w=800&h=450&c=crop" alt="What is the periodic law?" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/McUvbOlF.m3u8" } ], "image": "https://cdn.britannica.com/63/151063-138-8D2B90F4/Explanation-periodic-table.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/QbWmZPla", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/gyADtrma.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div><div class="position-absolute top-10 left-10 assembly-slide-tag rounded-lg">4 of 4</div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="151063">What is the periodic law?</span><span>Explanation of the periodic table.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/science/periodic-table/images-videos">See all videos for this article</a></figcaption></figure></div></div></div><button disabled="true" class="prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_left"></span></button><button disabled="true" class="next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20"><span class="material-icons" data-icon="keyboard_arrow_right"></span></button></div><p class="topic-paragraph">The early years of the 19th century witnessed a rapid development in <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="analytical" href="https://www.merriam-webster.com/dictionary/analytical" data-type="MW">analytical</a> chemistry—the art of distinguishing different chemical substances—and the consequent building up of a vast body of knowledge of the chemical and physical properties of both elements and <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="compounds" href="https://www.merriam-webster.com/dictionary/compounds" data-type="MW">compounds</a>. This rapid expansion of chemical knowledge soon necessitated <span id="ref624390"></span><a href="https://www.britannica.com/science/classification-science" class="md-crosslink ">classification</a>, for on the classification of chemical knowledge are based not only the systematized literature of chemistry but also the laboratory arts by which chemistry is passed on as a living <a href="https://www.britannica.com/science/science" class="md-crosslink autoxref " data-show-preview="true">science</a> from one generation of chemists to another. Relationships were <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="discerned" href="https://www.britannica.com/dictionary/discerned" data-type="EB">discerned</a> more readily among the compounds than among the elements; it thus occurred that the classification of elements lagged many years behind that of compounds. In fact, no general agreement had been reached among chemists as to the classification of elements for nearly half a century after the systems of classification of compounds had become established in general use.</p><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph"><span id="ref621284"></span><a href="https://www.britannica.com/biography/Johann-Wolfgang-Dobereiner" class="md-crosslink " data-show-preview="true">J.W. Döbereiner</a> in 1817 showed that the combining weight, meaning <span id="ref621285"></span><a href="https://www.britannica.com/science/atomic-weight" class="md-crosslink " data-show-preview="true">atomic weight</a>, of <a href="https://www.britannica.com/science/strontium" class="md-crosslink autoxref " data-show-preview="true">strontium</a> lies midway between those of <a href="https://www.britannica.com/science/calcium" class="md-crosslink autoxref " data-show-preview="true">calcium</a> and <a href="https://www.britannica.com/science/barium" class="md-crosslink autoxref " data-show-preview="true">barium</a>, and some years later he showed that other such “<span id="ref621286"></span><a href="https://www.britannica.com/science/triad-chemistry" class="md-crosslink " data-show-preview="true">triads</a>” exist (chlorine, <a href="https://www.britannica.com/science/bromine" class="md-crosslink autoxref " data-show-preview="true">bromine</a>, and <a href="https://www.britannica.com/science/iodine" class="md-crosslink autoxref " data-show-preview="true">iodine</a> [halogens] and <a href="https://www.britannica.com/science/lithium-chemical-element" class="md-crosslink autoxref " data-show-preview="true">lithium</a>, <a href="https://www.britannica.com/science/sodium" class="md-crosslink autoxref " data-show-preview="true">sodium</a>, and <a href="https://www.britannica.com/science/potassium" class="md-crosslink autoxref " data-show-preview="true">potassium</a> [alkali metals]). J.-B.