The idea of the smallest matter was proposed by several great people such as the Maharshi kannada as anu and paramanu .Later Democritus a well known Greek philosopher told that matter consists of smallest particle as atom DALTONS ATOMIC THEORY Matter is composed of the smallest particles called as atoms which cannot be further divided Atoms of the same element are alike and behave in the same way in all respects Atoms of different elements are different from each other in all respects. Atoms of either same or different elements combine with each other and give new particles . These are as compound atoms Atom is the only particle which participates in chemical reaction.

JOHN DALTON

J.J Thomson is a great scientist who invented the cathode rays and they contain negative charged particles he also explained that atom is a structure like this and he named that it is a Plum pudding model: J.J.Thomson:

The cathode rays properties are they travel in straight lines , they deflects towards anode when an electric field is applied, they in the presence of magnetic field , they create shadows and mechanical motion. Then the invention cathode rays is done in discharge tube which is invented by William crooks in in 1878

The discharge tube is a glass tube in which the it is equipped with a out let and at the two ends cathode and anode is present with high voltage.

This is a great invention in which the anode rays are also invented by the great scientist named Goldstein :

Its properties are opposite to the properties of cathode rays anode rays consists of the particles of positive charge

This negative charged particles are named as electrons by G.J.Stoney and positive charged particles as protons by Goldstein himself.

After these conclusions we are able to know that matter consists of smallest particles known as atoms and it consists of electrons and protons Suprisingly during that period James Chadwick invented that atom does not only consists of electrons and protons but also a neutral charged particle named Neutron

James Chadwick:

Further experiments proved that there are several 100 sub-atomic particles

We know that atomic model means systematic arrangement of electrons and protons and neutrons

Sub atomic particle10

symbol

Relative charge

Relative mass

Charge in coulomb Mass in a.m.u

Electron e -1 1/1837 1.602*1/10*10*10*___(19) in negative charge

0.00055

Proton p +1 1 unit mass of hydrogen

1.602*1/10*10*10*___(19) in positive charge

1.0073

Neutron n 0 1 unit 0 1.0087

The atomic model expressed by the J.J.Thomson but he did not explained the how the positively and negative charged particles are shielded with out getting neutralised . Discovery of Madam curie helped us in many ways it also took part in this Earnest Rutherford once conducted the alpha scattering experiment its structure is like this . Rutherfo

rd

From this experiment he concluded atomic model like this

From the above experiment he concluded that atom contains protons and neutrons at its center in nucleus and electrons revolve around the nucleus ,remaining space is filled with empty space. As the alpha ray particles hit the atoms in the gold foil the rays which hits nucleus are deviated at different angels , the rays which passes through the empty space passes straightly , which strikes the nucleus at its centre accurately are reflected back wards in which they arrive

This results in the name of planetary atomic model . In this electrons are compared with planets and nucleus with sun

But he did not explained that what forces made electrons revolve around them and comparision electrons and nucleus with planets and sun respectively this is claimed by a scientist named Neilsbhor

Neilsbhor:

Do you know the sum of mass of the number of protons and neutrons is called atomic mass and denoted by (A) . And number of protons and electron are equal to (Z). And number of neutrons are equal to (A-Z). This was given by a scientist named Mosley.