The Origin or History of Periodic Table.

The origin of periodic table. 

  The periodic table shows a systematic arrangement of elements in increasing order of their atomic numbers with elements with similar chemical properties being placed in the same vertical column.

  The following are scientists who contributed to the periodic table:

1. In 1815, Prouts hypothesis was that all elements were made from a whole number of hydrogen atoms.

2. In 1829, Dobereiner drew attention to the fact that there are some groups of three elements with similar chemical properties occur in such a way that the middle member of the elements has a relative atomic mass that is the Arithmetic mean of the other two. He called such groups of elements "TRIADS".
For example, Lithium(7),Sodium(23), Potassium (39.2),He meant to get the atomic mass of sodium you find the mean of Lithium and Potassium, i.e 7+39.2/2 =46.2/2=23.1
He also commented that the difference between the value is nearly 16.

3. In 1858, Cannizaro assigned valencies to atoms as a measure of combining power.

4. In 1864,Newlands noticed that when elements are arranged in increasing relative atomic mass similar properties occurred in every eight element. This is the "Law of Octaves".

5. In 1869, Dimitri Mendeleef(v) a Russian Chemist gave the modern periodic law which states that the properties of the element are a periodic function of their atomic numbers.
He also classified elements into eight(8) groups, namely:
Group 1: Alkali metals
Group 2: Alkaline earth metals

Group 3: Boron family
Group 4: Carbon family
Group 5: Nitrogen family
Group 6: Oxygen family
Group 7: Halogens
Group 8: Noble gases, inert or stable gases.

Besides the eight main groups, there are also the transition groups of elements. These lie between group 2 and 3 in the periodic table.
Horizontal rows in periodic table are called "PERIODS" while the vertical are called "GROUPS".
Among the elements in period 6 and 7 are the elements of Lanthanide and Actinide series respectively. They are also known as inner transition elements.

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