This document summarizes models of the atom, beginning with discoveries of its subatomic particles. It describes J.J. Thomson's model consisting of a positively charged sphere with embedded electrons. Rutherford's experiments showed a small, dense nucleus at the atom's center. Later models, like Bohr's, proposed electrons orbiting in fixed energy levels to explain atomic stability. The document outlines discoveries of the proton, neutron, and electron and their properties, and summarizes Thomson, Rutherford, and Bohr's atomic models.

1. STRUCTURE OF
ATOM
MADE BY :
PRATIKSHA YADAV
Class : 9th

2. 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

3. Introduction
We 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.

4. 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

5. Discovery of neutron
The Discovery of Neutron particle by chad wick in 1932. The
neutron is a neutral particle found in the nucleus of an atom.
The sub atomic particle not present in a hydrogen atom is
neutron.
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 neutral
EX. Atomic mass of carbon= mass of 6 proton+ mass of 6
neutron
=6×1+6×1
=12u

6. 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*-19
Coulomb of negative charge. The relative charge of an
electron is,-1.

7. Sub particles of an atom
1-Electron
2-Proton 3-Neutron

8. J.J Thomson ‘s model of atom
Thomson 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 .

9. Lead
block
Uranium
Fluorescent
Screen
Gold Foil

10. RESULT

11. 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.

12. Drawbacks of Rutherford ‘s model
of an atom
The 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.

13. Bohr ‘s model of an atom
i)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 .