Periodic Table of Elements
The periodic table of elements is a table which shows the arrangement of chemical elements ordered by atomic numbers in columns and rows. It was invented by Russian chemist Dmitri Mendeleev in 1869 to determine the periodic trends in the properties of elements.
The elements are listed according to their increasing atomic numbers. Rows are arranged in such a way that elements with similar properties fall into the same vertical columns. The groups or columns are numbered 1-18. The arrangement is Group 1(alkali metals), Group 2(alkaline earth metals), Group 15 (pnicogens), Group 16(chalcogens), Group 17(halogens) and Group 18(noble gases). There are some groups that enjoy non-systematic names as well. Not only are the groups in the periodic table, some other groupings of elements often named as well. They are lanthanoids and actinoids.
In 2006, the periodic table contained 117 periodic elements. Out of these, 92 are found naturally on earth, and the rest are artificial elements.
Structure of a Periodic Table
To arrange elements in a periodic table, the chemical properties with the electron configuration of an element is determined. The total number of electrons present in an element determines to which period it belongs. The orbital where the electrons reside, determine the block to which it belongs. And the number of valence shell electrons determines the group or family to which it belongs.
The elements with the same number of valence electrons or outer shell electrons are grouped together. As we progress from the lightest element to the heaviest element, the outer shell electrons or the valence, are all in the same type of orbital, with the same shape.
Groups and Periods
The vertical columns in the periodic table are known as the group, and are the most important method of classifying elements. Elements with very similar properties are grouped together and they are names according to the trend in properties, like alkali metals, alkali earth metals, halogens and noble gases.
The horizontal row in the periodic table is known as the period. This is also a type of classification of elements where the horizontal trends and similarities in properties are more significant than vertical trends.
Although Dmitri Mendeleev is the person responsible for creating the proper periodic table, there are other scientists as well who have contributed to its development. In Mendeleev's original table, each period was of the same length. But modern periodic table of elements have longer periods down the table and group the elements into s-, p-, d- and f- blocks to help us understand better.
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