The particles that carry on electric charge are called charged particles.

These are on, rubbing two objects together,

electrons and they became electrically charged.

protons

   Upto 1900 → Atom was indivisible

      JJ Thomson → • British Physicist

                             • Born (18 Dec. 1856)

                             • Nobel prize in Physics → 1906

  is 2000 times less Because of the discovery of electrons

      then the mass

        of proton or

       negligible

 When electric current was passed through gas at low pressure and at high voltage, Some rays were limited emitted through cathode and were travelling towards Anode called cathode rays consisting of negatively charged particles called electrons.

Discovery of proton * Mass of proton = 1.6 x 10-27 kg

E. Goldstein discovered the proton and they also discovered of canal or anode rays

positively charged radiation

Thomson's Model of An atom (Plum pudding model)

 Atom is positively charged sphere in which electrons are present at

 certain places like seeds in watermelon or pumbs in a pudding.

          Drawbacks:

         (i) His model could not explain the

               stability of an atom

         (ii) And also the distribution of

                charges

(i) Atom consists of a positively charged sphere and the electrons are

   embedded in it

(ii) Both charges are equal in magnitude. so, the atom as a whole is

  electrically neutral.

 Rutherford is the father of nuclear Physics Nobel prize in 1908

 To understand the structure of atom Rutherford perform the experiment as scattering experiment.

 Scattering experiment => He took gold foil and passed alpha rays through it. Alpha rays are actually positively charged rays consisting of Helium nucleus (He).

 i. Maximum rays passed straight

 ii. Some rays were deflected through small and large angles.

 iii. Some rays rebounded.

 i. Most of the space in atom is empty

 ii. There is something in centre of the atom

   called Nucleus, that is positively charged.

 Drawback

(i) Rutherford's model of atom does not explain the Stability of the

  atom.

➡ According to the electromagnetic theory during the acceleration,

  the charged particles lose energy.

➡ This loss of energy slows down the speed of the electron and

  eventually, the electron fall into the nucleus and the atom callapes.

(ii) He does not describe anything about the distribution of the

  electrons and energies of these electrons.

(iii) Structure of atom is similar to solar system, the electrons revolve

  around the nucleus in circular paths.

(iv) The size of the nucleus is very small as compared to the size of the

  Atom.

  He tried to given his best by covering the drawbacks of Rutherford

→ In an atom only special orbits are defined which are discrete in

 nature.

→ These discrete orbits are unique as they passes fixed energies.

→ These energy levels are name K, L, M, N and numbered 1,2,3,4 and so

 on starting from the orbit closet to Nucleus.

(i)Hydrogen →

              <----(Only one electron)

(ii) Silicon →

              ----> No. of electron = 14

→ The maximum number of electron present in a shell is given by the

 formula 2n², where n is the orbit no.

   K = Shell → 2 x (1)² = 2

   L= Shell → 2 x (2)²= 8

   M = Shell → 2 x (3)² = 18

   N = Shell → 2 x (4)² = 32

=> The maximum number of electrons that can be accommodated is

  the outermost orbit is 8

=> So, remains electron will be transfer in next shell.

 In 1932, J. Chadwick is discovered the Neutron

 Neutrons have no change

 Symbol "n"

 Mass of Neutrons = Mass of proton

 Present in nucleus of atom expect hydrogen.

 Sodium → K-Shell = 2 electrons

      L- Shell = 8 electrons

valence shell (M - Shell) = [1 electron] → valence electron

    ↓ ↓

 outermost shell no. of electron in

  of an atom outermost shell

  Valency of sodium is 1. because the valence shell is not stable, for

    stability it has to lose 1 electron

  If the valence shell of an atom is stable the valency of that atom will

 be 0.

→ No. of proton or electron in the atom is called atomic number

→ Sum of no. of proton and neutron is an atom is called mass number

→ denoted by A

* Mass number → No. of proton + No. of neutron

* No. of Neutrons → mass number - Atomic no.

    Mass number←14N7 → Atomic No.

Isotopes

→ They are those element which have same atomic number but

  different mass number

   Eg - H → H₁¹ → H₁² → H₁³

      ↓ ↓ ↓

        protium deuterium tritium

   C → C_6^12 & C_6^14 → Radioactive

      ↓

    Normally use this

    Different mass number hence, no. of neutron present in the nucleus

  are different.

Application

(i) Isotope of uranium is used as a fuel in nuclear reaction.

(ii) An isotope of cobalt is used in the treatment of cancer.

(iii) An isotope of iodine is used in the treatment of goitre.

 They are those elements which have same mass number but different Atomic number.

 Eg: 〖Ar〗_18^40 〖Ca〗_20^40

      〖Na〗_11^24 〖Ma〗_12^24