STRUCTURE OF ATOM

MADE BY :PRATIKSHA YADAV

Class : 9th

Contents• Introduction

• Discovery of Proton

• Discovery of neutron

•Discovery of electron

•Particle of atom speed

•Thomson ‘s model

•Rutherford ‘s experiment•Rutherford ‘s model

•Drawbacks Rutherford ‘s model

•Bohr ‘s model

IntroductionWe will see many thing chair, table, wood ice in our daily life. Any thing which occupies space and has mass

is called matter. All the matter is made up of tiny particles and

particles are made up of Atom. Atom is the smallest part of the matter.

Discovery of Proton

• The existence of protons in the atoms was shown by E. Goldstein. The proton is a positively charged particle found in the atoms of all the element.

• The two important characteristics of a proton are its mass and charge. These are described below.

• The relative mass of a proton is 1u The absolute mass of a proton is 1.6x 10.24 gram.

• So the absolute charge of a proton is 1.6×10*-19 coulomb of positive charge. The relative charge of a proton is +1

Discovery of neutronThe Discovery of Neutron particle by chad wick in 1932. Theneutron is a neutral particle found in the nucleus of an

atom. The sub atomic particle not present in a hydrogen atom isneutron.The two important characteristics of a neutron are its mass and charge. These are described below.The relative mass of a neutron is 1u. The absolute mass of a neutron is 1.6×10*-24 gram.Neutron has no charge. It is electrically neutralEX. Atomic mass of carbon= mass of 6 proton+ mass of 6 neutron=6×1+6×1=12u

Discovery of electron

The existence of electrons in an atom was shown by J. J. Thomson in 1897. Cathode rays consist of small, negatively charged particles called electrons. The electron is a negatively charged particle found in the atoms of all the element.The two important characteristics of an electron are its mass and charge. These are described below.The relative mass of an electron is 1/1840 u the absolute mass of an electron is , how ever 9 ×10*-28 gram.The absolute charge on an electron is 1.6 ×10*-19Coulomb of negative charge. The relative charge of an electron is,-1.

Sub particles of an atom

1-Electron 2-Proton 3-Neutron

J.J Thomson ‘s model of atomThomson proposed that –i) An atom consists of a positively charged

sphere and the electrons are embedded in it .ii) The negative and positive charges are equal

in magnitude . So , the atom as a whole is electrically neutral .

Lead block

Uranium

Gold Foil

Fluorescent Screen

Rutherford ‘s experiment

RESULT

Rutherford ‘s model of an atom

i)There is a positively charged centre in an atom called nucleus .the whole mass of an atom is concentrated in the nucleus.ii)The electrons revolve around the nucleus in a well – defined orbits.iii)The size of the nucleus is very small as compared to the size of the atom.

Drawbacks of Rutherford ‘s model of an atomThe Rutherford ‘s model does not explain the stability of the atom according to him electron revolves around nucleus continually revolving electron losses their energy and its path decreases and comes near the nucleus ultimately electron should fall into the nucleus but this does not happen because we know that atom is stable.

Bohr ‘s model of an atomi)An atom is made up of electron , proton and neutron .ii)The proton and neutron are located in a small nucleus at the centre of the atom .iii)The electron revolve around the nucleus in fixed circular path called energy level or shells.iv)There is a limit to the number of electrons which each energy level ( or shell ) can hold.v)Each energy shell is associated with a fixed amount of energy .vi)There is no change in the energy of electrons as long as they keep revolving in the same shell and the atom remains stable .