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The introduction of atomic structure.
CHEMISTRY - Secondary 2
In This part we will study:
1. Democritus's (Greek philosopher) idea:
He imagined the possibility of dividing any piece of matter to smaller parts, then dividing those parts into smaller particles and so on, until we reach to an undividable fragment, he named it an "atom".

2. Aristotle's idea (4th Century B.C):
• He rejected the former concept of the atom and believed that matter - whatever its nature - is composed of four components, which are water, air, dust and fire.
• It was believed that cheap metals as iron or copper can be changed into precious ones as gold by changing the ratios of these four constituents.
• This illogical idea caused a retard of development in chemistry science for more than thousand years, because the scientists were busy by trying to change cheap metals into precious ones.
3. Boyle's idea (1661):
The Irish scientist Boyle refused Aristotle's idea about the nature of matter and gave the first definition of the element.
Element
It is a pure simple substance that can't be changed to simpler forms by the traditional chemical methods.

4. Dalton's model of the atom (1803):
English scientist John Dalton stated the first theory about the atomic structure.
The main postulates of Dalton's atomic theory
1. The element is composed of very small particles, which are named atoms.
2. The atom is a very minute undividable solid particle.
3.Masses of atoms of the same element are similar, but differ from one element to another.
4. The compounds are formed by the combination of atoms of different elements in simple numerical ratios.
5.This last postulate is known as the law of constant proportion which states that each compound always contains the same elements in the same proportion (by mass) no matter how different the method of its preparation.

Best wishes to you
Mr.Ahmed Elbasha

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