Chemistry - The Periodic Table

As shown from the image in the previous post, a Periodic table is a brilliant way of arranging elements. They are put in order of their proton numbers.

The horizontal row of elements is called a PERIOD. Each PERIOD is numbered 1,2,3 etc.

The Vertical set of elements is called a GROUP.The groups are numbered from I to VII and then Group 0 (or group VII)
Group I = Alkali metals
Group II = Alkaline earth metals
Group VII = Halogens
Group 0 = Noble Gases

The elements between Group I and III are all metals. They are called the transiton elements.

The Importance of the Periodic Table:
The arrangement of the elements in the Periodic table helps us to remember and understand them better. Some patterns are shown here. For example, each vertical group contains elements with similar properties. In addition, propertiess of some elemtns in a group or period, we can make predictions about other elements. This is important because scientific knowledge is only useful if it can predict new facts rather than just explain known facts. For example, caesium, Cs, is in Group I and thus it can be predicted from other Group I metals such as sodium and potassium.

A little Background:
The most successful Periodic Table in the 19th Century was published in 1869 by Dimitri Mendeleev, a Russion chemist, He took the 69 elements and arranged them in order of relative atomic mass. Elements of the same properties were placed in the same vertical columns. Mendeleev also left some gaps for elements that have not been discovered.



In the modern day, there have been many changes made to Mendeleev's Periodic Table.
The modern table includes 46 more elements and all the elements are now arranged in order of proton number.