-A. Dumas, L. Gmelin, E. Lenssen, Max von Pettenkofer, and J.P. Cooke expanded Döbereiner’s suggestions between 1827 and 1858 by showing that similar relationships extended further than the <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="triads" href="https://www.britannica.com/dictionary/triads" data-type="EB">triads</a> of elements, <a href="https://www.britannica.com/science/fluorine" class="md-crosslink autoxref " data-show-preview="true">fluorine</a> being added to the halogens and <a href="https://www.britannica.com/science/magnesium" class="md-crosslink autoxref " data-show-preview="true">magnesium</a> to the alkaline-earth metals, while <a href="https://www.britannica.com/science/oxygen" class="md-crosslink autoxref " data-show-preview="true">oxygen</a>, <a href="https://www.britannica.com/science/sulfur" class="md-crosslink autoxref " data-show-preview="true">sulfur</a>, <a href="https://www.britannica.com/science/selenium" class="md-crosslink autoxref " data-show-preview="true">selenium</a>, and <a href="https://www.britannica.com/science/tellurium" class="md-crosslink autoxref " data-show-preview="true">tellurium</a> were classed as one family and <a href="https://www.britannica.com/science/nitrogen" class="md-crosslink autoxref " data-show-preview="true">nitrogen</a>, <a href="https://www.britannica.com/science/phosphorus-chemical-element" class="md-crosslink autoxref " data-show-preview="true">phosphorus</a>, <a href="https://www.britannica.com/science/arsenic" class="md-crosslink autoxref " data-show-preview="true">arsenic</a>, <a href="https://www.britannica.com/science/antimony" class="md-crosslink autoxref " data-show-preview="true">antimony</a>, and <a href="https://www.britannica.com/science/bismuth" class="md-crosslink autoxref " data-show-preview="true">bismuth</a> as another family of elements.</p><span class="marker MOD4 mod-inline"></span> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">Attempts were later made to show that the atomic weights of the elements could be expressed by an <a href="https://www.britannica.com/science/arithmetic-function" class="md-crosslink autoxref " data-show-preview="true">arithmetic function</a>, and in 1862 <span id="ref621287"></span>A.-E.-B. de Chancourtois proposed a classification of the elements based on the new values of atomic weights given by <a href="https://www.britannica.com/biography/Stanislao-Cannizzaro" class="md-crosslink autoxref " data-show-preview="true">Stanislao Cannizzaro’s</a> system of 1858. De Chancourtois plotted the atomic weights on the surface of a cylinder with a circumference of 16 units, corresponding to the approximate atomic weight of oxygen. The resulting helical curve brought closely related elements onto corresponding points above or below one another on the cylinder, and he suggested in consequence that “the properties of the elements are the properties of numbers,” a remarkable prediction in the light of modern knowledge.</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/periodic-table-names-symbols-quiz" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/66/215466-131-16036BD8/Concept-artwork-periodic-table-elements.jpg" alt="Concept artwork on the periodic table of elements." class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">118 Names and Symbols of the Periodic Table Quiz</div> </div> </a><span class="marker MOD5 mod-inline"></span> <section data-level="2" id="ref80827"> <h2 class="h2">Classification of the elements</h2> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">In 1864, <span id="ref621288"></span><a href="https://www.britannica.com/biography/John-Newlands" class="md-crosslink " data-show-preview="true">J.A.R. Newlands</a> proposed classifying the elements in the order of increasing atomic weights, the elements being assigned ordinal numbers from unity upward and divided into seven <span id="ref621289"></span><a href="https://www.britannica.com/science/group-periodic-table" class="md-crosslink " data-show-preview="true">groups</a> having properties closely related to the first seven of the elements then known: <a href="https://www.britannica.com/science/hydrogen" class="md-crosslink autoxref " data-show-preview="true">hydrogen</a>, lithium, <a href="https://www.britannica.com/science/beryllium" class="md-crosslink autoxref " data-show-preview="true">beryllium</a>, <a href="https://www.britannica.com/science/boron-chemical-element" class="md-crosslink autoxref " data-show-preview="true">boron</a>, <a href="https://www.britannica.com/science/carbon-chemical-element" class="md-crosslink autoxref " data-show-preview="true">carbon</a>, nitrogen, and oxygen. This relationship was termed the <span id="ref621290"></span>law of octaves, by <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="analogy" href="https://www.merriam-webster.com/dictionary/analogy" data-type="MW">analogy</a> with the seven intervals of the musical scale.</p><div class="one-good-fact-module"> </div><span class="marker MOD6 mod-inline"></span> <span class="marker PREMOD7 mod-inline"></span><p class="topic-paragraph">Then in 1869, as a result of an extensive correlation of the properties and the atomic weights of the elements, with special attention to <span id="ref621291"></span><a href="https://www.britannica.com/science/valence-chemistry" class="md-crosslink " data-show-preview="true">valency</a> (that is, the number of single bonds the element can form), Mendeleev proposed the periodic law, by which “the elements arranged according to the magnitude of atomic weights show a periodic change of properties.” <span id="ref621292"></span>Lothar Meyer had independently reached a similar conclusion, published after the appearance of Mendeleev’s paper.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; 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Periodic table | Definition, Elements, Groups, Charges, Trends, & Facts | Britannica