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The periodic table, also known as Mendeleev's table, is a table of the chemical elements existing on Earth. The Russian chemist Dmitri Mendeleev is credited with its creation in 1869, although less extensive tables existed before this. He intended to display the patterns apparent in the chemical properties of each element. Since its original creation, new elements have been discovered and added to Mendeleev's initial table.
The structure of the periodic table is very significant. The current table holds 117 elements in a very distinct order for the purpose of showing similarities and differences in chemical properties. Out of all of the elements, 94 are found in nature and the other 24 were synthetically produced with particle accelerators. As well, most copies of the periodic table separate the metal and non-metal elements with a dark stair-step line. The metals are on the left and the non-metals on the right. Additionally, elements are placed in order of increasing atomic number, which is the number of protons in the nucleus of the element's atom. The rows are also organized so that elements with similar properties are found in the same columns. Within each element square, information on the element's symbol, atomic number, atomic mass, electronegativity, electron configuration, and valence numbers can be found. At the bottom of the periodic table is a two row block of elements that contain the lanthanoids and actinides. These groups are classified as inner transitional metals.
The chemical elements classified into groups, periods, and blocks. Groups, also referred to as a families, are the vertical columns located on the periodic table. Groups are considered to be the most significant form of classification. Many groups contain elements with very similar properties and are referred to with special names such as the halogens and alkaline earth metals. Periods are made up of the horizontal rows of the table. Just as groups contain specific trends in similar properties, so do periods. For instance, the d-block contains a row of transition metals. Blocks are important as different regions of the periodic table due to the outer shell of elections within the elements' atoms. Blocks are oriented based on this outer shell. The blocks of the periodic table include the s-block, p-block, d-block, and f-block. Other groupings include poor metals, transitional metals, metalloids, and the platinum group.
The location of elements on the periodic table is extremely important due to the trends of chemical properties in groups and rows. Properties of an element can actually be predicted based on its table location. It is important to remember that trends operate differently when moving vertically and horizontally along the table. Trends within groups are explained by common electron configuration in their valence shells. This also creates likenesses in atomic radius, electronegativity, and ionization energy. From the top of the group to the bottom, atomic radii of the elements increase. Likewise, ionization energy and electronegativity decrease due to electron configuration. Periods also possess similar trends in electronegativity, ionization energy, atomic radii, as well as electron affinity. Moving from the left of the periodic table to the right, atomic radii decreases which causes the ionization energy to increase. As well, moving left to right, electronegativity and electron affinity increase.
Periodic Table: a clickable table with extensive information on each element.
Periodic Table of Chemical Elements: an interactive resource for learning about individual elements.
Periodic Table: an interactive table with a biography of Dmitri Mendeleev.
Electrons and the Periodic Table: a resource on the importance of electron configuration and periodic trends.
Enhanced NMR Periodic Table: another interactive table with clickable elements from Texas A&M University.