|  | Public Health Safety | Public Health

Periodic Table Definitions

The periodic classification of elements is one of the most significant classifications in science, since it summarizes the facts of inorganic chemistry in a tabular form and serves as a key to the world of inorganic chemistry. It was only in the hands of the Russian chemist Mendeleyev in 1864 that periodic classification of elements crystallized into a logical pattern. Mendeleyev arranged all the elements in order of increasing atomic weights, and found that elements that are chemically similar to each other, occur at regular intervals and that identical properties recur periodically throughout the series.

  1. Long and Short Periodic Table

    • Mendeleyev organized the natural elements in two different tabular forms, distinguished as "long and short periodic tables." In the long periodic table, the elements with similar chemical properties are placed under one another in the same vertical column, or group. In the short periodic table, all elements of more or less similar characteristics, having the same normal valency (i.e. a property of atoms), are placed in the same vertical group.

    Groups

    • The vertical columns of the periodic table are called groups, or families, or simply columns. There are altogether 18 vertical columns in the long periodic table. In terms of the electronic configurations of the atoms of the elements, a group consists of those elements whose atoms are identical in their outer-most electronic configuration.

    Periods

    • The horizontal rows of the periodic table are called periods. There are seven periods in all. In each period, the elements have been placed in the increasing order of their atomic number. The first element of each period is on alkali metal and the last element is a noble gas.

    Significance of the Periodic Table

    • The periodic table of elements shaped the destiny of chemistry to a great extent. It was the first natural classification of elements and it proved to be a powerful tool for scientific research. At the time, Mendeleyev constructed the periodic table many elements were unknown. Mendeleyev left several vacant positions to fit in those elements. However, he predicted the physical and chemical properties of each of these missing elements, which agreed remarkably well with those actually observed when these elements were subsequently discovered.

    Defects of Mendeleyev's Periodic Table

    • Mendeleyev has placed hydrogen in group IA, along with alkali metals, but at the same time, hydrogen also resembles halogens. Thus, the position of hydrogen is still a matter of dispute.

      Many pairs of elements, which have dissimilar properties, have been placed in the same groups, for examples, Cu (IB)-Hg (IIB), and Ag (IB)-TI (IIIA).

Public Health - Related Articles