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

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• Introduction & Top Questions
• The periodic table
  • Periods
  • Groups
    • Classification of elements into groups
    • Periodic trends in properties
• The basis of the periodic system
  • Electronic structure
  • Periodicity of properties of the elements
• Other chemical and physical classifications
• History of the periodic law
  • Classification of the elements
    • The first periodic table
    • Other versions of the periodic table
  • Predictive value of the periodic law
    • Discovery of new elements
    • Significance of atomic numbers
    • Elucidation of the periodic law

References & Edit History Quick Facts & Related Topics Images, Videos & Interactives At a Glance periodic table summary Quizzes 118 Names and Symbols of the Periodic Table Quiz Facts You Should Know: The Periodic Table Quiz Science Quiz Periodic Table of the Elements 36 Questions from Britannica’s Most Popular Science Quizzes Related Questions

• What is the periodic table?
• Where does the periodic table come from?
• How is the periodic table organized?
• When did Dmitri Mendeleev present the first periodic table?
• Why does the periodic table split?

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periodic table chemistry Ask Anything Quick Summary Homework Help Also known as: periodic table of the elements Written by Linus C. Pauling 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... Linus C. PaulingAll Fact-checked by Britannica Editors 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.... Britannica Editors Last updated Feb. 13, 2026 •History Britannica AI Ask Anything Quick Summary Table of Contents Table of Contents Quick Summary Ask Anything Top Questions

What is the periodic table?

The periodic table is a tabular array of the chemical elements organized by atomic number, from the element with the lowest atomic number, hydrogen, to the element with the highest atomic number, oganesson. The atomic number of an element is the number of protons in the nucleus of an atom of that element. Hydrogen has 1 proton, and oganesson has 118.

How many elements are on the periodic table?

There are 118 elements on the periodic table. The elements are arranged in order of increasing atomic number, which is the number of protons in that atom’s nucleus. Hydrogen, the element with the lowest atomic number, has 1 proton; oganesson, the element with the highest atomic number, has 118.

What do periodic table groups have in common?

The groups of the periodic table are displayed as vertical columns numbered from 1 to 18. The elements in a group have very similar chemical properties, which arise from the number of valence electrons present—that is, the number of electrons in the outermost shell of an atom.

Where does the periodic table come from?

The periodic table came from chemists in the 19th century realizing that elements could be grouped together based on their properties. In 1869 Russian chemist Dmitri Mendeleev grouped the known elements into a table with 17 columns. He revised his table in 1871 and was able to predict the existence of new elements as well as show that the atomic weights for some elements were inaccurate.

How is the periodic table organized?

The arrangement of the elements in the periodic table comes from the electronic configuration of the elements. Because of the Pauli exclusion principle, no more than two electrons can fill the same orbital. The first row of the periodic table consists of just two elements, hydrogen and helium. As atoms have more electrons, they have more orbits available to fill, and thus the rows contain more elements farther down in the table.

When did Dmitri Mendeleev present the first periodic table?

The first periodic table was presented on March 6, 1869, and revised in 1871 by Russian chemist Dmitri Mendeleev, who placed elements in columns according to their chemical properties. Based on the periodic law that guided the arrangement of the table, Mendeleev predicted the existence and properties of three elements that had not yet been discovered: scandium, gallium, and germanium.

Why does the periodic table split?

The periodic table has two rows at the bottom that are usually split out from the main body of the table. These rows contain elements in the lanthanoid and actinoid series, usually from 57 to 71 (lanthanum to lutetium) and 89 to 103 (actinium to lawrencium), respectively. There is no scientific reason for this. It is done merely to make the table more compact for display.

periodic table, in chemistry, the organized array of all the chemical elements in order of increasing atomic number—i.e., the total number of protons 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 of this pattern by Dmitri I. Mendeleev in the mid-19th century has been of inestimable value in the development of chemistry.

In full: periodic table of the elements (Show more) Key People: Dmitri Mendeleev Lothar Meyer Paul-Émile Lecoq de Boisbaudran (Show more) Related Topics: atom When Was the Periodic Table Invented? group periodic law period (Show more) On the Web: ABC listen - Nightlife - The Fascinating History of the Periodic Table (Feb. 06, 2026) (Show more) See all related content

It was not recognized until the 1910s that the order of elements in the periodic system is that of their atomic numbers, which are equal to the positive electrical charges of the atomic nuclei expressed in electronic units. In subsequent years great progress was made in explaining the periodic law in terms of the electronic structure 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.