DALTON'S ATOMIC THEORY. டால்டனின்‌அணு‌ கோட்பாடு

DOLTON'S ATOMIC THEORY

Jhon Dalton's ,an English chemist, introduced the first atomic theory known as the Dalton's Atomic Theory in 1808. His theory consists of the points, lso called the petulares of Dalen) Atomic Theory. They are

Atomic theory in 1808 . His theory consists of the points ,also called the postulated of Dalton's Atomic Theory. They are

Allmatter consists of ll indivisible particles called atoms

All atoms of a given element are identical in mass and chemical properties

Atoms of the same element are identical that is, they have same properties, such a mass, size, shape and density. However, atoms of was different elements have different properties .

Atoms of elements  combine to form different compounds with definite properties.

compounds with definite properties. Atoms of an element can combine with the atoms of another element in simple whole He numbers to form molecules of compounds These compounds formed have different properties than the constituent elements. · Atoms are the smallest unit of a substance

that take part in any chemical reaction. · Atoms can neither be created nor destroyed in a chemical reaction. They can only be rearranged.

The smallest atom is the hydrogen atom with one proton and one electron. On the other hand, the largest atom is cesium

Atoms were first thought to be the smallest indivisible particles of matter. But, in late 19th century, it was proved that an atom contains small subatomic particles called protons, electrons and neutrons.

During late 19th century and early 20th century, a number of experiments were conducted which showed that an atom is a divisible unit. The O REDMI NOTE 8 Coming eridA tx MerA atom is made are positively charged subatomic particles calle protons electrically neutral subatomic particle called neutrons and the negatively cha subatomic particles called electrons.

Discovery of Electrons 

The electronS are represented (e-) Electrons were first observed by William Cork British scientist in 1878 by conduction discharge tube experiment. The discharged a glass tube (sealed at both ends) which partially evacuated to maintain a low pre (0.01 mm of mercury) inside the tube. He annl high electric voltage (10,000 volts) between the two electrodes placed at either end of the o found that rays were coming out from negatively charged electrode which was ci cathode. These rays were named cathode rays.

Later, J. J. Thomson in 1897, while studying the properties of cathode rays, discovered that these rays consist of negatively charged particles which are now called electrons. He constructed the same discharge tube experiment and applied an electric field between the path of the cathode rays. He saw that cathode rays were moving towards the positively charged plate of the electric field. He also saw that when magnetic field was applied in the path of the cathode rays, they again changed the direction towards the positive charge. Hence, this proved that cathode rays were negatively - charged particles known as electrons.