Periodic table

Periodic table

The Periodic table is a tabular arrangement of chemical elements, organized based on their atomic number, electron configuration, and recurring chemical properties. Elements are listed in order of increasing atomic number, which corresponds to the number of protons in an element's atomic nucleus. The table has rows called periods and columns called groups.

History

The first periodic table was developed in 1869 by Dmitri Mendeleev. Mendeleev's table was similar to the modern periodic table, but it had some differences. For example, it did not include the noble gases, which were discovered later.

Structure

The periodic table is divided into several blocks:

• The s-block includes the first two groups (alkali metals and alkaline earth metals) as well as hydrogen and helium.
• The p-block includes the last six groups, which contain the metalloids, nonmetals, and the post-transition metals.
• The d-block includes the transition metals.
• The f-block includes the lanthanides and the actinides.

Periods and groups

The periodic table has seven periods. Each period corresponds to the filling of a different electron shell. The groups of the periodic table represent elements with the same electron configuration in their outer shell, which gives them similar chemical properties.

Chemical properties

The periodic table is a powerful tool for predicting the chemical properties of elements. For example, elements in the same group have similar chemical properties because they have the same number of valence electrons.

See also

• History of the periodic table
• Electron configuration
• Chemical element
• Dmitri Mendeleev

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