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Atom has a very small mass. The method of determining the relative atomic mass stated by Berzelius (1814) from Sweden and P. Dulong and A. Petit (1819), both from France. Berzelius and Dulong and Petit determine the relative atomic mass of the element based on specific heat. The relative atomic mass of an element essential nature and a specific nature, as each element has a specific relative atomic mass different from the other elements.

1.1.   Based on metal characteristic, elements divided become metal and nonmetal.


The elements classified asmetals and as


1.2.Triade Dobereiner



In 1829, Johan Wolfgang Dobereiner, a professor of chemistry in Germany, suggests that the relative atomic mass of Strontium is very close to the average mass of the two other elements like Litium, Natrium and Kalium that. Dobereiner also found some other elements such groups. Therefore, Dobereiner conclude that the elements can be grouped into groups called “Triade tiga unsur”. But unfortunately, Dobereiner failed to show enough triade so useful rule. Although the idea of ​​Dobereiner  not very successful, but it is the first at tempt in the classification of the element. The theory of Dobereiner, example :


Atomic mass

Atomic mass in the middle











Atomic mass Na    =    Atomic mass Li + Atomic mass K


                   =    6,94  +  39,10     =    23,02


1.3.Newlands law of octaves

In 1864 a British chemist named AR Newlands announced the discovery of the so-called Law of Octaves. Newlands arrange the elements of increasing relative atomic mass. Ex. law of octaves Newland is as follows:

Element Atomic number
Li 1
Be 2
B 3
C 4
N 5
O 6
F 7
Na 8
Mg 9
Al 10
Si 11
P 12
Cl 13
K 14
Ca 15
Newlands law of octaves proved valid only for light elements, roughly up to calcium (Ar=40). If passed, similar properties proved too forced.
1.4.Mendeleev Periodic System     
In 1869 a Russian scholar named Dmitri Ivanovich Mendeleev, based on observations of 63 elements known at the time, concluded that the properties of elements are a periodic function of the relative atomic mass. That is, if the elements are arranged according to their relative atomic mass increases, the specific properties will be repeated periodically. Mendeleev placed elements that have similar properties in a single vertical column, called Group. Rows of horizontal, ie lane elements of increasing relative atomic mass, called the period.
1.5.Modern Periodic System of Henry G.Moseley
In the early 20th century, our knowledge of the atom has developed very basic. The experts found that the atom is not something that is not divided but a particle composed of smaller particles called elementary particles or subatomic particles. Atom is now believed to consist of three types of elementary particles, ie protons, electrons, and neutrons. For now we need to mention that the number of protons is characteristic of the element, meaning that each element has a specific number of protons different from other elements. The number of protons in an atom is called the atomic number.

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