Evolution concept of the atomic structure , Atomic theory & Properties of cathode rays

From Online Sciences - November 27, 2017

Long time ago man was asking about the nature of matter and its structure , while the trials done by the scientists to answer this question across different eras , the concept of the atomic structure is evolved , The scientists were interested in studying the atomic structure such as Heisenberg , Pauli , Schrodinger , Bohr , De Broglie , Einstein & Planck .

Democrituss ( 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 , In the Greek language : A means no and tom means divide .

Aristotles idea ( 4th century B.C )

He rejected the concept of the atom and believed that all matterwhatever their natureare 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 miserable idea caused a retard of development in chemistry science for more than thousand years because the scientists were busy by changing cheap metals into precious ones .

Boyles idea ( 1661 )

The Irish scientist Boyle refused Aristotles idea about the name of substance and gave the first definition of the element , The element is a pure simple substance that can not be changed to simpler forms by the traditional chemical methods .

Daltons model of the atom ( 1803 )

The English scientist John Dalton stated the first theory about the atomic structure .

The main postulates of Daltons atomic theory :

Thomsons model of the atom ( 1897 )

The scientist Thomson carried out many experiments on the electric discharge through gases from which he had discovered the cathode rays .

Discovery of cathode rays :

It was known that gases do not conduct electricity under normal conditions of pressure and temperature , However , gases conduct electricity in a discharge tube whose two poles are connected to an electric source of a suitable high potential difference and under a very low pressure .

If the potential difference between the two poles of the vacuum glass tube exceeds 10000 volts , a steam of invisible rays was emitted from the cathode ( the negative pole ) , causing a fluorescent glow on hitting the tube wall , These rays were named by cathode rays .

Cathode rays : A stream of invisible rays was emitted from cathode , causing a fluorescent glow hitting the discharge tube wall under very low pressure and potential difference of about 10000 volts , It was later known that they are composed of minute particles named electrons .

Properties of cathode rays

In the light of the electrical discharge experiment , Thomson suggested a new atomic model for the atom .

The postulate of Thomsons model :

Rutherfords model of the atom ( 1911 )

The postulates of Rutherfords atomic theory :


Continue reading at Online Sciences »