Description of the Periodic Table
The periodic table is a detailed index of the elements known to mankind. The most elegant feature of this table is its grouping and organization of elements which neatly places them according to atomic number and group. The periodic table was created to demonstrate the "periods" observed in elements.
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History
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The credit for the invention of the periodic table goes to Dmitri Mendeleev in 1869, although other elemental tables have predated it. This table was made to show certain tendencies within the elements and was organized in such a way that it visually represents such "periodic" trends. As of 2009, the periodic table contains 117 elements. Some of these elements were created synthetically by particle accelerators, while 94 of them are found naturally on Earth.
Organization
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The periodic table is organized mostly in a grid-like fashion of periods (rows) and groups (columns). The more important is groups, in which you can observe a general pattern of similar characteristics of each element contained within each group. For example, all the noble gases (helium, neon, argon and others) are all in the same column. Each element in the table is listed consecutively by atomic number. The atomic number represents the amount of protons in the nucleus of an atom of a particular element.
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Why Mendeleev's Table was Chosen
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There were a number of elemental tables throughout history, but only one became widely accepted even to this day. Dmitri Mendeleev's periodic table best illustrated all the elements with their chemical properties. However, it was not only this that made him successful. His table left room for elements that were not yet discovered. The periodic table of elements is an amendable table that does not need to be completely revamped upon the discovery of a new element. This scalability made it a model for elemental listing since 1869.
Periods
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The rows in the periodic table are known as periods. Their importance is dwarfed by the importance of groups, although periods still have some ground on how the periodic table is constructed. A new period occurs after each noble gas. The importance of periods starts occurring near the bottom of the table, when the lanthanoids and actinoids begin to appear, since most of them have similar properties. This part of the table is separated from the rest of to preserve its composition.
Reactivity in Groups
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The elemental groups in the periodic table show us more than just chemical properties of each element. Each group displays elements that are also of the same reactive tendency. In other words, each element is placed in the periodic table according to how reactive they will be. Alkali metals and halogens tend to be most reactive because they have only one electron, or are missing an electron, in their outermost shell. The noble gases at the last group on the periodic table are the most non-reactive since they have a full set of electrons in their outermost shell.
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