Class 9  >  Structure Of Atom

Structure Of Atom Notes - Class 9

Document Description: Structure Of Atom for Class 9 2022 is part of Class 9 preparation. The notes and questions for Structure Of Atom have been prepared according to the Class 9 exam syllabus. Information about Structure Of Atom covers topics like and Structure Of Atom Example, for Class 9 2022 Exam. Find important definitions, questions, notes, meanings, examples, exercises and tests below for Structure Of Atom.

Introduction of Structure Of Atom in English is available as part of our Class 9 preparation & Structure Of Atom in Hindi for Class 9 courses. Download more important topics, notes, lectures and mock test series for Class 9 Exam by signing up for free. Class 9: Structure Of Atom Notes - Class 9
1 Crore+ students have signed up on EduRev. Have you?

Science Class 9 Notes – Structure of Atom
1. Sub-Atomic Particles
 Electrons: Electron was discovered in cath¬ode ray experiment.
 The term electron was coined by GJ Stoney
 Protons were discovered in anode ray ex-periment. Anode rays are also called posi¬tive 
rays or canal rays. Protons was discovered by Wilhelm Wien in 1902. It was identified 
by J.J. Thomson.
 Neutron was discovered by James Chadwick in 1932.
2. Atomic Models :
Models are the ideas about how things behave the way they do.
Various Models of atom
(a) Thomson Model or Water Melon Model or Plum pudding Model
According to this model electrons are embedded in the positively charged mass distributed 
uniformly throughout the atomic sphere.
This model was proposed by Joseph James Thomson in 1897. This model is also know as apple 
pie model.
(b) Rutherford’s Model or Planetary Model:
This model is based on experiments conducted by Rutherford. This model was given by Ernest 
Rutherford in 1911.
 According to this model all the positively charged particles are present in a small space 
in the centre of the atom. This small space is called nucleus.
 The electrons revolve around the nucleus just as the planets revolve around the sun. Due 
to this similarity, Rutherford’s model is called the planetary model or Solar model.
 Electrons (negatively charged) revolve around the nucleus in orbits with a high speed to 
overcome the elecro-static force of attraction between positively charged particles 
(protons) present in the nucleus.
Drawbacks of Rutherford’s Model
The two deficiencies of this model are:
 It is possible to have infinite number of orbits. In practice it is not the case.
 The moving electron must continuously lose energy and fall into the nucleus. Actually it 
is not the case.
(c) Bohr’s Atomic Model: This model was given by Neils Bohr in 1913. According to this 
model.
 an atom consists of heavy positively charged nucleus. The whole mass of the atom is 
concentrated in the nucleus.
 The electrons in an atom revolve around the nucleus in definite circular paths called 
orbits or energy level.
 Each energy level is associated with definite amount of energy.
 The change in energy takes place when electron jumps from one energy level to another 
energy level.
3. Arrangement of electrons in an atom : The arrangement of electrons in various shells 
(energy levels) of an atom of the element is known as Electronic configuration.
The Maximum number of electrons that could be put in a particular shell (i.e., energy levels 
was given by Bohr and Bury.
According to Bohr-Bury Scheme
 The maximum number of electrons that can be accommodated in any energy level is 
given by 2n2 where 11 = 1, 2, 3, 4, …. (for K, L, M, N…..)
 The maximum number of electrons in the outermost orbit will be 8 electrons even if it 
has capacity to accommodate more electrons.
 Electrons, are not accommodated in a given shell. Unless earlier shells are filled, that 
is stepwise filling of shells is followed.
4. Valency : The electrons present in the outer most shell of an atom are known as valence 
electrons. These electrons determine the valency of an atom.
Valency is equal to the number of valence electrons.
In case the number of valence electrons is close to its full capacity. Then,
Valency =8— valence electrons
If outermost shell is completely filled then 9. valency is zero.
Valency is the combining capacity of an atom.
5. Atomic number (Z) : Atomic number of an element is equal to the number of protons 
present in the nucleus of an atom.
Atomic number (z) = number of protons = number of electrons.
6. Mass number (A) : It refers to the total num¬ber of neutrons and protons, (i.e., sum of 
pro¬tons and neutrons) called collectively as nucleus, present in an atom.
Mass number (A) = number of protons number of neutron = number of nucleus
7. Isotopes : Atoms of the same element having same atomic number but different mass 
num bers are known as Isotopes eg.
8. Applications of Isotopes : Isotopes are used in, various fields. For example.
 Isotope of uranium is used as a fuel in nuclear reactor
 Isotope of cobalt is used in treatment of cancer
 Isotope of iodine is used in treatment of goitre.
9. Isobars : Atoms of different elements having same mass numbers are known as Isobars, e.g 
K-40 and Ar-40
The document Structure Of Atom Notes - Class 9 is a part of Class 9 category.
All you need of Class 9 at this link: Class 9
Download as PDF

Download free EduRev App

Track your progress, build streaks, highlight & save important lessons and more!

Related Searches

Summary

,

shortcuts and tricks

,

mock tests for examination

,

pdf

,

Free

,

study material

,

Previous Year Questions with Solutions

,

practice quizzes

,

video lectures

,

Sample Paper

,

past year papers

,

Viva Questions

,

Semester Notes

,

MCQs

,

Extra Questions

,

Exam

,

Structure Of Atom Notes - Class 9

,

Objective type Questions

,

Important questions

,

Structure Of Atom Notes - Class 9

,

Structure Of Atom Notes - Class 9

,

ppt

;