periodic table

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Periodic table with atomic number, symbol, and atomic weight

Understanding the Organization of the Periodic Table

Electronegativity values of the elements in the periodic table

Periodic table with electron configurations

Periodic table with column indicating subshells

Periodic table showing the valence shells

Periodic table with room-temperature state

For Students

periodic table summary

periodic table

Q: 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.

Q: 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.

Q: 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 .

Q: 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.

Q: 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.

Q: Who created the periodic table?

The periodic table was created in 1869 and revised in 1871 by Russian chemist Dmitri Mendeleev , who placed elements in columns according to their chemical properties. From the table, Mendeleev predicted the existence and properties of three elements that had not yet been discovered: scandium , gallium , and germanium .

Q: 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.

chemistry

Also known as: periodic table of the elements

Written by

Linus C. PaulingAll

Fact-checked by

Britannica Editors

Last updated

Dec. 22, 2025 •History

What is the periodic table?

How many elements are on the periodic table?

What do periodic table groups have in common?

Where does the periodic table come from?

How is the periodic table organized?

Who created the periodic table?

Why does the periodic table split?

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

Key People:: Dmitri Mendeleev; Lothar Meyer; Paul-Émile Lecoq de Boisbaudran

Related Topics:: atom; When Was the Periodic Table Invented?; group; period; periodic law

On the Web:: Chemistry LibreTexts - The Periodic Table (Dec. 10, 2025)

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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.