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The periodic table, also called the periodic table of elements, is an organized arrangement of the 118 known chemical elements. The chemical elements are arranged from left to right and top to bottom in order of increasing atomic number, or the number of protons in an atom 's nucleus, which generally coincides with increasing atomic mass.

The horizontal rows on the periodic table are called periods, where each period number indicates the number of orbitals for the elements in that row, according to Los Alamos National Laboratory . (Atoms have protons and neutrons in their nucleus, and surrounding that, they have their electrons arranged in orbitals, where an atomic orbital is a math term that describes the location of an electron as well as its wave-like behavior.)

For instance, period 1 includes elements that have one atomic orbital where electrons spin; period 2 has two atomic orbitals, period 3 has three and so on up to period 7. The columns, or groups, on the periodic table represent the atomic elements that have the same number of valence electrons, or those electrons in the outermost orbital shell. As an example, elements in Group 8A (or VIIIA) all have a full set of eight electrons in the highest-energy orbital, according to chemist William Reusch, on his webpage at Michigan State University. Elements that occupy the same column on the periodic table (called a "group") have identical valence electron configurations and consequently behave in a similar fashion chemically. For instance, all the group 18 elements are inert gases, meaning they don't react with any other elements.

Related: How are the elements grouped?

Who created the periodic table?

Dmitri Mendeleev, a Russian chemist and inventor, is considered the "father" of the periodic table, according to the Royal Society of Chemistry. In the 1860s, Mendeleev was a popular lecturer at a university in St. Petersburg, Russia. At the time, no modern…

Tim Sharp

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