Discovery of Cathode rays(Electron) and properties||Atomic structure||Chemistry||class 11

         Atom:-An atom is the smallest particle of element having all the chemical properties of the element does not exist in free state and takes part in chemical reaction.

An atom consists of three fundamental particle like electron proton neutron.

Discovery of Cathode rays (election)

J.J.Thomsos in 1897 applied a high potential difference (about 10,000 volt) throught gases at very low pressure(10^-2atm pressure) between two oppositely charged electrodes i.e cathode and anode in an electric discharge tube and observed that some invisible rays were emitted from cathode and hence these rays were called cathode rays.

Cathode rays were found to consist of flow of negatively charged particles which were called ''electron''.

The name electron was given by "Stoney".

Cathode rays are nothing but flow of electrons further investigation were made by many other scientists such as Willium croocks, J.Perrin, Julius plucker and others.

Properties of Cathode rays

1-Cathode rays are invisible.

2-They travel in a straight line with very high speed ranging the velocity 10⁹ to 10¹¹ cm/s.

3-Cathode rays consist of flow of negatively charged particles, called 'electron'.

4-They have kinetic energy.

5- They have penetrating power.

6-They ionize the neutral gas when passed throught it.

7- They produce fluorescence when bombarded on zinc Sulphide (ZnS) screen.

8- The properties of cathode rays are independent to the properties of the gases are properties of electrodes used in discharge tube.

9- When cathode rays were passed between two oppositely charged plate these were defllected towards a positively charged plate indicating that cathode rays consist of flow of negatively charged particles.

10- The (e/m ratio) or charge/mass ratio of electron was established by J.J.Thomson equal to 1.76×10⁸ coulomb/gram.

11- The relative charge of electron is -1(e-)

12- The absolute charge of an electron=-1.602×10^-19 coulomb (SI)

     = -4.8×10^-10 esu (C.G.S)

The absolute charge of electron was determined by "Mullikn" by oil drop experiment.

13- Charge of 1mole electron= (6.022×10²³)×(1.602×10^-19col)

=>96500 coulomb (1F)

=> 1Faraday.

14- The relative mass of an electron is 1/1837th of mass of one atom of hydrogen i.e equal to 0.0005486 amu= 0 amu

15- The absolute mass of one electron is 9.11×10^-31 kg or 9.11×10^-23g

16- The mass of 1 mole electron is

=> (6.022×10²³)×(9.11×10^-28g)

=>54.8×10^-5g

=> 5.48×10^-4 g

17- An electron may be defined as the fundamental particle of an atom carrying unit negative charge (-1) and having the mass equal to 9.11×10^-31 kg.